An object is suspended from a vertical spring as shown in the figure below.
The object is displaced vertically and then released so that it oscillates, undergoing simple harmonic motion. The graph shows the variation with displacement 
of the energy 
of the oscillations.
State the cause of damping.
A light card is attached to the object. The object is displaced with the same initial amplitude and then released. During each complete oscillation the total energy of the system decreases by 
of the total energy at the start of that oscillation. State, with a reason, the type of damping that the card introduces into the system.
