Yesterday I saw that a ping pong ball bounced nicely on a hard surface but poorly on a mattress.On the contrary ,I saw that other things (a pen for example) bounced poorly on a hard surface but nicely on a mattress

Please I want to know the reason behind the motion and more importantly why the difference is there


I found that certain materials rapidly lose their Kinetic energy on striking hard surfaces but a mattress manages to store the kinetic energy of the object as elastic potential energy and returns it in accord with its elasticity.

What I find intriguing now is the properties of the material which contribute to loss of KE. Any help is highly appreciated.

NOTE: I ensured that the pen hit the surface with minimum area in contact (the side from which the nib comes out) and the nib was removed.

       The pen material didn't look like it could be easily be deformed.

1 Answer 1


See here the shape of the object matters. As the ping pong ball has following two reasons -

  1. The spherical shape provides it a perfect impact while returning through the hard surface. While the mattress has the resistance towards the motion of the ball and lets it loose its impact very quickly.
  2. The pen has the unfurnished (as compared to the ball) which effects its bounce on the hard surface and even lets it loose the energy within the short time which is the reason it doesn't bounce or return back. While mattress provides a good amount of unbalanced forces on the pen.

$$Impact={1\over A}$$ (here $A$ is the area of the object)

  • 2
    $\begingroup$ I didn't understand why the shape of the pen had such an effect $\endgroup$
    – mnase
    Feb 19, 2017 at 12:50
  • $\begingroup$ Easy if you drop a pen then it generally falls down with the cylindrical or the curved part. $\endgroup$ Feb 19, 2017 at 13:19

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