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Displacement Calculator with Steps | Physics & Engine

Displacement Calculator

Find displacement in physics from the motion equations, two points, a path or a velocity function, and work out engine displacement from bore and stroke in cc, litres and cubic inches. Every answer comes with units, steps, two checks and a diagram.

PhysicsKinematicsEngine ccStep by StepAny UnitsFree

⚡ 0. Quick Answer

A displacement calculator finds how far, and in which direction, an object ends up from where it started: final position minus initial position.

A car moving at 5.0 m/s that speeds up at 2.0 m/s² for 4.0 s has a displacement of 36 m. For an engine, displacement is the volume all the pistons sweep: an 86.0 mm bore, 86.0 mm stroke four-cylinder displaces 1998 cc (2.0 L).

Δx = x2 − x1  ·  s = ut + ½at²  ·  V = π/4 × b² × s × n

x and s in metres (m), u in m/s, a in m/s², t in seconds (s); engine bore b and stroke s in cm give V in cm³ (cc).

Rule of thumb: displacement can be smaller than the distance travelled, never larger. Walk 3 km north then 4 km east: the distance is 7 km but the displacement is only 5 km.

Key Takeaways

  • A displacement calculator gives the straight-line change in position with its direction, such as 36 m forward for the worked car problem.
  • Displacement is a vector measured in metres; a walk of 3 km north and 4 km east has a displacement of 5 km on a bearing of about 53°, but a distance of 7 km.
  • With constant acceleration use s = ut + ½at²: u = 5.0 m/s, a = 2.0 m/s², t = 4.0 s gives 36 m, the area under the v-t graph.
  • Engine displacement is π/4 × bore² × stroke × cylinders: 86.0 mm square, four cylinders gives 1998 cc, or 121.9 cubic inches.
  • Water displacement measures volume: a 270 g block that raises water from 50.0 mL to 150.0 mL has a density of 2.70 g/cm³, the density of aluminium.

📚 1. What Is a Displacement Calculator?

Displacement is the change in position of an object: where it ends minus where it started, with a direction. It is a vector, measured in metres (m). If you walk 10 m forward and 10 m back, you have moved 20 m, but your displacement is 0 m because you are back where you began.

1.1 How to calculate displacement in 4 steps

  1. Pick a positive direction (forward, up, east) and write every value with a sign and a unit.
  2. Convert to SI units: km/h ÷ 3.6 = m/s, cm ÷ 100 = m, minutes × 60 = s.
  3. Choose the formula that matches what you know (table 1.2): end minus start, s = vt, or a SUVAT equation.
  4. Substitute, solve and give a direction: s = (5.0)(4.0) + ½(2.0)(4.0)² = 36 m forward.

1.2 Displacement formula: which one to use

What you knowDisplacement formulaWorked example
Start and end positionsΔx = x2 − x1From 3 m to 11 m: Δx = 8 m
Constant velocity and times = vt12 m/s for 5.0 s: s = 60 m
u, a and ts = ut + ½at²5.0 m/s, 2.0 m/s², 4.0 s: s = 36 m
u, v and ts = ½(u + v)t72 km/h to rest in 4.0 s: s = 40 m
u, v and as = (v² − u²) / (2a)20 m/s to 0 at −5.0 m/s²: s = 40 m
Velocity that changes in any ways = ∫ v(t) dtv = 3t² − 12t + 9, 0 to 4 s: s = 4 m
Points in 2D or 3D|d| = √(Δx² + Δy² + Δz²)(2, 3) m to (8, 11) m: |d| = 10 m

1.3 Distance vs displacement

Distance is the whole length of the path. Displacement is the straight line from start to finish, with a direction. They are equal only for a straight trip with no turning back.

Distance of 7 km versus displacement of 5 km for a walk 3 km north then 4 km east3 km N4 km E5 km, bearing 53.1°startfinishNdistance 7 km · displacement 5 km
A route of 3 km north then 4 km east. The blue route is 7 km long (distance). The dark arrow straight from start to finish is 5 km (displacement).
QuantityTypeUnitCan it be negative?Example
DisplacementVector (size and direction)mYes, the sign gives the direction5 km on a bearing of 53°
DistanceScalar (size only)mNo, never7 km walked
VelocityVector, displacement ÷ timem/sYes−3 m/s means moving backwards
SpeedScalar, distance ÷ timem/sNo3 m/s
Engine displacementVolume swept by the pistonscm³ (cc), L, in³No1998 cc = 2.0 L
Displaced volumeVolume of liquid pushed asidemL = cm³No100.0 mL rise

1.4 Engine displacement formula (bore and stroke)

Engine displacement is the total volume swept by all the pistons: V = π/4 × bore² × stroke × cylinders. With bore and stroke in cm the answer is in cc; divide by 1000 for litres and by 16.387064 for cubic inches. An 86.0 mm × 86.0 mm four-cylinder is 1998 cc, sold as a 2.0 L engine.

1.5 Water displacement and density

A sinking solid pushes aside its own volume of water. Read the level before and after, subtract to get the volume, and divide the mass by it: 270 g ÷ 100.0 cm³ = 2.70 g/cm³, the density of aluminium.

1.6 Six calculators in one

A displacement calculator works this out for you, whatever information you have. This one has six ways in, because the word "displacement" is used in three different jobs:

  • Motion equations (SUVAT). Enter any three of displacement s, initial velocity u, final velocity v, acceleration a and time t. The tool finds the other two, and the distance travelled when the object turns round.
  • Between two points. Enter start and end coordinates in 1D, 2D or 3D. You get the components, the size of the displacement and its direction.
  • Path: distance vs displacement. Enter each leg of a trip as a distance and compass bearing. You get the total distance and the net displacement side by side.
  • Velocity function (calculus). Type v(t) such as 3t² − 12t + 9. The tool integrates it to give displacement and distance, and finds the turning points.
  • Engine displacement. Enter bore, stroke and the number of cylinders to get cc, litres and cubic inches. Or solve backwards for the bore or the stroke.
  • Water displacement density. Enter the mass and the water level before and after. You get the volume, the density, the closest material and the buoyant force.

A worked one-liner: a car at u = 5.0 m/s accelerates at a = 2.0 m/s² for t = 4.0 s. Then s = (5.0)(4.0) + ½(2.0)(4.0)² = 20 + 16 = 36 m, and v = 5.0 + 2.0 × 4.0 = 13 m/s.

Who uses it: students in CBSE and ICSE Class 9 to 12, JEE and NEET, IGCSE and GCSE, A level and AP Physics 1 meet displacement in the first chapter of mechanics. First-year university students use the calculus form. Mechanics, car buyers and engine builders use engine displacement in cc or cubic inches. Chemistry and physics labs use water displacement to measure the volume and density of odd-shaped solids, a method that goes back to Archimedes.

🧮 2. Enter Your Values

Solve for (this box becomes the answer):

Fill exactly three boxes and leave the other empty. Negative values mean the opposite direction: for something thrown upwards, take up as positive and use a = −1 g. Scientific notation works: 6.2e-3 or 6.2×10^-3.

Bearings are clockwise from north: 0° north, 90° east, 180° south, 270° west.

Write 3t^2 or 3*t^2 for 3t². Trig functions use radians. Functions: sin, cos, tan, exp, ln, log, sqrt, abs.

Solve for:

Optional: compression ratio, air flow and compressor CFM

Read the bottom of the meniscus at eye level. The object must be fully under the surface.

A header row is skipped automatically. Download Doc gives every answer.

📊 3. Results and Step-by-Step Working

Result
___
Enter your values and press Calculate to see the answer, its units and every step.

🧠 4. Understanding Your Answer, In Detail

___ Press Calculate and this box explains your own answer: what it means, whether it is a sensible size, and how distance and displacement compare.

4.1 What displacement tells you

Displacement answers one question: how far from the start did the object end up, and in which direction? It ignores the route. A runner who laps a 400 m track once has run 400 m, but their displacement is 0 m, because they finish on the start line.

4.2 Is your answer a sensible size?

Compare it with everyday numbers. A person walks at about 1.4 m/s, so 100 m takes a little over a minute. A car at motorway speed (30 m/s) covers about 1 km in 33 s. A dropped stone falls 4.9 m in the first second and 44 m in 3 s. If your answer is 1000 times bigger or smaller than these, check for a km/h or a cm that was not converted.

4.3 The sign is the direction

In one dimension the sign of the displacement tells you the direction. Choose which way is positive before you start, and keep it. A ball thrown up at 20 m/s with up as positive has a = −9.8 m/s². After 3.00 s its displacement is +15.9 m: still above the hand, even though it is already falling.

