1. Force Diagrams

2. Some commonly used conventions: Smooth, as in “A smooth surface” or “A smooth pulley” implies that friction is ignored. Rough, as in “A rough surface” or “A rough pulley” implies that friction is taken into account. Unless stated otherwise, objects are modelled as particles. Unless stated otherwise, all units are SI units which are: Force: Newtons (N) Distance: Metres (m) Mass: Kilogrammes (kg)Time: Seconds (s)

3. Arrow conventions: Forces: Velocity: Acceleration:

4. Apple falling in space (air resistance ignored). W = mg 9.81 ms -2

5. Apple hanging from a tree. W = mg T

6. Book resting on table. W = mg N

7. Book being pulled across smooth surface. W = mg N P

8. Book being pulled across rough surface. W = mg N PFrFr

9. Book sliding down smooth surface. W = mg N

10. Book sliding down rough surface. W = mg N FrFr

11. W1W1 W2W2 T T Two masses, joined by a light string, passing over a smooth pulley.

12. Important! If a force is resolved into two perpendicular components which are equivalent to the original force, never show the original force and the resolved components on the same diagram.