1. The problem statement, all variables and given/known data A ball hits a wall with momentum p1. The book says the momentum "returned" by the wall equals -2p1 .. i.e. it doubles. What does that mean? Here's why I ask: If I throw a ball against a wall and it comes back and I catch it, I KNOW the momentum has not doubled just from the feel of the catch in my glove. If I were to hit a golf ball against a wall, I KNOW that the ball does not come back at twice the speed. Where p = mv going to the wall, it sure doesn't come back at twice the velocity or m(2v). The closest I can come to understanding this is ... at the wall, when the ball hits, the wall moves in the direction the ball is coming .. that is one of the mv which the ball puts into the wall. THEN, the wall returns in the - direction another mv ( elastic ), and that is the 2nd mv that makes up the -2mv. But EACH mv is separate, and only jargon connects them into 2mv ... not reality. And it is the 2nd mv returned to the ball by the wall that gives the ball an Impulse Ft = mv ........... NOT 2mv. The first mv was just stored in the wall .. and returned in an elastic response. Is that right ? And if that is right, then should I view the wall as an elastic spring which generates the inpulse AFTER it is compressed? The first mv compresses the spring. The second mv returns the "impulse" to the ball?