4.4 Distance can be larger than displacement

Distance counts every metre moved. Displacement only counts start to finish. They are equal only when the object moves in a straight line without turning back. The thrown ball above rises 20.4 m and falls 4.5 m, so the distance is 24.9 m while the displacement is 15.9 m. This calculator gives both.

4.5 How the answer scales

From rest with constant acceleration, s = ½at². Double the time and the displacement becomes four times larger. Double the acceleration and it only doubles. For an engine, a 10% wider bore raises the displacement by 21%, but a 10% longer stroke raises it by just 10%.

4.6 What the v-t graph shows

On a velocity-time graph, the area between the line and the time axis is the displacement. Area above the axis is forward motion; area below counts as negative. The gradient of the line is the acceleration. This is why the calculus mode integrates v(t): integration is adding up area.

4.7 Engine displacement is a volume

For an engine, displacement means the swept volume: the space one piston moves through from top dead centre to bottom dead centre, times the number of cylinders. It is quoted in cc (cm³), litres or cubic inches. The badge on a car is usually rounded: a 1998 cc engine is sold as a 2.0 L.

4.8 Water displacement gives volume

When a solid sinks in water, the water level rises by exactly the solid's volume. Divide its mass by that volume and you have its density. Any density above 22.6 g/cm³ (osmium, the densest element) is a sign of a units mix-up.

✍ 5. How to Write the Answer

▶ Press Calculate above to fill these five cards with your own answer.

1. Exam answer (GRESS)
Given, Required, Equation, Substitute, Answer with unit: ___
Conventions
  • Write every value with its unit in the Given line.
  • Box the final answer and give it to the same significant figures as the data.
  • State which direction is positive when signs matter.
2. Final answer only
___
Conventions
  • A space goes between the number and the unit: 36 m, not 36m.
  • A displacement in 2D needs a size and a direction.
  • Use scientific notation for very large or small values: 9.4 × 1011 m.
3. Lab report results sentence
The displacement was ___ (method ___).
Conventions
  • Name the method (SUVAT, graph area, water displacement).
  • Add ± the uncertainty when you have repeat readings.
  • Write in the past tense, third person.
4. Teacher's answer-key line
Answer key: ___
Conventions
  • Give the marks for equation, substitution and answer.
  • Accept answers within one significant figure of rounding.
  • Accept 9.8 or 9.81 for g unless the paper fixes one.
5. Plain text for a forum or chat
___
Conventions
  • Units are written m/s^2 so they paste anywhere.
  • Arrows (->) separate the inputs from the answers.
  • Keep the sign on vectors.

∑ 6. Formulas Used

①
Displacement: Final Minus Initial Position
Δr = r2 − r1  ·  |Δr| = √(Δx² + Δy² + Δz²)
ΔrDisplacement vector, metres (m)
r1, r2Start and end positions, metres (m)
Δx, Δy, ΔzComponents, metres (m). Each can be negative
Directionθ = atan2(Δy, Δx), degrees (°), from the +x axis
Example(2.0, 3.0) m to (8.0, 11.0) m: |Δr| = √(6.0² + 8.0²) = 10 m
②
Constant-Acceleration (SUVAT) Equations
s = ut + ½at²  ·  s = ½(u + v)t  ·  s = vt − ½at²
sDisplacement, metres (m)
u, vInitial and final velocity, metres per second (m/s)
aAcceleration, metres per second squared (m/s²), constant
tTime, seconds (s). Never negative
Exampleu = 5.0 m/s, a = 2.0 m/s², t = 4.0 s: s = 20 + 16 = 36 m
③
Linking Equations (No Displacement, No Time)
v = u + at  ·  v² = u² + 2as
v = u + atUse when s is not given and not wanted
v² = u² + 2asUse when t is not given and not wanted, units m²/s²
RuleIf u² + 2as is negative, that displacement is never reached
Check13² = 169 and 5.0² + 2(2.0)(36) = 169 ✓
④
Displacement from Velocity (Calculus)
s = ∫ v(t) dt  ·  distance = ∫ |v(t)| dt
v(t)Velocity as a function of time, metres per second (m/s)
dtA tiny time step, seconds (s)
MeaningNet area under the v-t graph. Area below the axis is negative
Examplev = 3t² − 12t + 9 from 0 to 4 s: s = 4 m, distance = 12 m
⑤
Engine Displacement (Swept Volume)
V = π/4 × b² × s × n
VEngine displacement, cubic centimetres (cm³ = cc)
bBore, the cylinder diameter, centimetres (cm)
sStroke, the piston travel, centimetres (cm)
nNumber of cylinders (a whole number)
Rearrangedb = √(4V / (πsn)) · s = 4V / (πb²n)
Example8.60 cm × 8.60 cm, 4 cylinders: 0.785398 × 73.96 × 8.60 × 4 = 1998 cc
⑥
Density by Water Displacement (Archimedes)
V = V2 − V1  ·  ρ = m / V  ·  Fb = ρliquid V g
V1, V2Water level before and after, millilitres (1 mL = 1 cm³)
mMass, grams (g) or kilograms (kg)
ρDensity, g/cm³ (1 g/cm³ = 1000 kg/m³)
FbBuoyant force, newtons (N)
Example270 g, 50.0 to 150.0 mL: ρ = 270 ÷ 100.0 = 2.70 g/cm³
⑦
Constants and Exact Conversions Used
g0 = 9.80665 m/s²  ·  1 in = 2.54 cm  ·  1 in³ = 16.387064 cm³
g0Standard gravity, 9.80665 m/s² (exact, defined). Choose 9.81, 9.8 or 10 to match your exam board
km/hDivide by 3.6 to get m/s (exact)
1 L1000 cm³ (cc), exact
1 CFM28.316846592 L/min, exact

🔀 7. Displacement Calculator Flowchart, Step by Step

This flowchart shows how a displacement calculator works, step by step, on the worked problem used across this page: a car moving at 5.0 m/s accelerates at 2.0 m/s² for 4.0 s. Find its displacement.

Start or result Data step Calculation step Yes or no check
StartCar speeding up on a straight roadu = 5.0 m/s, a = 2.0 m/s², t = 4.0 s. Forward is positive.
1
List s, u, v, a, t and mark the unknowns = ?, u = 5.0 m/s, v = not needed, a = 2.0 m/s², t = 4.0 s
2
Convert every value to SI unitsAll already in m/s, m/s² and s. (72 km/h would become 72 ÷ 3.6 = 20 m/s.)
CheckIs the acceleration constant?
YesA steady 2.0 m/s², so the SUVAT equations apply.
No, stopUse the area under the v-t graph or integrate v(t) (calculus mode).
3
Pick the equation without vs = ut + ½at²Contains s, u, a and t: the three knowns and the unknown.
4
Substitute with unitss = (5.0 m/s)(4.0 s) + ½(2.0 m/s²)(4.0 s)²= 20 m + 16 m
5
Solves = 20 + 16s = 36 m forward
CheckDoes a second equation agree?
Yesv = 5.0 + 2.0 × 4.0 = 13 m/s; v² = 169 = 5.0² + 2(2.0)(36). Carry on.
No, stopA sign or a conversion is wrong. Go back to step 2.
CheckDid the velocity change sign?
Nou and v are both positive, so distance = |s| = 36 m.
YesSplit at v = 0 to find the distance; the displacement stays the same.
6
Round to the data's significant figuresThe data have 2 s.f., so s = 36 m (2 s.f.)
Results = 36 m forward, v = 13 m/sUnits check ✓ VerifiedSame answer as the Excel sheet (Section 9), the R script (Section 10) and the Python script (Section 11).

The same steps work for engine displacement: list bore, stroke and cylinders; convert to cm; check the bore is a diameter; apply V = π/4 × b² × s × n; and check by substituting back. For 86.0 mm × 86.0 mm × 4 that gives 1998 cc. Sections 9, 10, 11 and 14 do both by hand and in software.

📝 8. How to Use This Calculator

  1. Choose the type of problem. Pick a tab: Motion (SUVAT), Two Points, Distance vs Displacement, v(t) Calculus, Engine cc, Water Displacement or Batch.
  2. Choose what to solve for. In the SUVAT and Engine tabs, tap the chip for the unknown. Its box turns into a dashed question mark.
  3. Type your values. Fill the boxes you know. For SUVAT fill exactly three of s, u, v, a and t.
  4. Pick a unit for each value. Every box has its own unit list, such as km/h, mph, ft, in or g. The calculator converts to SI units for you.
  5. Set signs for direction. Choose which way is positive and give values in the opposite direction a minus sign.
  6. Choose g and significant figures. Set g to match your exam board (9.80665, 9.81, 9.8 or 10 m/s²). Leave significant figures on Match the data unless your teacher says otherwise.
  7. Or load a sample problem. Fourteen samples cover cars, constant velocity, free fall, a thrown ball, a walk, calculus, engines and a density trap. Nothing is calculated until you press Calculate.
  8. Press Calculate. Or press Enter in any box. The answer appears with its unit, other units, two check badges and a model note.
  9. Read the working. The GRESS table and the numbered steps show every conversion, equation and substitution, ready to copy into an exam answer.
  10. Check the diagram and charts, then download. The live diagram and four charts are drawn from your numbers. Download Doc saves the full working as text; Download PDF prints it.

