Damping is when a spring, swing, or other vibrating object loses its energy over time. It means that without adding energy into the system, like pumping on a swing or hitting a drum head, the object will eventually come to its non-vibrating (equilibrium) position.

Imagine the kid on the swing again. Why does the kid move past the equilibrium point without stopping?
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It’s actually because of Newton’s law of inertia. The swing continues on its path as long as there are balanced forces acting on it. As the swing moves past its equilibrium point, a restoring force acts on it to move it back to its original equilibrium position.

The difference between a vibration (like a kid swinging) and translational motion (like a kid on roller skates) is that the kid on skates can be permanently displaced from his starting position. The kid on a swing doesn’t move away from its original equilibrium position for long – it stops, turns around, and comes back due to the restoring force. An object that vibrates actually wiggles and jiggles around a fixed position (the equilibrium position).

Other examples of vibrating objects include tuning forks (which are like inverted swings), piano strings, car suspension systems,  a weight on the end of a spring that bobs up and down, and drum heads. In each of these examples, when the object is disturbed (like hitting the tuning fork or drum head, or pulling the weight at the end of the spring), the object moves from its original resting position, stops and heads back toward its resting position and overshoots, stops and come back toward the resting position and the cycle repeats. The object moves along the same path over and over again, and if there was no friction or drag force (or other energy losses), the object would continue to move back and forth forever.

Did you notice that when you graph out the motion of the mass on a spring, it has a particular shape? The shape is described in math as a sinusoidal wave, or y = sin(x).  Did you notice how it is periodic and that you could also see the damping effect? The damping effect means that energy is being lost or dissipated. (Scientists wouldn’t say that it’s slowing down, because that indicates that the speed is decreasing, which isn’t the case when the mass stops and turns around to head back to the resting position.. it is actually speeding up!)

Click here to go to next lesson on Frequency.

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