In this chapter we are going to combine what we've done in Chapter 2 and Chapter 3, and bring us to the law of conservation of momentum, which is the first real "rule" of nature that we are going to s...In this chapter we are going to combine what we've done in Chapter 2 and Chapter 3, and bring us to the law of conservation of momentum, which is the first real "rule" of nature that we are going to study in this book. The first puck has a momentum of 5 kg m/s, the second has 7 kg m/s - but it's moving the opposite direction, so the initial momentum in the x-direction is p_{i,x}=5 \text{ kg m/s} - 7 \text{ kg m/s} = -2 \text{ kg m/s}.
