Question

Why does a fielder in the game of cricket pull his hands back when he catches a ball?

Answer 1

Newton’s second law relates the rate of change of momentum with respect to time with the force exerted on an object. To avoid injury, the player tries to decrease the force exerted by the ball on their hands.

Formula used:
$\Rightarrow F = \dfrac{{\Delta P}}{{\Delta t}}$ where $\Delta P$ is the change in momentum of the ball and $\Delta t$ is the time period in which the change of momentum occurs.

Complete step by step solution:
Newton’s second law tells that the force acting on a body is equal to the rate of change of momentum of the body i.e. $F = \dfrac{{\Delta P}}{{\Delta t}}$. When a fielder is catching a ball, the ball is in the process of transferring its momentum to the player’s hands. To avoid injury, the fielder must make sure that the ball exerts the least amount of force on their hands.
Since the momentum transfer by the ball cannot be controlled by the player, they pull their hands back and increase the time period in which the ball transfers its momentum to the player’s hands i.e. increase $\Delta t$. Since $\Delta t$ increases, the force exerted on the player's hands will decrease and they can safely catch the ball without causing any injuries. By increasing the time period of the catch, the players can also avoid the ball from bouncing off their hands and missing the catch.

Note:
Here we have assumed that the ball is incompressible and transfers its momentum completely to the player’s hands. However, in reality, softer balls like tennis balls can get compressed and lose their momentum and as a result, it’s easier to catch such balls at high speeds without causing any injuries.