## AQA A Level Physics

### Revision Notes

• In circular motion, it is more convenient to measure angular displacement in units of radians rather than units of degrees
• The angular displacement (θ) of a body in circular motion is defined as:

The change in angle, in radians, of a body as it rotates around a circle

• The angular displacement is the ratio of: • Note: both distances must be measured in the same units e.g. metres

The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle

• Angular displacement can be calculated using the equation: • Where:
• Δθ = angular displacement, or angle of rotation (radians)
• s = length of the arc, or the distance travelled around the circle (m)
• r = radius of the circle (m)

• Radians are commonly written in terms of π
• The angle in radians for a complete circle (360o) is equal to: • If an angle of 360o = 2π radians, then 1 radian in degrees is equal to: • Use the following equation to convert from degrees to radians: #### Worked Example

Convert the following angular displacement into degrees:  #### Exam Tip

• This is shown by the “D” or “R” highlighted at the top of the screen
• Remember to make sure it’s in the right mode when using trigonometric functions (sin, cos, tan) depending on whether the answer is required in degrees or radians
• It is extremely common for students to get the wrong answer (and lose marks) because their calculator is in the wrong mode – make sure this doesn’t happen to you! Close Close