Apply a force to the mass below the spring and see it move up and down. With no friction it keeps oscillating, but with some friction the oscillations are reduced (damped) and damped more with more friction. Friction is a force, proportional to the mass' velocity (change in position). You can select no, some or more friction.
When ERIC robot accelerates (by reversing direction), its circuit board, motors and battery pack oscillate. See how the oscillations decay with some / more control.
In both cases, the oscillations are reduced using the change in the quantity which oscillates: the mass's position or the angle of ERIC's board: ie using velocity feedback.
Press M to move the mass and F to change friction; Press R to reverse ERIC and C to change control.