📈 9. How to Calculate Displacement in Excel

Excel has no DISPLACEMENT function, but each formula on this page is one line of arithmetic. Put one problem on each row, write the unit in every column header, and copy the formula down. The worked numbers are the same as Sections 7, 10 and 11: u = 5.0 m/s, a = 2.0 m/s², t = 4.0 s, and an 86.0 mm × 86.0 mm four-cylinder engine.

The whole thing in one cell: with u in B2, a in C2 and t in D2, type =B2*D2+0.5*C2*D2^2. That is s = ut + ½at², and it returns 36 (metres).

9.1 The functions you need

You wantExcel formulaNote
Displacement from u, a, t=B2*D2+0.5*C2*D2^2s = ut + ½at²
Final velocity=B2+C2*D2v = u + at
Displacement from u, v, t=0.5*(B2+C2)*D2s = ½(u + v)t
Displacement from u, v, a=(C2^2-B2^2)/(2*D2)s = (v² − u²)/(2a); a must not be 0
Size of a 2D displacement=SQRT((C2-A2)^2+(D2-B2)^2)Pythagoras on Δx and Δy
Direction from +x=DEGREES(ATAN2(C2-A2,D2-B2))Excel's ATAN2 takes x first, then y
Engine displacement in cc=PI()/4*B2^2*C2*D2/1000Bore and stroke in mm; ÷1000 turns mm³ into cc
cc to cubic inches=E2/16.3870641 in³ = 16.387064 cc exactly
km/h to m/s=B2/3.6Exact
Density from water displacement=B2/(D2-C2)Mass in g, levels in mL: answer in g/cm³

9.2 Step by step

1 Lay out one problem per row, units in the headers

Type u (m/s), a (m/s²) and t (s) in B, C and D. Put the displacement formula in E2.

=B2*D2+0.5*C2*D2^2
Xdisplacement.xlsx - ExcelE2fx=B2*D2+0.5*C2*D2^2ABCDE1Problemu (m/s)a (m/s²)t (s)s (m)2Car5.02.04.0363Bike3.00.56.0274Drop09.813.0044.145

E2 returns 36: the car's displacement in metres.

2 Add the final velocity and a check column

F2 finds v. G2 tests v² = u² + 2as, which must give 0. A non-zero check means a typing error.

=B2+C2*D2=F2^2-(B2^2+2*C2*E2)
Xdisplacement.xlsx - ExcelG2fx=F2^2-(B2^2+2*C2*E2)ABCDEFG1Problemu (m/s)a (m/s²)t (s)s (m)v (m/s)check2Car5.02.04.0361303Bike3.00.56.02760

v = 13 m/s and the check is 0, so the answer is consistent.

3 Displacement between two points

Put x₁, y₁, x₂, y₂ in A to D. E2 gives the size and F2 the direction.

=SQRT((C2-A2)^2+(D2-B2)^2)=DEGREES(ATAN2(C2-A2,D2-B2))
Xpoints.xlsx - ExcelF2fx=DEGREES(ATAN2(C2-A2,D2-B2))ABCDEF1x1 (m)y1 (m)x2 (m)y2 (m)|d| (m)θ (°)22.03.08.011.01053.1336-2-31015126.87

From (2, 3) m to (8, 11) m: 10 m at 53.13° from the x axis.

4 Engine displacement in cc, litres and cubic inches

Bore and stroke in mm, cylinders as a whole number. Divide by 1000 for cc, by another 1000 for litres.

=PI()/4*B2^2*C2*D2/1000=E2/1000=E2/16.387064
Xengine.xlsx - ExcelE2fx=PI()/4*B2^2*C2*D2/1000ABCDEFG1Enginebore (mm)stroke (mm)cylccLin³22.0 L86.086.041998.232.00121.94312552.457.91124.860.127.62

86.0 × 86.0 mm, 4 cylinders: 1998.23 cc, 2.00 L, 121.94 in³.

9.3 The awkward cases

  • Trig takes radians. =SIN(30) gives −0.988, not 0.5. Wrap degrees: =SIN(RADIANS(30)). Use =DEGREES(...) to turn an ATAN2 answer back into degrees.
  • ATAN2 argument order. Excel is ATAN2(x, y). Python and R are atan2(y, x). Swapping them gives the complementary angle.
  • Negative square. =-3^2 returns 9 in Excel, because the minus is applied first. Write =-(3^2) or keep signs inside brackets.
  • Large and small numbers. Format the cell as Scientific (0.00E+00) to see 9.40E+11 m for an orbit. Excel keeps about 15 significant digits.
  • Solving for time. When t is the unknown, use Data → What-If Analysis → Goal Seek: set E2 to your displacement by changing D2.

9.4 Why Excel might disagree with R, Python or this page

SituationWhat happensFix
Different gFor a 3.00 s drop, 9.8 gives 44.10 m, 9.81 gives 44.15 m and 10 gives 45.00 mMatch the g selector on this page to your sheet
RoundingExcel ROUND is half away from zero; R and Python round() go half to evenOnly round the final answer
Degrees vs radiansAngles come out wildly wrongUse RADIANS() and DEGREES()
Typed constants3.14 for π changes the fourth significant figure of an engine sizeUse PI(), pi or math.pi
Unit left in km/hAnswer 3.6 times too big for a speed termDivide by 3.6 in its own column

9.5 Charting it

  1. Make a column of times (0, 0.5, 1.0 … 4.0 s) and a column of s with the SUVAT formula.
  2. Insert → Scatter → Scatter with Smooth Lines. Never use the Line chart type: it spaces x values evenly whatever they are.
  3. Add axis titles with units: "time t (s)" and "displacement s (m)".
  4. For lab data, plot s against t² and add a linear trendline with its equation. The gradient is ½a.

9.6 Errors you will hit

Excel showsWhyFix
#NUM!Square root of a negative, for example v² = u² + 2as below zeroThe displacement is never reached. Check the signs of a and s
#DIV/0!Dividing by a = 0 in (v² − u²)/(2a), or by an empty cellUse a different SUVAT equation, or fill the cell
#VALUE!A unit typed into a number cell, such as "5 m/s"Keep units in the header only
#NAME?A misspelt function such as =SQR()Use SQRT, PI(), ATAN2

📈 10. How to Calculate Displacement in R

This base-R script solves the same problems as the page: the car (36 m), two points (10 m at 53.13°) and the engine (1998.2 cc). It checks the answer with a second equation, works out the distance travelled, and saves one 300 dpi v-t graph with the displacement shaded.

Copy the whole block. It runs in RStudio, Posit Cloud or with Rscript displacement.R. Change only the values in part 1, 3 or 4. No packages are needed.

10.1 The complete script

R, base only, saves displacement_vt.png

# ============================================================
# Displacement calculator in R: motion (SUVAT), two points,
# a walked path, and engine displacement, with one 300 dpi plot
# StatsUnlock - https://statsunlock.com/displacement-calculator/
# Base R only. No packages to install.
# ============================================================

# ---- 1. Your values (SI units: m, s, m/s, m/s^2) -----------
u <- 5.0     # initial velocity, m/s
a <- 2.0     # acceleration, m/s^2
t <- 4.0     # time, s

g <- 9.80665 # standard gravity, m/s^2 (use 9.81 or 9.8 to match your exam board)

# ---- 2. Motion: s = ut + 1/2 a t^2 and v = u + at ----------
s <- u * t + 0.5 * a * t^2
v <- u + a * t
cat(sprintf("Displacement s = %.4g m\n", s))
cat(sprintf("Final velocity v = %.4g m/s\n", v))

# check with a second equation: v^2 = u^2 + 2as
check <- abs(v^2 - (u^2 + 2 * a * s)) < 1e-9
cat("Check v^2 = u^2 + 2as:", ifelse(check, "OK", "FAILED"), "\n")

# distance travelled (differs from |s| if the object turns round)
t_turn <- if (a != 0) -u / a else NA
if (!is.na(t_turn) && t_turn > 0 && t_turn < t) {
  s_turn <- u * t_turn + 0.5 * a * t_turn^2
  distance <- abs(s_turn) + abs(s - s_turn)
} else {
  distance <- abs(s)
}
cat(sprintf("Distance travelled = %.4g m\n", distance))

