3.1.2

Simple Harmonic Motion

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Simple Harmonic Motion (SHM)

SHM is any motion in which the acceleration is directed towards a fixed point (or equilibrium position for 1-D examples) AND is directly proportional to the negative of the displacement.

Formulae

Formulae

  • Mathematically, the definition of SHM can be expressed in a formula:
    • a=ω2xa=-\omega^2 x
      • a is the acceleration.
      • ω=2πf\omega = 2\pi f, where f is the frequency of oscillation
      • x is the displacement.
Acceleration-displacement graph

Acceleration-displacement graph

  • The acceleration-displacement graph is a straight-line graph that passes through the origin.
  • The angular frequency can be found from the gradient:
    • gradient =ω2= -\omega^2
    • ω=gradient\omega = \sqrt{-gradient}
Calculating maximum acceleration

Calculating maximum acceleration

  • If we are given the time period, T (or the frequency f), ω² can be calculated.
  • The maximum acceleration is given by:
    • amax=ω2Aa_{max}=\omega^2A
      • where A is the maximum displacement.

Simple Harmonic Motion (SHM) Graphs

SHM can be represented graphically.

Acceleration and displacement

Acceleration and displacement

  • The acceleration can be found graphically, and so the displacement or vice versa from a graph.
    • E.g. if you have a displacement-time graph, you can calculate the period and angular frequency.
  • The displacement at any point can be read off the graph. This means you can calculate the acceleration (and then even the net force) because a=ω2xa=-\omega^2 x.
Velocity and displacement

Velocity and displacement

  • The velocity at any given time is found from the gradient of a displacement-time graph.
  • By finding the gradient at each point in time, we can produce a velocity-time graph from a displacement-time graph.
Velocity and acceleration

Velocity and acceleration

  • In a similar way, you can use a velocity-time graph to get the corresponding acceleration-time graph. This is because the gradient at a point on any velocity-time graph gives the acceleration at that moment in time.
  • You can then see that the acceleration-time graph is exactly the same shape as the displacement-time graph, reflected in the x-axis.

Simple Harmonic Equations

The condition for simple harmonic motion is that the acceleration is directed towards a fixed point and that the magnitude of the acceleration is proportional to the negative of the displacement.

Oscillations

Oscillations

  • For SHM the acceleration must be proportional to the negative of the displacement. aαxa{\alpha}-x
  • If an object is under SHM it's displacement is found by x=Acos(ωt)x=A\cos({\omega}t) where A is the amplitude
  • The defining equation of SHM is a=ω2xa=-{\omega}^2x

Maximum points

  • The maximum displacement can be found when cos(ωt)=1\cos({\omega}t)=1
  • The maximum displacement is called the amplitude A
  • The maximum speed is given by v=ωAv={\omega}A
  • The maximum acceleration is given by a=ω2Aa={\omega}^2A
Jump to other topics
1

Space, Time & Motion

2

The Particulate Nature of Matter

3

Wave Behaviour

4

Fields

4.1

Circular Motion

4.2

Newton's Law of Gravitation

4.3

Fields

4.4

Fields at Work

4.5

Electric Fields

4.6

Magnetic Effect of Electric Currents

4.7

Heating Effect of Currents

4.8

Electromagnetic Induction

4.9

Power Generation & Transmission

4.10

Capacitance

5

Nuclear & Quantum Physics

6

Measurements

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