If the ball hits the stick and bounces again, what is going to occur to the stick? For those who mentioned the stick will recoil to the best, you’re right. We are able to consider this as a collision. When two objects collide, they exert forces on one another. And per Newton, the forces are equal and reverse, holding the whole momentum of the ball-bat system fixed. We outline momentum because the product of an object’s mass and velocity.
Because the ball bounces again, the one means for momentum to be conserved is for the persist with recoil. (I do know, my setup for this thought experiment would make for a reasonably lame spectator sport, however stick with me—it’ll assist us perceive what occurs on the candy spot).
Off-Heart Collision
OK, go fetch the stick and convey it again to the beginning place. The ball is once more launched towards the stick. Nevertheless, this time, it is aimed on the finish as an alternative of the center. Like this:
The stick nonetheless recoils to the best, however now it additionally rotates about its middle, proper? Why does this occur? Properly, momentum continues to be conserved, however now there’s one other conserved amount—angular momentum. Angular momentum is loads like plain outdated momentum besides that it offers with rotational movement as an alternative of linear movement.
Whereas linear momentum is determined by the mass and velocity of the article, the angular momentum is the same as the product of the article’s angular velocity and its second of inertia. The second of inertia is just like the rotational mass—it is determined by not solely the mass of the article however how that mass is distributed. So, after the stick recoils from the ball influence, it clearly has angular momentum, because it’s rotating.
However what about earlier than the collision? The stick is not rotating and does not have angular momentum, so for angular momentum to be conserved then the ball should have angular momentum. Sure, a mass can have angular momentum even when it does not rotate. (That is a kind of moments when physics simply appears bizarre.) The angular momentum of the ball is determined by its linear momentum and the place it hits the stick.