1. Free Body diagrams
Free body diagrams show all the forces that are present on an object.
Size of force arrows to represent magnitude of force
Unbalanced forces result in acceleration
Equal and opposite forces = no acceleration

2. Free Body Diagrams 1. A 60 kg girl stands at rest on the floor.
2. The 60 kg girl sits at rest on a playground swing.
3. A 1 kg lump of clay is stuck to a vertical wall.
4. A 500 kg car is traveling at a constant velocity on a flat road.

3. 5. The car in #4 is speeding up from 50 to 60 mph.
6. The same car is skidding to a stop.
7. A boy uses a rope to pull a 10 kg box across the floor at constant velocity.
8. In #7, the boy’s 20 kg sister is sitting on the box.

4. 9. A man pushes a 15 kg lawn mower at constant velocity.
10. A 1.5 kg book is sliding to a stop across a table.
11. The 1.5 kg book sits at rest on the 30º ramp.
12. A 70 kg skier accelerates down a 30º slope.

5. 13. The system shown below is at rest due to friction from the table.
14. One mass goes up and one goes down (no friction).
M=5kg
M=5kg
m=2kg