weirdfacts
Year 11 / Linear motion and force

Read motion from a slope.

Displacement is a vector from initial to final position; distance adds the lengths of the path travelled. Average velocity is displacement divided by elapsed time. Velocity is the gradient of a position–time graph, and acceleration is the gradient of a velocity–time graph.

The signed area under velocity versus time gives displacement. Areas below the axis contribute negatively. Add absolute areas to find distance. A curved position graph can represent acceleration even if every position value is positive.

INTERACTIVE MODEL

Velocity and acceleration

READ THE GRAPH

Explore the relationship

Initial velocity +3 m s⁻¹; constant acceleration. The graph area gives signed displacement.

Velocity / m s⁻¹02.8885.7758.66311.5502468Time / s
Velocity / m s⁻¹

Tap or focus a plotted point to read its values.

View plotted data as a table
Explore the relationship
SeriesTime / sVelocity / m s⁻¹
Velocity / m s⁻¹03
Velocity / m s⁻¹0.1333333.13333
Velocity / m s⁻¹0.2666673.26667
Velocity / m s⁻¹0.43.4
Velocity / m s⁻¹0.5333333.53333
Velocity / m s⁻¹0.6666673.66667
Velocity / m s⁻¹0.83.8
Velocity / m s⁻¹0.9333333.93333
Velocity / m s⁻¹1.066674.06667
Velocity / m s⁻¹1.24.2
Velocity / m s⁻¹1.333334.33333
Velocity / m s⁻¹1.466674.46667
Velocity / m s⁻¹1.64.6
Velocity / m s⁻¹1.733334.73333
Velocity / m s⁻¹1.866674.86667
Velocity / m s⁻¹25
Velocity / m s⁻¹2.133335.13333
Velocity / m s⁻¹2.266675.26667
Velocity / m s⁻¹2.45.4
Velocity / m s⁻¹2.533335.53333
Velocity / m s⁻¹2.666675.66667
Velocity / m s⁻¹2.85.8
Velocity / m s⁻¹2.933335.93333
Velocity / m s⁻¹3.066676.06667
Velocity / m s⁻¹3.26.2
Velocity / m s⁻¹3.333336.33333
Velocity / m s⁻¹3.466676.46667
Velocity / m s⁻¹3.66.6
Velocity / m s⁻¹3.733336.73333
Velocity / m s⁻¹3.866676.86667
Velocity / m s⁻¹47
Velocity / m s⁻¹4.133337.13333
Velocity / m s⁻¹4.266677.26667
Velocity / m s⁻¹4.47.4
Velocity / m s⁻¹4.533337.53333
Velocity / m s⁻¹4.666677.66667
Velocity / m s⁻¹4.87.8
Velocity / m s⁻¹4.933337.93333
Velocity / m s⁻¹5.066678.06667
Velocity / m s⁻¹5.28.2
Velocity / m s⁻¹5.333338.33333
Velocity / m s⁻¹5.466678.46667
Velocity / m s⁻¹5.68.6
Velocity / m s⁻¹5.733338.73333
Velocity / m s⁻¹5.866678.86667
Velocity / m s⁻¹69
Velocity / m s⁻¹6.133339.13333
Velocity / m s⁻¹6.266679.26667
Velocity / m s⁻¹6.49.4
Velocity / m s⁻¹6.533339.53333
Velocity / m s⁻¹6.666679.66667
Velocity / m s⁻¹6.89.8
Velocity / m s⁻¹6.933339.93333
Velocity / m s⁻¹7.0666710.0667
Velocity / m s⁻¹7.210.2
Velocity / m s⁻¹7.3333310.3333
Velocity / m s⁻¹7.4666710.4667
Velocity / m s⁻¹7.610.6
Velocity / m s⁻¹7.7333310.7333
Velocity / m s⁻¹7.8666710.8667
Velocity / m s⁻¹811
Velocity / m s⁻¹: 3

Explore: Adjust acceleration and compare the velocity slope with the moving marker.

vˉ=ΔxΔta=ΔvΔt\bar v=\frac{\Delta x}{\Delta t}\qquad a=\frac{\Delta v}{\Delta t}
WORKED EXAMPLE

A runner goes 30 m east, then 10 m west in 10 s.

  1. Distance = 40 m; displacement = 20 m east.
  2. Average speed = 4 ms1\mathrm{m}\,\mathrm{s}^{-1}; average velocity = 2 ms1\mathrm{m}\,\mathrm{s}^{-1} east.
Assumed knowledge

Signed numbers and triangle areas.

Learning checkpoints & sourceYOUR LEARNING CHECKPOINT
  • Distinguish distance, displacement, speed and velocity.
  • Use graph gradients and signed areas.
QCAA Physics · Unit 2 · Linear motion and force
READY TO TRY IT?

Put the idea to work.

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