What are Forced Vibrations?
- A forced vibration (oscillation) occurs when an external oscillating (periodic) force acts on a system.
- This may make it oscillate at a frequency which is different from the natural frequency.
- The most important examples of forced oscillations are those in which the frequency of the external force, which is called the driving frequency, is the same as the natural frequency.
- When regular periodic stimulus to a system results in an increasing amplitude, the effect is called resonance.
Example
- Imagine a parent pushing their child on a swing.
- If they push the swing when its amplitude is the highest, and velocity is zero, then their pushing will be resonant, and the swing will go higher next time.
- However, if they push before the swing is at its highest amplitude, they are pushing in the opposite direction of the motion, causing the swing to slow down.