If the ball hits the stick and bounces again, what’s going to occur to the stick? For those who mentioned the stick will recoil to the appropriate, you’re appropriate. 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, protecting the entire momentum of the ball-bat system fixed. We outline momentum because the product of an object’s mass and velocity.
For the reason that ball bounces again, the one method for momentum to be conserved is for the persist with recoil. (I do know, my setup for this thought experiment would make for a fairly lame spectator sport, however stick with me—it’ll assist us perceive what occurs on the candy spot).
Off-Middle 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 a substitute of the center. Like this:
The stick nonetheless recoils to the appropriate, 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 Angular momentum is rather a lot like plain outdated momentum besides that it offers with rotational movement as a substitute of linear movement.
Whereas linear momentum relies on the mass and velocity of the item, the angular momentum is the same as the product of the item’s angular velocity and its second of inertia. The second of inertia is just like the rotational mass—it relies on not solely the mass of the item however how that mass is distributed. So, after the stick recoils from the ball impression, it clearly has angular momentum, because it’s rotating.
However what about earlier than the collision? The stick is not rotating and would 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 would not rotate. (That is a type of moments when physics simply appears bizarre.) The angular momentum of the ball relies on its linear momentum and the place it hits the stick.
