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Vibrations

Displacement and velocity graphs

  • 3 things to know
  • Component 1

Overview

Recall questions on the shapes of the displacement, velocity and acceleration graphs and their quarter-cycle phase relationships, obtaining velocity as the gradient of the displacement graph, and where on each the gradient is greatest and where zero.

What you need to know

Answer each one before you reveal it.

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Key term

What quantity is given by the gradient of a displacement-time graph for an oscillator?

Key term

What quantity is given by the gradient of a velocity-time graph for an oscillator?

Key term

State the phase difference between the displacement-time and velocity-time graphs of a simple harmonic oscillator.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe the shape of a displacement-time graph for a simple harmonic oscillator released from maximum displacement.

    Model answer

    The graph is a cosine curve starting at the amplitude, falling through zero to minus the amplitude and returning, repeating with the period of the oscillation.

  2. 2

    Describe the shape of a velocity-time graph for a simple harmonic oscillator released from maximum displacement.

    Model answer

    The graph is a negative sine curve, starting at zero, falling to minus the maximum speed after a quarter period and returning through zero at the half period.

  3. 3

    What quantity is given by the gradient of a displacement-time graph for an oscillator?

    Model answer

    The gradient of a displacement-time graph gives the velocity of the oscillator at that instant.

  4. 4

    What quantity is given by the gradient of a velocity-time graph for an oscillator?

    Model answer

    The gradient of a velocity-time graph gives the acceleration of the oscillator at that instant.

  5. 5

    State the phase difference between the displacement-time and velocity-time graphs of a simple harmonic oscillator.

    Model answer

    The two are a quarter of a cycle out of step, a phase difference of π/2 radians, with the velocity ahead of the displacement.

  6. 6

    State the phase difference between the displacement-time and acceleration-time graphs of a simple harmonic oscillator.

    Model answer

    The two are exactly out of phase, a phase difference of π radians, since the acceleration is −ω² times the displacement at every instant.

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