# ---- 3. Displacement between two points --------------------
p1 <- c(2.0, 3.0)    # start (x, y) in m
p2 <- c(8.0, 11.0)   # end (x, y) in m
d <- p2 - p1
mag <- sqrt(sum(d^2))
theta <- atan2(d[2], d[1]) * 180 / pi   # degrees from +x
cat(sprintf("Two points: |d| = %.4g m at %.4g degrees\n", mag, theta))

# ---- 4. Engine displacement --------------------------------
bore_mm <- 86.0; stroke_mm <- 86.0; cylinders <- 4
cc <- pi / 4 * (bore_mm / 10)^2 * (stroke_mm / 10) * cylinders
cat(sprintf("Engine: %.1f cc = %.2f L = %.2f cubic inches\n", cc, cc / 1000, cc / 16.387064))

# ---- 5. One publication-ready figure: v-t graph ------------
tt <- seq(0, t, length.out = 100)
vv <- u + a * tt
png("displacement_vt.png", width = 6, height = 4, units = "in", res = 300)
par(mar = c(4.5, 4.5, 2.5, 1))
plot(tt, vv, type = "l", lwd = 3, col = "#2563eb", ylim = c(0, max(vv) * 1.1),
     xlab = "time t (s)", ylab = "velocity v (m/s)",
     main = sprintf("Area under the v-t line = displacement = %.4g m", s))
polygon(c(0, tt, t), c(0, vv, 0), col = adjustcolor("#2563eb", alpha.f = 0.22), border = NA)
invisible(dev.off())
cat("Saved displacement_vt.png\n")

Output when run: Displacement s = 36 m; Final velocity v = 13 m/s; Check OK; Distance travelled = 36 m; Two points: |d| = 10 m at 53.13 degrees; Engine: 1998.2 cc = 2.00 L = 121.94 cubic inches.

10.2 What each part does

LineWhat it does
s <- u * t + 0.5 * a * t^2The SUVAT equation. ^ is the power operator in R
abs(v^2 - (u^2 + 2*a*s))Substitutes the answer into a second equation. Zero means verified
t_turn <- -u / aThe moment v = 0. If it falls inside the time, distance and displacement differ
atan2(d[2], d[1])Direction in radians, y first then x. Multiply by 180/pi for degrees
cc / 16.387064Exact cc to cubic inch conversion
png(..., res = 300)Opens a 300 dpi image file; dev.off() closes and saves it

R traps: trig functions use radians; round() goes half to even, so round(2.5) is 2; -2^2 is −4 because ^ binds tighter than the minus; log() is the natural log.

10.3 What the figure shows

The blue line is v = 5.0 + 2.0t. The shaded area under it is a trapezium of width 4.0 s and heights 5.0 and 13 m/s, so its area is ½(5.0 + 13)(4.0) = 36 m: the displacement. The title prints the same number the script calculates.

10.4 Common problems and fixes

  • "object not found": run the script from the top, so u, a and t exist before they are used.
  • No PNG appears: look in getwd(), the working directory, or give a full path to png().
  • Wrong answer in km/h: convert first with u <- 72 / 3.6.

10.5 Useful one-liners

TaskR
Time to reach s from restsqrt(2 * s / a)
3D displacement sizesqrt(sum((p2 - p1)^2))
Displacement from v(t)integrate(function(t) 3*t^2 - 12*t + 9, 0, 4)$value
Net displacement of a pathsqrt(sum(dx)^2 + sum(dy)^2)
Engine cc from bore and stroke in mmpi/4 * (b/10)^2 * (s/10) * n

🐍 11. How to Calculate Displacement in Python

The Python version does everything the R script does and adds the calculus case: it integrates v(t) = 3t² − 12t + 9 with SciPy to get a displacement of 4 m and a distance of 12 m. It saves the same 300 dpi v-t graph.

numpyArrays and vector length
scipyg = 9.80665 and quad() integration
matplotlibThe 300 dpi figure

Install once with pip install numpy scipy matplotlib.

11.1 The complete script

Python 3 with NumPy, SciPy and Matplotlib, saves displacement_vt.png

# ============================================================
# Displacement calculator in Python: motion (SUVAT), two points,
# v(t) integration and engine displacement, with one 300 dpi plot
# StatsUnlock - https://statsunlock.com/displacement-calculator/
# pip install numpy scipy matplotlib
# ============================================================
import math
import numpy as np
from scipy.constants import g          # 9.80665 m/s^2 (standard gravity)
from scipy.integrate import quad
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt

# ---- 1. Your values (SI units: m, s, m/s, m/s^2) -----------
u = 5.0   # initial velocity, m/s
a = 2.0   # acceleration, m/s^2
t = 4.0   # time, s

# ---- 2. Motion: s = ut + 1/2 a t^2 and v = u + at ----------
s = u * t + 0.5 * a * t**2
v = u + a * t
print(f"Displacement s = {s:.4g} m")
print(f"Final velocity v = {v:.4g} m/s")
print("Check v^2 = u^2 + 2as:", "OK" if math.isclose(v**2, u**2 + 2*a*s) else "FAILED")

# ---- 3. Displacement between two points --------------------
p1 = np.array([2.0, 3.0])    # start (x, y) in m
p2 = np.array([8.0, 11.0])   # end (x, y) in m
d = p2 - p1
mag = np.linalg.norm(d)
theta = math.degrees(math.atan2(d[1], d[0]))   # degrees from +x
print(f"Two points: |d| = {mag:.4g} m at {theta:.4g} degrees")

# ---- 4. Displacement and distance from v(t) ----------------
def vel(tt):
    return 3*tt**2 - 12*tt + 9          # m/s
disp, _ = quad(vel, 0, 4)
dist, _ = quad(lambda tt: abs(vel(tt)), 0, 4, points=[1, 3])
print(f"v(t) = 3t^2 - 12t + 9 from 0 to 4 s: displacement = {disp:.4g} m, distance = {dist:.4g} m")

# ---- 5. Engine displacement --------------------------------
bore_mm, stroke_mm, cylinders = 86.0, 86.0, 4
cc = math.pi / 4 * (bore_mm / 10)**2 * (stroke_mm / 10) * cylinders
print(f"Engine: {cc:.1f} cc = {cc/1000:.2f} L = {cc/16.387064:.2f} cubic inches")
print(f"(g used elsewhere: {g} m/s^2)")

# ---- 6. One publication-ready figure: v-t graph ------------
tt = np.linspace(0, t, 100)
vv = u + a * tt
fig, ax = plt.subplots(figsize=(6, 4))
ax.plot(tt, vv, color="#2563eb", lw=3)
ax.fill_between(tt, 0, vv, color="#2563eb", alpha=0.22)
ax.set_xlabel("time t (s)")
ax.set_ylabel("velocity v (m/s)")
ax.set_title(f"Area under the v-t line = displacement = {s:.4g} m")
ax.set_ylim(0, vv.max() * 1.1)
fig.savefig("displacement_vt.png", dpi=300, bbox_inches="tight")
print("Saved displacement_vt.png")

Output when run: Displacement s = 36 m; v = 13 m/s; Check OK; Two points: |d| = 10 m at 53.13 degrees; v(t) displacement = 4 m, distance = 12 m; Engine: 1998.2 cc = 2.00 L = 121.94 cubic inches.

11.2 What each part does

LineWhat it does
from scipy.constants import gStandard gravity, 9.80665 m/s². Your syllabus may use 9.8 or 9.81
s = u*t + 0.5*a*t**2SUVAT. Python uses ** for powers; ^ is bitwise XOR
np.linalg.norm(d)Length of the displacement vector in any number of dimensions
math.atan2(d[1], d[0])Direction in radians, y first; math.degrees converts
quad(vel, 0, 4)Integrates v(t) for the displacement
quad(lambda tt: abs(vel(tt)), ..., points=[1, 3])Integrates |v| for the distance, telling SciPy where v changes sign

Python traps: math.sin takes radians; round(2.5) is 2 (half to even); floats hold about 15 to 16 digits; format significant figures with f"{x:.3g}".

11.3 What the figure shows

The same trapezium as the R figure: area 36 m under a line rising from 5.0 to 13 m/s. Change u, a or t and the shaded area and the title change together.

11.4 Common problems and fixes

  • ModuleNotFoundError: run pip install numpy scipy matplotlib in the same environment as Python.
  • Distance equals displacement when it should not: pass the turning points to quad with points=.
  • No window opens: the script saves a file instead of showing a window. Look for displacement_vt.png.

11.5 Useful one-liners

TaskPython
Free-fall displacement after t0.5 * g * t**2
Net displacement of a walknp.hypot(sum(dx), sum(dy))
Bearing from north(90 - math.degrees(math.atan2(dy, dx))) % 360
Bore from cc, stroke and cylindersmath.sqrt(4*cc / (math.pi*s_cm*n))
Density by water displacementm_g / (v2_ml - v1_ml)

Run it in a terminal (python displacement.py), in Jupyter, or paste it into Google Colab.

