If the ball hits the stick and bounces, what will happen to the stick? If you said the stick fell to the right, you are right. We can consider this as a collision. When two objects collide, they exert forces one on the other. And by Newton, the forces are equal and opposed, keeping the total amount of movement of the constant ball ball system. We define the impulse as the product of the mass and the speed of an object.
Since the ball bounces, the only way for the momentum to be preserved is that the stick fell. (I know, my configuration for this thought experience would make a fairly lame spectator sport, but will remain with me – it will help us understand what is going on at Sweet Spot).
Outside collision
Ok, go get the stick and bring it back to the starting position. The ball is launched again towards the stick. However, this time, it is addressed at the end instead of the middle. Like that:
The stick always decreases to the right, but now it's also turn About his center, right? Why does it happen? Well, the momentum is still preserved, but now there is another quantity preserved – an angular momentum. The angular momentum is very similar to an old impulse, except that it deals with the rotation movement instead of a linear movement.
While the linear moment depends on the mass and the speed of the object, the angular moment is equal to the product of the angular speed of the object and its moment of inertia. The moment of inertia is like the mass of rotation – it depends not only on the mass of the object, but on the way in which this mass is distributed. Thus, after the stick fell back from the impact of the ball, it clearly has an angular moment because it turns.
But what about the collision? The stick does not turn and has no angular moment, so for the angular moment to be kept so the ball Must have an angular moment. Yes, a mass can have a angular moment even if it does not turn. (This is one of those moments when physics seems bizarre.) The angular moment of the ball depends on its linear momentum And where he strikes the stick.
