3.6.1.1
Angular displacement is measured in radians
Circular Motion — AQA A-Level Physics
Key Definition
Radian — The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.
$$\Delta \theta = \frac{\Delta s}{r}$$
- $\Delta \theta$: angular displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m). (rad)
- $\Delta s$: arc length (m)
- $r$: radius of circle (m)
- A full $circle = 2pi rad = 360 degrees$.
- To convert degrees to radians: multiply by pi/180.
- To convert radians to degrees: multiply by 180/pi.
- 1 radianThe angle subtended at the centre of a circle by an arc equal in length to the radius. One complete revolution = 2π radians. is approximately 57.3 degrees.
Examiner Tips and Tricks
- Check your calculator is in radians mode (look for the 'R' at the top of the screen) when using sin, cos, or tan with angular frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz)..
- This is one of the most common mark-losing errors in the entire exam.