| 8.8.1: A 12 kg box slides down a rough ramp as shown in the animation. | 8.8.2: A metal bar is stretched by a force as shown in the animation. |
| 8.8.ap 1: A 1.5 kg block receives a push and in the process pushes against a 4.5 kg block as shown in animation 1. Conversely, in animation 2, the same 4.5 kg block receives the same push, now from the opposite direction and in the process pushes against the 1.5 kg block. |