Description
How does the whole system move when parts of it push on each other? In this AP Physics C: Mechanics video, we review the center of mass, take the derivative to get v_cm = Σp/M, and show that p_sys = M·v_cm. Because internal forces cancel in pairs, the center of mass keeps its velocity whenever the net external force is zero, even during an explosion or collision. Examples include two carts, a person walking on a boat, and a shell that splits in midair.
In this video:
0:00 Hook: a shell explodes at the top of its path
1:14 Center of mass review (from Unit 2)
2:18 Velocity of the center of mass
4:09 Forces and the center of mass
5:21 Example: velocity of the center of mass
7:33 Example: person on a boat
11:06 Example: a shell splits in midair
12:55 The big picture for 4.3
13:49 Preview: elastic and inelastic collisions
Download the guided notes and practice problems for this unit at houstonscience.com.
Part of the AP Physics C: Mechanics Unit 4 (Linear Momentum) series.