Question

When a cracker explodes you see the pieces flying all around and not in one direction. What could be the reason? Before exploding the cracker was at rest.

Answer 1

because it bursts with a great pressure

Answer 2

My physics book says, "A firecracker sliding on ice has the same total momentum before and after it explodes." I understand this part. This is because of Newton's 3rd law, and no external forces. This is what I really don't get. "The same, however, is not true of a system's kinetic energy. Energetically, that firecracker is very different after it explodes; internal potential energy has become kinetic energy of fragments." It goes on to say, "Nevertheless, the centre-of-mass concept remains useful in categorizing the kinetic energy associated with a system of particles."

How is it that the kinetic energy increased but momentum stayed the same? My problem lies within the equation K=12mv2K12mv2 and p=mvpmv.

If kinetic energy increased doesn't that mean that the velocities increased as well? How else would KK become more positive? And since KK increased vv increased and thus p=mvpmv must increase?