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Motion Basics

Physics: IB Diploma Higher Level, topic 1.1.1

Key Concepts of Motion

Displacement, speed, velocity and acceleration are fundamental concepts when describing motion in a straight line. You need to know how they link together.

Displacement

Displacement

  • The displacement of an object, s, is the distance and direction from an object's starting position to its final position.
Velocity and speed

Velocity and speed

  • The velocity of an object, v, is the speed and direction an object is travelling.
  • It is the rate of change of displacement:
  • v=ΔsΔtv = \frac{\Delta s}{\Delta t}
  • Speed is the magnitude of the velocity.
  • Instantaneous speed/velocity is the speed/velocity of an object at a given instant in time.
  • Average speed/velocity is the total distance/displacement divided by the total time taken.
Acceleration

Acceleration

  • The acceleration of an object, a, is the rate (and direction) at which its velocity changes:
  • a=ΔvΔta = \frac{\Delta v}{\Delta t}
Delta symbol

Delta symbol

  • Delta, Δ, is the symbol meaning "change in".
  • For example, Δs means change in displacement.

Test yourself on Motion Basics

  • What does s represent?

  • What is the correct formula for acceleration?

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