📋 12. Reference Tables

12.1 Constants and exact conversions

QuantityValueStatus
Standard gravity g09.80665 m/s²Exact (defined)
1 inch2.54 cmExact
1 cubic inch16.387064 cm³ (cc)Exact
1 litre1000 cm³ = 1000 mLExact
1 km/h1/3.6 m/s = 0.27778 m/sExact ratio
1 mile1609.344 mExact
1 astronomical unit149 597 870 700 mExact (IAU 2012)

Source: NIST CODATA 2022 and the SI Brochure for g0; IAU Resolution B2 (2012) for the astronomical unit.

12.2 Length and speed conversions

FromTo SIFromTo SI
1 cm0.01 m1 km/h0.27778 m/s
1 km1000 m1 mph0.44704 m/s
1 ft0.3048 m1 ft/s0.3048 m/s
1 yd0.9144 m1 knot0.51444 m/s
1 mi1609.344 m1 g9.80665 m/s²

12.3 Typical displacements and speeds

SituationTypical value
Walking1.4 m/s, about 84 m in a minute
Sprinter, 100 m race100 m in about 10 s, top speed about 12 m/s
Stone dropped for 1.00 s / 3.00 s4.90 m / 44.1 m (g = 9.80665 m/s², no air resistance)
Car braking hardAbout 7 to 8 m/s²: 40 m to stop from 72 km/h at 5 m/s²
Earth in one yearDistance 9.40 × 1011 m, displacement about 0 m

12.4 Engine displacement units and typical sizes

EngineccLitresCubic inches
Small scooter, 1 cylinder1250.1257.6
City car, 3 cylinders9991.061.0
Family car, 4 cylinders14981.591.4
86.0 × 86.0 mm, 4 cylinders19982.0121.9
V8, 4.000 in × 3.480 in57335.7349.8 (sold as "350")

Sizes are swept volume from the formula V = π/4 × b² × s × n. Makers often round the badge figure.

12.5 Densities for the water displacement method

Materialg/cm³Materialg/cm³
Cork0.24Aluminium2.70
Ice0.917Iron7.87
Water (about 4 °C)1.000Copper8.96
PVC plastic1.38Lead11.34
Glassabout 2.5Gold19.32
Graniteabout 2.75Osmium (densest element)22.59

Room-temperature values, rounded. Glass, granite and wood vary with composition.

12.6 SI prefixes you will meet

PrefixSymbolFactorExample
millim10−31 mm = 0.001 m
centic10−21 cm = 0.01 m
kilok1031 km = 1000 m
megaM1061 Mm = 106 m

📈 13. Example Results

1
TEXTBOOK CASE

A cyclist speeding up

The standard s = ut + ½at² question.

A cyclist moving at 3.0 m/s accelerates at 0.50 m/s² for 6.0 s. Find the displacement and the final velocity.

u = 3.0 m/sa = 0.50 m/s²t = 6.0 ss = 27 mv = 6.0 m/s
QuantityValueNote
s = ut + ½at²18 + 9.0 = 27 mDisplacement
v = u + at3.0 + 3.0 = 6.0 m/sFinal velocity
v² = u² + 2as36 = 9 + 27 ✓Check
Velocity-time graph of a cyclist from 3 to 6 metres per second over 6 seconds; area 27 metres06time t (s)36v (m/s)area = 27 m
The shaded trapezium has area ½(3 + 6)(6) = 27 m.

What it means: The cyclist ends 27 m further along the road. The motion is in one direction, so the distance is also 27 m.

How to write it: s = 27 m in the direction of motion (2 s.f.).

2
EXAM: SOLVE FOR TIME

How long to cover 50 m from rest?

Solving for a variable other than s.

A car starts from rest and accelerates at 4.0 m/s². How long does it take to cover 50 m, and how fast is it then?

u = 0a = 4.0 m/s²s = 50 mt = 5.0 sv = 20 m/s
QuantityValueNote
t = √(2s/a)√(2 × 50 / 4.0) = 5.0 sFrom s = ½at²
v = u + at0 + 4.0 × 5.0 = 20 m/sFinal velocity
Checkv² = 400 = 2 × 4.0 × 50 ✓v² = u² + 2as
Displacement-time curve s = 2t squared reaching 50 metres at 5 seconds05time t (s)050s (m)s = 2.0t² reaches 50 m at t = 5.0 s
A curve, not a straight line: from rest, displacement grows with t².

What it means: After 5.0 s the car has covered 50 m and is moving at 20 m/s (72 km/h). In the calculator, choose Time t as the unknown.

How to write it: t = 5.0 s (2 s.f.); v = 20 m/s.

3
NON-SI INPUTS

A train slowing from 90 to 54 km/h

Convert km/h before you calculate.

A train slows steadily from 90 km/h to 54 km/h over 400 m. Find its acceleration and the time taken.

u = 90 km/h = 25 m/sv = 54 km/h = 15 m/ss = 400 ma = −0.50 m/s²t = 20 s
QuantityValueNote
Convert90 ÷ 3.6 = 25 m/s; 54 ÷ 3.6 = 15 m/sSI units
a = (v² − u²)/(2s)(225 − 625)/800 = −0.50 m/s²Negative: slowing down
t = (v − u)/a(15 − 25)/(−0.50) = 20 sTime
Velocity-time graph of a train slowing from 25 to 15 metres per second in 20 seconds; area 400 metres020time t (s)2515v (m/s)area = 400 m
Check: the area under the line, ½(25 + 15)(20), is 400 m, the displacement given.

What it means: Left in km/h, the same numbers give an acceleration 13 times too big (3.6²). The minus sign shows the train is decelerating.

How to write it: a = −0.50 m/s² (deceleration of 0.50 m/s²), t = 20 s.

4
EVERYDAY ENGINE

Is a "125" scooter really 125 cc?

Engine displacement from bore and stroke.

A single-cylinder scooter engine has a 52.4 mm bore and a 57.9 mm stroke. Find its displacement.

bore = 52.4 mmstroke = 57.9 mmn = 1V = 124.9 cc7.62 in³
QuantityValueNote
Piston areaπ/4 × 5.24² = 21.57 cm²Bore is a diameter
Swept volume21.57 × 5.79 = 124.9 ccOne cylinder
Cubic inches124.9 ÷ 16.387 = 7.62 in³Exact factor
Cylinder cross-section of a 125 cc scooter engine, bore 52.4 mm and stroke 57.9 mmstroke 57.9 mmbore 52.4 mm124.9 cc1 × 124.9 cc = 124.9 cc
The cylinder is drawn to scale: the stroke is slightly longer than the bore, so this engine is undersquare.

What it means: The badge rounds 124.9 cc to 125. A 10% bigger bore would give 151 cc, which is how many 150 cc versions are made.

How to write it: V = π/4 × 5.24² × 5.79 × 1 = 124.9 cc (0.125 L).

5
EXTREME MAGNITUDE

The Earth after one year

A huge distance with zero displacement.

The Earth goes once round the Sun in a year, on a nearly circular orbit of radius 1 AU = 1.496 × 1011 m.

r = 1.496 × 1011 mt = 1 yeardistance = 9.40 × 1011 mdisplacement = 0 m
QuantityValueNote
Distance2πr = 9.40 × 1011 mCircumference of the orbit
Displacement0 mSame start and end point
Average speed9.40 × 1011 ÷ 3.156 × 107 s = 29.8 km/sDistance ÷ time
Average velocity0 m/sDisplacement ÷ time
The Earth returns to its starting point after one orbit of the SunSunstart = enddistance 9.40 × 10¹¹ m · displacement 0 mOne orbit of the Earth in one year
Start and end coincide, so the displacement is zero however far the Earth travels.

What it means: Average speed is about 30 km/s, but average velocity over the year is zero. This is the clearest case of distance and displacement being completely different.

How to write it: distance = 9.40 × 1011 m; displacement = 0 m.

6
NOT PHYSICAL

Grams typed as kilograms

A density far beyond any real material.

A 270 g block raises water from 50.0 mL to 150.0 mL, but the mass is entered as 270 kg.

m = 270 kg (wrong)V = 100.0 mLρ = 2700 g/cm³osmium = 22.59 g/cm³
QuantityValueNote
Volume150.0 − 50.0 = 100.0 cm³Water displacement
Density (wrong unit)270 000 g ÷ 100.0 cm³ = 2700 g/cm³Impossible
Density (correct)270 g ÷ 100.0 cm³ = 2.70 g/cm³Aluminium
Measuring cylinders before and after with an impossible density marked50 mL150 mLV = 100 mL · 2700 g/cm³: not physical
The water rise is correct; the fuchsia block marks a density that cannot exist.

