[Physics] Newton’s Third Law


Sorry if this question's been asked. I looked through some of the questions but didn't find a similar enough question.

My question on Newton's Third Law: It's my understanding that if you were in outer space and you threw a tennis ball then both you and the tennis ball would move but in opposite directions. Because you exert a force on the ball and it exerts an equal force on you. So how come when you push a wall on earth you get pushed back but not when you throw a ball. Can't you throw a ball with the same force you pushed the wall- if that's the case how come you don't move back? It's putting a force on you equal to the wall's force, right?

I do appreciate all the answers I've got but I guess I'm still confused. I understand that the ground pushes me in opposition to the wall's direction of force when the wall pushes my body, therefore my feet, on the ground away from the wall. But how come your arm and consequently your torso moves back when pushing a wall but not when throwing a ball.

Best Answer

When you throw a ball, you push it and it pushes you back. It just weighs slightly less than a wall (or the entire earth) so you don't need to push as much to move it.

You push a ball with enough force to move by acceleration $a$. This force is $F= m a$. This force is also exerted by the ground as a reaction to keep you in place. If you try to throw a ball on ice you will notice you will slide backwards or fall down.

Now if you try to "throw a wall" you need a force $F = m a$ that exceeds both the traction on your feet and what you can physically provide so nothing happens, or you slip and fall down.