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A LevelPhysicsOCRRevision Notes5. Newtonian World & AstrophysicsSimple Harmonic OscillationsConditions for Simple Harmonic Motion

Conditions for Simple Harmonic Motion (OCR A Level Physics): Revision Note

Exam code: H556

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Katie M

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Simple Harmonic Motion

  • Simple harmonic motion (SHM) is a specific type of oscillation

  • An oscillation is said to be SHM when:

The acceleration of a body is proportional to its displacement, but acts in the opposite direction

  • Acceleration a and displacement x can be represented by the defining equation of SHM:

a space proportional to space minus x

  • The two conditions required for an object to be in simple harmonic motion are therefore:

    • The acceleration is proportional to the displacement

    • The acceleration is in the opposite direction to the displacement

SHM pendulum, downloadable AS & A Level Physics revision notes

Force, acceleration and displacement of a pendulum in SHM

Worked Example

Explain why a person jumping on a trampoline is not an example of simple harmonic motion.

Answer:

Step 1: Recall the conditions for simple harmonic motion

  • The conditions required for SHM:

    • The restoring force/acceleration is proportional to the displacement

    • The restoring force/acceleration is in the opposite direction to the displacement

Step 2: Consider the forces in the scenario given

  • When the person is not in contact with the trampoline, the restoring force is equal to their weight, which is constant

  • The value of their weight does not change, even if they jump higher (increase displacement)

Step 3: Write a concluding sentence

  • The restoring force on the person is not proportional to their distance from the equilibrium position, therefore, this scenario does not fulfil the conditions for SHM

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    Author: Katie M

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