What it means: Nothing is denser than about 22.6 g/cm³. A result 1000 times too big points straight at a g and kg mix-up, and the calculator flags it as Not physical.

How to write it: After correcting the unit: ρ = 270 g / 100.0 cm³ = 2.70 g/cm³.

7
MODEL LIMIT

A skydiver: where SUVAT breaks down

Air resistance means a is not constant.

A skydiver falls from rest for 10.0 s. SUVAT with g = 9.81 m/s² is compared with a quadratic-drag model with a terminal speed of 53 m/s.

t = 10.0 sSUVAT: 490.5 mwith drag: 338.5 mv: 98.1 vs 50.4 m/s
QuantityValueNote
No air resistance½ × 9.81 × 10.0² = 490.5 mSUVAT
Quadratic drag(vt²/g) ln cosh(gt/vt) = 338.5 mvt = 53 m/s
Speed after 10 s98.1 m/s vs 50.4 m/sDrag limits the speed
Fall distance of a skydiver with and without air resistance over 10 seconds010time t (s)0500fall (m)no drag: 490.5 mwith drag: 338.5 m
Dashed blue: constant acceleration. Orange: with drag. They agree for the first 2 s, then split.

What it means: SUVAT overestimates the fall by about 45% here, because the acceleration falls towards zero as drag grows. Use SUVAT only while air resistance is small.

How to write it: Ignoring air resistance, s = 490.5 m; with drag the real value is about 340 m.

8
TRAP: WRONG QUADRANT

tan⁻¹ gives the wrong direction

Why the calculator uses atan2.

A drone flies from (6, −2) m to (−3, 10) m. Find the size and direction of its displacement.

Δx = −9 mΔy = 12 m|d| = 15 matan2: 126.87°tan⁻¹: −53.13° (wrong)
QuantityValueNote
ComponentsΔx = −3 − 6 = −9 m; Δy = 10 − (−2) = 12 mEnd minus start
Size√(81 + 144) = 15 mPythagoras
Directionatan2(12, −9) = 126.87°Second quadrant
Displacement vector from (6, -2) to (-3, 10) pointing up and to the left|d| = 15 m at 126.87° from +x
The arrow points up and to the left, in the second quadrant, at 126.87° from +x.

What it means: tan⁻¹(12 / −9) gives −53.13°, which points down and to the right: exactly the opposite way. Add 180° when Δx is negative, or use atan2.

How to write it: |d| = 15 m at 126.87° from the +x axis (bearing 323.13°).

✏️ 14. How to Calculate Displacement by Hand, Step by Step

This is the written method examiners expect, worked on the same example as Sections 7, 9, 10 and 11: a car moving at 5.0 m/s accelerates at 2.0 m/s² for 4.0 s. Find its displacement and final velocity.

14.1 The written method (GRESS)

  1. Given. u = 5.0 m/s, a = 2.0 m/s², t = 4.0 s. Forward is positive.
  2. Required. s (displacement, m) and v (final velocity, m/s).
  3. Equation. s = ut + ½at² (it has no v), then v = u + at.
  4. Substitute, with units. s = (5.0 m/s)(4.0 s) + ½(2.0 m/s²)(4.0 s)². v = 5.0 m/s + (2.0 m/s²)(4.0 s).
  5. Solve. s = 20 + 16 = 36 m. v = 5.0 + 8.0 = 13 m/s.
  6. Check the units and the size. (m/s)(s) = m and (m/s²)(s²) = m. Check: v² = 169 and u² + 2as = 25 + 144 = 169. Both agree.
  7. Write the answer. s = 36 m forward, v = 13 m/s (2 significant figures, matching the data).

Engine version by hand: bore 86.0 mm = 8.60 cm, stroke 8.60 cm. Area = π/4 × 8.60² = 58.09 cm². One cylinder = 58.09 × 8.60 = 499.6 cm³. Four cylinders = 1998 cc = 2.0 L.

14.2 On a scientific calculator

TaskKeysDisplay
s = ut + ½at²5 × 4 + 0.5 × 2 × 4 x² =36
v = u + at5 + 2 × 4 =13
2D displacement size√ 6 x² + 8 x² ) =10
Direction (DEG mode)SHIFT tan 8 ÷ 6 ) =53.13010235
Engine ccπ ÷ 4 × 8.6 x² × 8.6 × 4 =1998.228857

Check the screen shows D (degrees) before any angle work. tan−1(Δy/Δx) only gives the right angle when Δx is positive; add 180° when Δx is negative. Type each line in one go instead of rounding in the middle.

14.3 Measure it yourself: two school lab practicals

A. Displacement of a trolley on a ramp

  1. Set a ramp at 5 to 10°. Mark 0.25 m, 0.50 m and 1.00 m from the release point.
  2. Release the trolley from rest (u = 0). Time it to each mark with light gates, or film it at 60 frames per second and count frames.
  3. Repeat each distance three times and average the times.
  4. Plot s against t². For u = 0, s = ½at², so the gradient is ½a.
  5. Errors: reaction time with a stopwatch (about 0.2 s), friction, a push at release. Light gates or video remove the reaction-time error.
s (m)t1 (s)t2 (s)t3 (s)mean t (s)t² (s²)
0.250.710.700.720.710.50
0.501.001.010.991.001.00
1.001.421.411.431.422.02

The gradient of s against t² is about 0.50 m/s², so a ≈ 1.0 m/s². In the Batch tab enter each row as 0, 1.0, t to compare predicted and measured s.

B. Density of a solid by water displacement

  1. Find the mass of the solid on a balance (for example 270 g).
  2. Half fill a 250 mL measuring cylinder and read the bottom of the meniscus at eye level (50.0 mL).
  3. Tilt the cylinder and slide the solid in on a thread so no water splashes out.
  4. Read the new level (150.0 mL). The rise, 100.0 mL, is the volume of the solid in cm³.
  5. Density = mass ÷ volume = 270 ÷ 100.0 = 2.70 g/cm³, which matches aluminium.
  6. Errors: air bubbles stuck to the solid, splashing, parallax, a solid that absorbs water. A displacement (Eureka) can collecting the overflow is more precise for large objects.

14.4 Practice problems with answers

1. u = 0, a = 3.0 m/s², t = 5.0 s. Find s.

s = ½ × 3.0 × 5.0² = 37.5 m, so 38 m (2 s.f.).

2. A runner goes 400 m round a track and finishes on the start line. Distance and displacement?

Distance 400 m, displacement 0 m.

3. Walk 6.0 m east, then 8.0 m north. Find the displacement.

√(6.0² + 8.0²) = 10 m on a bearing of 36.9° (north of east by 53.1°).

4. A car slows from 72 km/h to rest in 4.0 s. Find s.

u = 72 ÷ 3.6 = 20 m/s. s = ½(20 + 0)(4.0) = 40 m.

5. A stone is dropped from rest for 2.0 s (g = 9.8 m/s²). How far does it fall?

s = ½ × 9.8 × 2.0² = 19.6 m, so 20 m (2 s.f.).

6. From (−2, 4) m to (4, −4) m. Find |d|.

Δx = 6, Δy = −8, so |d| = 10 m.

7. v(t) = 4 − 2t m/s from 0 to 4 s. Displacement and distance?

s = [4t − t²] from 0 to 4 = 0 m. v = 0 at 2 s, so distance = 4 + 4 = 8 m.

8. Bore 3.50 in, stroke 3.50 in, 6 cylinders. Find the cubic inch displacement.

π/4 × 3.50² × 3.50 × 6 = 202 in³ (3.31 L).

9. A 54.0 g stone raises water from 30.0 mL to 50.0 mL. Find its density.

V = 20.0 cm³, ρ = 54.0 ÷ 20.0 = 2.70 g/cm³.

10. Trap: u = 20 m/s, a = −5.0 m/s². Does the car reach a wall 50 m away?

v² = 400 − 500 = −100, which is impossible. The car stops after s = 400 ÷ 10 = 40 m, 10 m short of the wall.

14.5 Mistakes that lose marks

  • Giving a distance when the question asks for displacement, or the other way round.
  • Leaving speeds in km/h. Divide by 3.6 before using any equation.
  • Dropping the minus sign on a deceleration or on a downward displacement.
  • Adding the sizes of two perpendicular displacements (3 + 4 = 7) instead of using Pythagoras (5).
  • Using the radius instead of the diameter in the engine formula, which gives an answer four times too big.
  • Forgetting the direction of a 2D displacement. A vector needs a size and a direction.
  • Writing a final answer with no unit, or with more significant figures than the data.

