Displacement in SHM follows x = Acos(2pift) or x = Asin(2pift) depending on initial conditions. Velocity and acceleration are also sinusoidal but shifted in phase. Velocity is zero at the turning points (x = plus or minus A) and maximum at equilibrium (x = 0). Acceleration is maximum in magnitude at the turning points and zero at equilibrium, always pointing opposite to displacement. On a graph, the x-t, v-t, and a-t curves all have the same period but peak at different times. Changing amplitude stretches the curves vertically but does not change the period or the horizontal spacing of the peaks and zeros.
- x = A*cos(2*pi*f*t): Displacement equation for an oscillator starting at maximum positive displacement; A is amplitude and f is frequency.
- Turning points: Positions x = plus or minus A where velocity is zero and acceleration (and restoring force) is maximum in magnitude.
- Equilibrium crossing: Position x = 0 where speed is maximum and acceleration is zero; the object passes through fastest here.
- Phase relationship: Velocity peaks one quarter cycle after displacement crosses zero; acceleration is always opposite in sign to displacement.
- Amplitude vs. period: Increasing amplitude raises the maximum values of displacement, velocity, and acceleration but leaves the period unchanged.
An object in SHM has displacement x = 0.05cos(4pi*t) meters. At t = 0, what are the displacement, velocity direction, and acceleration direction?
| Quantity | At x = +A (turning point) | At x = 0 (equilibrium) |
|---|
| Displacement | Maximum positive | Zero |
| Speed | Zero | Maximum |
| Acceleration magnitude | Maximum | Zero |
| Restoring force magnitude | Maximum | Zero |