gravitational force and irreversibility If we place a ball at a certain height it falls and the process is irreversible. Is there any entropy change associated with the falling of ball? If so why?
 A: Actually, the process you described is not irreversible.  What has happened is that potential energy has been converted to kinetic energy.  It is possible to reverse the process by using a roller coaster kind of arrangement where the ball is redirected to go up a hill.  In the end, its kinetic energy is converted back into potential energy.  There is no irreversible conversion of mechanical energy to either heat or internal energy.  The change in entropy is zero.
Now, if we let the ball bounce, and continue bouncing, its height of bounce will decay, and it will eventually stop.  In that case, there is an irreversible conversion of mechanical energy to heat or internal energy, and the temperature of something (or some things) will increase (ball, floor, air, etc.).  In that case, there will be an increase in the entropy of the universe (whatever eventually increases in internal energy). 
A: 
If we place a ball at a certain height it falls and the process is irreversible.

The process you described is irreversible. A object, falling towards a source of gravity, does not experience any force and by this does not accelerate. That seems to be paradoxical. To see that this is right you have to do the journey together with the ball. If there is no atmospheric friction you will be weightless and by this you could not decide between still standing and a force free movement. That is what Einstein meant than he spoke about curvature of space. No forces, only geodesic paths. As long as you speed up (in relation too the earth) your system is in balance, no force is acting on it.
But you know that you in danger and what will happens.Touching the ground, the ball gets accelerated (with a minus sign) and if the ball has the property of elasticity it will came to rest and the get accelerated again. Are you familiar with the emission of photons during acceleration? Every acceleration is related by the emission of photons. So as long as you in free fall, nothing happens. During the braking and acceleration the body emits photons. This is an irreveresible loss of energy and a change in entropy.
This phenomenon is ignored doe to the small size in relation to the energy loss by the elastic deformations. BTW, heat produced by this elastic deformations is also an ireversible process.