🎯 15. When to Use Each Displacement Equation

Use the SUVAT equations when:

  • ✓ The acceleration is constant (including free fall with no air resistance).
  • ✓ The motion is along one straight line.
  • ✓ You know three of s, u, v, a and t.

Use something else when:

  • ✗ The acceleration changes: integrate v(t), or find the area under a measured v-t graph.
  • ✗ The motion is in 2D or 3D with known positions: subtract the coordinates (Two Points mode).
  • ✗ The trip has several straight legs: add them as vectors (Distance vs Displacement mode).
  • ✗ Air resistance matters, as for a skydiver: SUVAT overestimates the fall. Use a drag model.
  • ✗ You need the volume an engine sweeps: that is engine displacement, a volume, not a length.

Real examples:

  1. Braking distance of a car from a speed and a deceleration: SUVAT, v² = u² + 2as.
  2. A hiker's GPS track of several legs: path mode, distance vs displacement.
  3. A robot arm moving between two points in 3D: two-points mode.
  4. A data logger that gives v(t) as a formula: calculus mode.
  5. Buying a motorbike and comparing 125 cc with 150 cc: engine mode.
  6. Identifying a metal in a school lab: water displacement density mode.
Decision tree. Is it a volume (engine or water)? Use those modes. Is it a change of position? If you know positions, subtract them. If you know legs, add them as vectors. If you know velocity: constant acceleration → SUVAT; changing acceleration → integrate v(t).

🔧 16. Common Mistakes and Troubleshooting

My answer is 3.6 times too big or too small

Cause: a speed left in km/h. Fix: choose km/h in the unit list beside the box, or divide by 3.6 yourself before typing.

The calculator says the displacement is never reached

Cause: u² + 2as is negative, so the object stops and turns round before it gets there. Fix: nothing is wrong with the tool. Check the sign of a. A braking car with a = −5 m/s² from 20 m/s stops after 40 m.

The sign of my answer is wrong

Cause: mixed directions. Fix: choose one positive direction and stick to it. For something thrown up, if up is positive then g is −9.8 m/s².

Distance and displacement came out different

Cause: the object turned round, or the path bent. Fix: this is correct physics. Read the distance row of the results table for the total path length.

My textbook answer is slightly different

Cause: a different g (9.8, 9.81 or 10) or rounding in the middle. Fix: set the g selector to your book's value and only round at the end.

My angle is off by 180°

Cause: tan−1(Δy/Δx) cannot tell (6, 8) from (−6, −8). Fix: use atan2, as this calculator does, or add 180° when Δx is negative.

My engine size is four times too big

Cause: the radius was used as if it were the diameter, or πr² was used with the diameter. Fix: bore is a diameter, so area = π/4 × bore².

My engine size is 1000 times off

Cause: bore and stroke in mm give mm³. Fix: divide mm³ by 1000 for cc, or pick mm in the unit list and let the tool convert.

My density is impossibly large

Cause: grams typed with the kg unit selected, or millilitres read as litres. Fix: match the unit list to what you typed. Nothing is denser than about 22.6 g/cm³.

The v(t) box shows an error

Cause: a missing operator or bracket, or a function undefined in the interval (such as 1/(t − 1) at t = 1). Fix: write 3*t^2 or 3t^2, close every bracket, and keep the interval away from division by zero.

Excel shows #NUM! or #VALUE!

Cause: a square root of a negative (#NUM!) or a unit typed into a cell (#VALUE!). Fix: see Section 9.6.

The charts do not appear

Cause: the chart library was blocked, or Calculate has not been pressed. Fix: press Calculate. The answer, steps, table and live diagram still work without the charts.

⚖ 17. Assumptions and Limitations

Assumptions

  1. Constant acceleration (SUVAT mode). Check that a does not change during the motion. If a really falls with time, as for a car easing off, SUVAT with the starting a overestimates the displacement.
  2. No air resistance. Check that speeds are low or objects are dense. When drag matters, SUVAT overestimates the displacement of a falling object: 490 m against about 340 m for a skydiver after 10 s.
  3. Straight-line motion in SUVAT. Check that the path does not curve. For curved paths, use the vector modes.
  4. Flat ground for paths. Legs are added on a flat map. Over hundreds of kilometres the curved Earth makes the flat-map displacement slightly too large.
  5. Perfect cylinders for engines. The formula gives swept volume only. It ignores the combustion chamber, so it underestimates the total cylinder volume, and badge figures are rounded.
  6. Fully submerged, non-absorbing solid for density. Air bubbles make the volume too large and the density too small. A solid that soaks up water makes the volume too small and the density too large.
  7. Exact numerical integration. Simpson's rule is exact for polynomials up to cubic. For sharp or very fast-changing functions it may carry a tiny error in the last digit.

Limitations

  • It does not model drag. For falling objects with air resistance, a drag model is needed.
  • It does not do relativistic motion. At speeds near light speed (above about 0.1c) Newtonian kinematics fails.
  • It does not handle rotating reference frames or the Coriolis effect.
  • The engine mode assumes 100% volumetric efficiency for air flow. Real engines fill about 80 to 95% of their swept volume.
  • The density match only suggests a material. Alloys and mixtures can share a density.
  • It is not for single displacement reactions in chemistry. Those are about atoms swapping places, not about distance; see the stoichiometry tool in Section 21.

🏁 18. Conclusion

___ Your own result appears here after you press Calculate.

What the answer is

A displacement calculator gives the straight-line change in position, with its direction, in metres. For the worked car problem it is 36 m forward. For an engine it gives a volume instead: 1998 cc for the 86.0 mm × 86.0 mm four-cylinder. For a solid in water it gives the volume that leads to density: 2.70 g/cm³ for the aluminium block.

What it means physically

Displacement compares only the start and the end. That is why it can be zero after a long journey, and why it is always shorter than or equal to the distance. The difference between the two tells you how much the path bent or doubled back. On a velocity-time graph the displacement is the net area under the line, which is also what integration measures.

Watch out for

Units (km/h, mm, grams typed as kilograms), signs (pick a positive direction), and the g your exam board uses. For engines, remember the bore is a diameter. For angles, use atan2 or check the quadrant.

Next steps

Divide displacement by time to get velocity with the velocity calculator, then find how quickly that velocity changes with the acceleration calculator. Fit a lab s-t² graph with linear regression. Come back to this displacement calculator whenever you need a displacement, a distance or an engine size with every step shown.

❓ 19. Frequently Asked Questions

What is a displacement calculator?

A displacement calculator finds the change in position of an object, final position minus initial position, with its direction. This one also finds distance travelled, works from the SUVAT equations, two points, a path or v(t), and calculates engine displacement in cc, litres and cubic inches.

How do you calculate displacement?

Subtract the starting position from the final position: Δx = x2 − x1. If you know motion values instead, use s = ut + ½at². A car at 5.0 m/s accelerating at 2.0 m/s² for 4.0 s has a displacement of 36 m.

What is the formula for displacement in physics?

The basic formula is Δx = x2 − x1. With constant acceleration the main formula is s = ut + ½at², along with s = ½(u + v)t and v² = u² + 2as. With a changing velocity, displacement is the integral of v(t) over time.

How do you calculate displacement with velocity and time?

Multiply the average velocity by the time: s = ½(u + v)t. At a constant velocity this is just s = vt, so 12 m/s for 5.0 s gives 60 m.

How do you calculate displacement with acceleration and time?

Use s = ut + ½at². From rest it becomes s = ½at², so a stone dropped for 3.00 s falls ½ × 9.81 × 3.00² = 44.1 m, ignoring air resistance.

What is the difference between distance and displacement?

Distance is the total length of the path and has no direction; displacement is the straight-line change in position and has a direction. Walking 3 km north then 4 km east is a distance of 7 km but a displacement of 5 km.

Can displacement be negative?

Yes. In one dimension a negative displacement means the object ended up on the negative side of its starting point. Distance can never be negative.

Can displacement be zero when distance is not?

Yes. Whenever an object returns to its starting point the displacement is zero. One lap of a 400 m track has a distance of 400 m and a displacement of 0 m.

How do you calculate displacement between two points?

Find the change in each coordinate and combine them with Pythagoras: |d| = √(Δx² + Δy² + Δz²). From (2, 3) m to (8, 11) m, Δx = 6 and Δy = 8, so the displacement is 10 m at 53.13° to the x axis.

How do you find displacement from a velocity-time graph?

Find the area between the graph and the time axis. Area above the axis is positive displacement and area below is negative. A line from 5 m/s to 13 m/s over 4 s encloses a trapezium of area 36 m.

How do you calculate displacement using calculus?

Integrate the velocity function over the time interval: s = ∫ v(t) dt. For v = 3t² − 12t + 9 from 0 to 4 s, the displacement is 4 m. Integrating |v(t)| instead gives the distance, 12 m.

