Newton's 1st Law Question

Question

So for this one, I place a ball on a flat surface (such as a book). What happens when: I suddenly move the book forward? I suddenly move the book backward? I slowly move the book forward with a constant velocity, then suddenly stop? Did my observations match your expectations from Newton’s 1st law? Why or why not?

Answer 1

In each case, the ball starts off standing still without rolling. The forces on it are its weight pulling it down, an equal and opposite force from the book that supports the ball, and friction from the book pulling the bottom of the ball in the direction the book is moving. The horizontal force has the combined effect of accelerating the center of the ball in the direction of the force and accelerating rotation about the center of the ball because the ball is not being pulled from its center. You will observe the ball begin to move horizontally but roll in toward the opposite direction. If you stop moving the book, the new initial conditions include both motions on the ball, Friction from the book will slow it down and gradually stp the rolling. The ball will come to rest in a different place on the book

Answer 2

The best way to answer this question is to try it. It's a simple experiment that anyone can try. Do it. If you don't have a ball, try an apple, orange, or anything sort of round.

You will see that objects that are still, tend to stay still. It's like they WANT to stay still. And objects that are moving, tend to stay moving. It's like the WANT to stay moving. This is Newton's 1st Law.