# Explain why the total mechanical energy of an object undergoing simple harmonic motion remains constant, and describe how the kinetic and potential energies vary during one complete oscillation.

> IB DP Physics Standard Level (2023 syllabus) — C.1 Simple harmonic motion · Explain · 4 marks

> An object of mass m oscillates on a frictionless horizontal surface, attached to a spring. The object passes through the equilibrium position with maximum speed and momentarily comes to rest at the amplitude positions.

## Mark scheme (4 marks)

1. In the absence of friction (or other dissipative forces), no energy is transferred to the surroundings, so total mechanical energy is conserved/constant.
2. At the equilibrium position, displacement is zero so potential energy is at a minimum (zero), and kinetic energy is at a maximum.
3. At the amplitude (maximum displacement) positions, the velocity is zero so kinetic energy is zero/minimum, and potential energy is at a maximum.
4. During the oscillation, energy is continuously and repeatedly converted between kinetic and potential forms such that their sum (total mechanical energy) remains constant throughout.

## Key terms

- [simple harmonic motion](https://www.gradenine.co.uk/glossary/simple-harmonic-motion)
- [total mechanical energy](https://www.gradenine.co.uk/glossary/total-mechanical-energy)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-total-mechanical-energy-26950ccf) · Published by Druglandscape Ltd.