AdvancedTopic 73 of 106Engineering Mechanics

Simple harmonic motion

Restoring force proportional to displacement gives sinusoidal motion x=A cos(ωt).

In depth

SHM satisfies x''=-ω²x with solution x=A cos(ωt+φ). Period T=2π/ω, frequency f=1/T. Energy exchanges between kinetic and potential with total ½kA². Appears in pendulums, springs and electrical LC circuits.

Key points

  • Restoring force proportional to displacement
  • Amplitude independent of frequency
  • Phase from initial conditions
Example

A pendulum with L=1 m has T≈2 s for small angles.

Why it matters

Simple harmonic motion is the model for small oscillations, so it underlies pendulums, springs and many acoustic and electrical resonances.

Where this is used

  • Modelling a small swing of a pendulum clock.
  • Describing the motion of a mass on a spring used as a sensor.
  • Analysing the small oscillation of a moored buoy.

Frequently asked questions

What is Simple harmonic motion?

Restoring force proportional to displacement gives sinusoidal motion x=A cos(ωt).

Why is it important to understand simple harmonic motion?

Simple harmonic motion is the model for small oscillations, so it underlies pendulums, springs and many acoustic and electrical resonances.

What makes motion simple harmonic?

A restoring force that is proportional to displacement and acts toward equilibrium, which gives a sinusoidal solution in time.

Why do pendulums stop being harmonic at large angles?

The restoring torque is then proportional to sine of the angle rather than the angle itself, so the period depends on amplitude.

How is Simple harmonic motion used in practice?

Typical applications include modelling a small swing of a pendulum clock, describing the motion of a mass on a spring used as a sensor and analysing the small oscillation of a moored buoy.

What should I learn before Simple harmonic motion?

Study "Residual stress" first (topic 72 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.

What are the key points of Simple harmonic motion?

Restoring force proportional to displacement. Amplitude independent of frequency. Phase from initial conditions.

Can you give an example of Simple harmonic motion?

A pendulum with L=1 m has T≈2 s for small angles.

What comes after Simple harmonic motion?

The next topic is "Mass-spring system", which builds directly on this one.

How difficult is Simple harmonic motion?

It is classed as Advanced in Engineering Mechanics (topic 73 of 106). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Engineering Mechanics.

Learning path

Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.

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