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Circular Motion

Period and frequency of rotation

  • 3 things to know
  • Component 1

Overview

Period of rotation of a body moving in a circle, frequency of rotation and unit of frequency and express it in SI base units.

What you need to know

Answer each one before you reveal it.

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Key term

Explain why a body in uniform circular motion has a constant speed but a changing velocity.

Key term

Define the period of rotation of a body moving in a circle.

Key term

Define the frequency of rotation.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define the period of rotation of a body moving in a circle.

    Model answer

    The period of rotation is the time taken for the body to complete one full revolution.

  2. 2

    Define the frequency of rotation.

    Model answer

    The frequency of rotation is the number of complete revolutions made per unit time.

  3. 3

    State the unit of frequency and express it in SI base units.

    Model answer

    Frequency is measured in hertz, and one hertz is one per second, s⁻¹.

  4. 4

    State the relationship between period and frequency.

    Model answer

    The period is the reciprocal of the frequency, so T = 1/f with T in s and f in Hz.

  5. 5

    A record turntable rotates at 45 revolutions per minute. Calculate its frequency and period of rotation.

    Model answer

    The frequency is 45 ÷ 60 = 0.75 Hz and the period is 1 ÷ 0.75 = 1.3 s. Multiplying 0.75 Hz by 60 s returns 45 revolutions.

  6. 6

    A wheel makes 5.0 complete turns every second. State its frequency and calculate its period.

    Model answer

    The frequency is 5.0 Hz and the period is 1 ÷ 5.0 = 0.20 s. Multiplying 0.20 s by 5.0 returns 1.0 s for five turns.

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