If we jump barefooted on a hard surface, our legs get injured. But they r not injured if we jump on a soft surface like sand or pillow. Plz explain?

Asked by varonika | 5th Aug, 2010, 12:00: AM

Expert Answer:

When you jump on any surface, then there is change of momentum when you land on the surface from above. Your momentum goes from a certain value to almost zero. This change in momentum is due to the force acting on your leg while it makes contact with the surface. Now, for the case of pillow, since it is soft, so your legs push it downwards for 1 or 2 seconds then your legs stop. So, in this case the change in momentum takes place in 2 or 3 seconds, whereas in case of a hard surface, the change in momentum comes almost instantaneously. So in the case of a pillow the impulse imparted is less as time taken to change the momentum is more, and in case of the hard surface almost in an instant impulse is imparted. So the value of impulse in the case of a hard surface is much much greater than the case of a sorf surface such as pillow or sand etc. That is why your legs cant stand the impulse in case of a hard surface and gets injured whereas they comfortably jump over a soft surface.

Answered by  | 5th Aug, 2010, 10:34: PM

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