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Engineering Physics

Rotational motion

  • 6 things to know
  • Paper 3, section B

Overview

Angular displacement, velocity and acceleration, the rotational equations of motion, and the graphs.

What you need to know

Answer each one before you reveal it.

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Process

What is angular displacement, and how does angular speed differ from angular velocity?

Numbers

How is angular velocity calculated, what is angular acceleration, and how does angular speed differ from angular velocity?

Numbers

What do the gradients of the angular displacement and angular velocity graphs give?

Numbers

Why does the slope of an ω–t graph give angular acceleration, how is its instantaneous value found, and what does the area under the graph give?

Numbers

What does ω₂ = ω₁ + αt relate, and what do curved and straight graph lines indicate?

Numbers

When is ω₂² = ω₁² + 2αθ used, and what are the translational analogues?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define angular displacement.

    Model answer

    Angular displacement is the angle through which an object rotates about a fixed axis, measured in radians.

  2. 2

    What is the SI unit for angular displacement?

    Model answer

    Radians.

  3. 3

    How does angular speed differ from angular velocity?

    Model answer

    Angular speed is a scalar quantity (magnitude only), whereas angular velocity is a vector quantity with both magnitude and direction.

  4. 4

    Define angular velocity.

    Model answer

    Angular velocity is a vector quantity representing the rate of change of angular displacement, with direction along the axis of rotation determined by the right-hand rule.

  5. 5

    How is the direction of the angular velocity vector determined?

    Model answer

    Using the right-hand rule: if the fingers curl in the direction of rotation, the thumb points along the axis in the direction of the angular velocity vector.

  6. 6

    Define angular acceleration.

    Model answer

    Angular acceleration is the rate of change of angular velocity with respect to time.

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