How do you calculate engine displacement?

Multiply the piston area by the stroke and by the number of cylinders: V = π/4 × bore² × stroke × cylinders. An 86.0 mm bore and 86.0 mm stroke with four cylinders gives 1998 cc, sold as a 2.0 L engine.

How do you calculate engine displacement in cc?

Put the bore and stroke in centimetres into V = π/4 × b² × s × n, because 1 cm³ is exactly 1 cc. With millimetres, divide the answer by 1000. Divide cc by 1000 for litres.

How do you calculate cubic inch displacement?

Use the same formula with bore and stroke in inches: V = 0.7854 × bore² × stroke × cylinders. A V8 with a 4.000 in bore and 3.480 in stroke gives 349.8 cubic inches, the classic "350". To convert, divide cc by 16.387064.

How do you calculate density with water displacement?

Subtract the starting water level from the level with the object in to get its volume, then divide the mass by that volume. A 270 g block that raises water from 50.0 mL to 150.0 mL has a density of 270 ÷ 100.0 = 2.70 g/cm³.

What is the SI unit of displacement?

The SI unit of displacement is the metre (m), the same as distance. Engine displacement is a volume, measured in cubic centimetres (cc), litres or cubic inches.

How do you calculate displacement in Excel?

Type the SUVAT formula into a cell: with u in B2, a in C2 and t in D2, use =B2*D2+0.5*C2*D2^2. For two points use =SQRT((C2-A2)^2+(D2-B2)^2), and for engine cc from millimetres use =PI()/4*B2^2*C2*D2/1000.

How do you calculate displacement in Python?

Write s = u*t + 0.5*a*t**2, using ** for powers. For two points use numpy.linalg.norm(p2 - p1), and for a velocity function integrate it with scipy.integrate.quad. Section 11 has a complete script that saves a 300 dpi graph.

How do you calculate displacement in R?

Write s <- u * t + 0.5 * a * t^2 in base R. For two points use sqrt(sum((p2 - p1)^2)), and for v(t) use integrate(). Section 10 has a complete script with a check and a 300 dpi graph.

How do you calculate displacement on a scientific calculator?

Type the whole expression in one line: 5 × 4 + 0.5 × 2 × 4 x² = gives 36. For angles, set the calculator to DEG mode first. Store values in memories if you reuse them, and round only the final answer.

📑 20. Cite This Tool

APA 7th edition
StatsUnlock Team. (2026). Displacement calculator [Interactive physics tool]. StatsUnlock. https://statsunlock.com/displacement-calculator/
BibTeX
@misc{statsunlock_displacement_2026, title={Displacement Calculator}, author={{StatsUnlock Team}}, year={2026}, publisher={StatsUnlock}, note={Interactive physics tool}, url={https://statsunlock.com/displacement-calculator/}}
Methods wording
Displacement was calculated with the StatsUnlock Displacement Calculator (2026) using the constant-acceleration equations, with every input converted to SI units, standard gravity g = 9.80665 m/s², and each answer verified by substitution into a second equation. Engine displacement was calculated as V = π/4 × bore² × stroke × number of cylinders.

📖 22. Glossary of Terms

TermPlain-English meaning
Acceleration (a)How fast the velocity changes, in m/s².
Archimedes' principleA submerged object is pushed up by a force equal to the weight of liquid it displaces, in N.
BearingA direction measured clockwise from north, in degrees.
BoreThe diameter of an engine cylinder, in mm or in.
Compression ratioTotal cylinder volume divided by the chamber volume. No unit.
Cubic centimetre (cc)1 cm³, the usual unit for engine size. 1000 cc = 1 L.
Cubic inch (in³, CID)16.387064 cc, used for US engine sizes.
Density (ρ)Mass per unit volume, in g/cm³ or kg/m³.
DisplacementChange in position, final minus initial, with a direction, in m.
DistanceTotal length of the path travelled, never negative, in m.
Engine displacementTotal volume swept by all the pistons, in cc, L or in³.
Free fallMotion under gravity alone, with a = g, about 9.81 m/s² on Earth.
GRESSGiven, Required, Equation, Substitute, Solve: the layout examiners expect.
IntegralThe area under a curve. The integral of v(t) is the displacement, in m.
MagnitudeThe size of a vector without its direction.
PositionWhere an object is relative to a chosen origin, in m.
ScalarA quantity with size only, such as distance or speed.
SpeedDistance divided by time, in m/s. Never negative.
StrokeHow far the piston travels from top to bottom of the cylinder, in mm or in.
SUVATThe five constant-acceleration quantities s, u, v, a, t and their equations.
Swept volumeThe volume one piston moves through in one stroke, in cc.
VectorA quantity with size and direction, such as displacement or velocity.
Velocity (v)Displacement divided by time, with a direction, in m/s.

📚 23. References

Peer-reviewed sources for the physics, the teaching methods and the engine and density content of this displacement calculator. Every DOI was checked in October 2026.

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  2. Christensen, W. M., & Thompson, J. R. (2012). Investigating graphical representations of slope and derivative without a physics context. Physical Review Special Topics - Physics Education Research, 8(2), 023101. https://doi.org/10.1103/PhysRevSTPER.8.023101
  3. Fraser, N., Blaxill, H., Lumsden, G., & Bassett, M. (2009). Challenges for increased efficiency through gasoline engine downsizing. SAE International Journal of Engines, 2(1), 991–1008. https://doi.org/10.4271/2009-01-1053
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  5. Halloun, I. A., & Hestenes, D. (1985). The initial knowledge state of college physics students. American Journal of Physics, 53(11), 1043–1055. https://doi.org/10.1119/1.14030
  6. Hestenes, D., Wells, M., & Swackhamer, G. (1992). Force concept inventory. The Physics Teacher, 30(3), 141–158. https://doi.org/10.1119/1.2343497
  7. Hughes, S. W. (2005). Archimedes revisited: A faster, better, cheaper method of accurately measuring the volume of small objects. Physics Education, 40(5), 468–474. https://doi.org/10.1088/0031-9120/40/5/008
  8. McDermott, L. C. (1991). Millikan Lecture 1990: What we teach and what is learned. Closing the gap. American Journal of Physics, 59(4), 301–315. https://doi.org/10.1119/1.16539
  9. McDermott, L. C., Rosenquist, M. L., & van Zee, E. H. (1987). Student difficulties in connecting graphs and physics: Examples from kinematics. American Journal of Physics, 55(6), 503–513. https://doi.org/10.1119/1.15104
  10. Nguyen, D.-H., & Rebello, N. S. (2011). Students' understanding and application of the area under the curve concept in physics problems. Physical Review Special Topics - Physics Education Research, 7(1), 010112. https://doi.org/10.1103/PhysRevSTPER.7.010112
  11. Nguyen, N.-L., & Meltzer, D. E. (2003). Initial understanding of vector concepts among students in introductory physics courses. American Journal of Physics, 71(6), 630–638. https://doi.org/10.1119/1.1571831
  12. Planinic, M., Ivanjek, L., Susac, A., & Milin-Sipus, Z. (2013). Comparison of university students' understanding of graphs in different contexts. Physical Review Special Topics - Physics Education Research, 9(2), 020103. https://doi.org/10.1103/PhysRevSTPER.9.020103
  13. Rosenblatt, R., & Heckler, A. F. (2011). Systematic study of student understanding of the relationships between the directions of force, velocity, and acceleration in one dimension. Physical Review Special Topics - Physics Education Research, 7(2), 020112. https://doi.org/10.1103/PhysRevSTPER.7.020112
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  17. Tiesinga, E., Mohr, P. J., Newell, D. B., & Taylor, B. N. (2021). CODATA recommended values of the fundamental physical constants: 2018. Reviews of Modern Physics, 93(2), 025010. https://doi.org/10.1103/RevModPhys.93.025010
  18. Trowbridge, D. E., & McDermott, L. C. (1980). Investigation of student understanding of the concept of velocity in one dimension. American Journal of Physics, 48(12), 1020–1028. https://doi.org/10.1119/1.12298
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  20. Turner, J. W. G., Popplewell, A., Patel, R., Johnson, T. R., Darnton, N. J., Richardson, S., Bredda, S. W., Tudor, R. J., Bithell, C. I., Jackson, R., Remmert, S. M., Cracknell, R. F., Fernandes, J. X., Lewis, A. G. J., Akehurst, S., Brace, C. J., Copeland, C., Martinez-Botas, R., Romagnoli, A., & Burluka, A. A. (2014). Ultra boost for economy: Extending the limits of extreme engine downsizing. SAE International Journal of Engines, 7(1), 387–417. https://doi.org/10.4271/2014-01-1185
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