Today is the finale of the soccer world championship and the last opportunity ta ask my reader the following question:

When a player receives a ball on his head, the ball is compressed for a very short moment before it is bounced back. Have a guess, what is the maximal deformation of the ball (in cm)?

Here are some measures about the soccer ball according to the rules of the FIFA: it is of spherical shape, made with leather or similar material and has, at the beginning of the match, a circonference between 68 and 70 cm, a weight between 410 and 450 g and a pressure between 1,6 and 2,1 atm (1600 - 2100 g/cm²).