3.6.1.2
The displacement, velocity, and acceleration graphs are 90 degrees out of phase
Simple Harmonic Motion — AQA A-Level Physics
- If displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m). is a cosine curve, velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹. is a negative sine curve (90 degrees ahead).
- AccelerationThe rate of change of velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. A vector quantity. Measured in m s⁻². is a negative cosine curve (180 degrees ahead of displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m)., i.e. a reflection in the time axis).
- VelocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹. is the gradient of the displacementThe distance moved in a particular direction from a starting point. A vector quantity. Measured in metres (m).-time graph.
- AccelerationThe rate of change of velocity. A vector quantity. Measured in m s⁻². is the gradient of the velocity-time graph.
Key graph relationships
- When displacement is maximum, velocity is zero and accelerationThe rate of change of velocity. A vector quantity. Measured in m s⁻². is maximum (in the opposite direction).
- When displacement is zero, velocity is maximum and acceleration is zero.
- The acceleration graph is a reflection of the displacement graph in the x-axis. This follows directly from $a = -\omega^2 x$.
Examiner Tips and Tricks
- The time periodThe time taken for one complete oscillation or wave cycle. Measured in seconds (s). can be read from any of the three graphs.
- Look for the time between two identical points on the curve (e.g. peak to peak).
- Velocity is at its maximum when the displacement curve crosses zero.