What happens to the stick if the ball hits the stick and bounces back? If you say the stick will recoil to the right, that’s right. We can think of it as a collision. When two objects collide, they exert force on each other. And according to Newton, the forces are equal and opposite, keeping the total momentum of the ball bat system constant. We define momentum as the product of the mass and velocity of an object.
Since the ball bounces, the only way to maintain momentum is to recoil the stick. (I know that this set of my thought experiment will create a very lame audience sport, but living with me – this will help us understand what will happen in the best location).
Deviating from the center
OK, go and pick up the stick and take it back to the starting position. The ball fired at the stick again. However, this time it is for the end rather than the middle. Like this:
The stick is still sitting to the right behind, but now Rotate About its center, right? Why does this happen? Well, momentum is still conservative, but now there is another conservative number – angular momentum. Angular momentum is much like ordinary old momentum, except that it handles rotational motion rather than linear motion.
Although linear momentum depends on the mass and velocity of the object, angular momentum is equal to the product of the object’s angular velocity and its moment of inertia. Moment of inertia is like a rotational mass, which depends not only on the mass of an object, but also on how that mass is distributed. So after the ball hits, after the stick recoils, it obviously has angular momentum because it is spinning.
But what before the collision? The stick does not rotate and has no angular momentum, so keep the angular momentum, and then ball Must have angular momentum. Yes, the mass can have angular momentum even if the mass does not rotate. (This is one of the seemingly strange moments in physics.) The angular momentum of a ball depends on its linear momentum and It hit the stick.
