1. Monday, October 22, 2012

3. Today's agenda:
1. Warm-up
2. Pass back a couple papers and review them.
3. Lecture on the concept of friction.
Remember upcoming events:
- notebook & portfolio check
- test over Chapters 3, 4, 5

4. Chapter 4 concepts

5. Chapter 4 concepts

6. Chapter 5 concepts

7. Chapter 5 concepts

8. Answers to Ch. 5 Questions (#7-11, pg. 71)
You needed to provide sketches, also.
7. 20,000-N
8. Surface irregularities; opposes motion.
N; zero net force; zero acceleration.
10. Force- a push or a pull; pressure- force/area.
11. Standing up produces more pressure.

9. Friction
A force between all materials with surfaces in contact with each other.
- Depends on the kinds of material in contact and how much the surfaces are pressed together.
- Always acts in the opposite direction of relative motion.

10. Friction (continued)
Fluids - anything that flows (liquids, gases). Fluid friction occurs when objects move through a fluid.
- Air resistance is the friction acting on something moving through air.
- Free body diagram (FBD) -
shows all forces acting
on an object. See pg 64

11. Friction (continued) Static Friction: friction between two stationary
Sliding Friction: friction between two objects that are sliding against one another
Rolling Friction: friction between two surfaces when one is rolling
Static Friction > Sliding Friction > Rolling Friction

12. Friction (continued)
Push harder until surfaces “break” apart. Static Friction was overcome.
Fpush > Force of Static Friction
Once the box begins moving, push (“back off some”) such that the box moves at a constant speed
Fpush= Force of Sliding Friction

13. Friction (continued) Fluid : anything that flows (gases and liquids)
AIR FRICTION (Air Resistance)
Depends on three things:
1. Surface Area
2. Mass
3. Speed