Angular displacement, velocity and acceleration

Overview

Angular motion and eccentric force, angular displacement, velocity and acceleration with worked discus and skater examples, radians, and the diver's take-off.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is angular motion?

   Model answer

   Angular motion is movement of a body or body part around an axis of rotation. A gymnast's somersault is an example.

2. 2

   What causes angular motion?

   Model answer

   Angular motion is caused by an eccentric force, which acts outside the centre of mass. The force creates a turning effect called torque.

3. 3

   What is angular displacement?

   Model answer

   Angular displacement is the smallest change in angle between the start and finish positions of a rotating body. The unit is the radian.

4. 4

   What is angular velocity?

   Model answer

   Angular velocity is the rate of change of angular displacement. The unit is radians per second (rad s⁻¹).

5. 5

   A discus thrower's arm turns through 6.28 rad in 0.5 s. What is the average angular velocity?

   Model answer

   The average angular velocity is about 12.6 rad s⁻¹. The working is 6.28 rad ÷ 0.5 s = 12.56 rad s⁻¹.

6. 6

   What is angular acceleration?

   Model answer

   Angular acceleration is the rate of change of angular velocity. The unit is radians per second squared (rad s⁻²).

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