MEPX
Chapter 3 of 13All chapters
  1. 1What physics is
  2. 2Units and measurement
  3. 3Describing motion
  4. 4The laws of motion
  5. 5Forces
  6. 6Energy and work
  7. 7Momentum and collisions
  8. 8Waves
  9. 9Sound
  10. 10Light and optics
  11. 11Electricity and magnetism
  12. 12Heat and thermodynamics
  13. 13Modern physics

Chapter 3 of 13

Describing motion

Speed, velocity and acceleration.

Three quantities

Speed is how fast. Velocity is how fast in a direction. Acceleration is how quickly velocity changes, which includes slowing down and turning.

  • A car going round a bend at constant speed is accelerating, because the direction changes.
  • Distance is the ground covered; displacement is the straight line from start to finish.

Graphs

On a distance against time graph the slope is speed. On a velocity against time graph the slope is acceleration and the area underneath is distance.