David R. answered • 04/09/20
I'm a language buff pursuing a masters in engineering
I will answer based on the case of oscillating motion. There are other reasons for dampers too, follow up with me if you are curious.
Imagine you are holding a weight attached to a spring. If you make a sudden movement with your hand the weight will begin to bounce. For every weight and spring there is a specific frequency to the bounces. Let's say you observe the bouncing weight carefully so that you know this frequency. Let's call this the "natural frequency". Note: this frequency does not change as the weight bounces higher.
Now, make the same sudden movement with your hand, but continue to move your hand up and down with a steady frequency which is NOT the same as the "natural frequency". Sometimes you will pull the weight up when it is going down, thereby slowing it down. Sometimes you will pull it down faster speeding it up. It appears to fly all over the place as expected.
Lastly, lets say you are a robot and can move your hand up and down at exactly the "natural frequency". Once the weight begins to bounce you will always be "in sync". When it is travelling down, you pull it down faster. When the weight is travelling up, you are pulling it up faster. Even if you make very tiny movements, the weight will always bounce higher and higher.
If your spring was infinitely big, this weight would keep bouncing higher and higher with no limit!
The purpose of a damper is it always creates a force opposing the movement of the weight. This will set a maximum height to the bouncing. In systems like bridges this is a real problem. Bridges always sway a little bit, but a damper is put in place to make sure the swaying does not break the cables and supports holding the bridge up. If you want to see what would happen if a bridge did not have the correct damping, go to YouTube and search "Tacoma Narrows Bridge Collapse". (https://www.youtube.com/watch?v=esfpcnQW6qs)
