1. Chapter 13
Forces

2. 13-1 Nature of Forces
*Force:
push or pull
-gives nrg to an object

3. -Newton said an object in motion stays in motion unless acted upon by an outside force
(1st law of motion)
*Friction:
force that opposes the motion

4. -sliding friction
*when two solid surfaces slide over each other
-amount depends on two factors
1. Weight
2. Types of surfaces

5. -rolling friction
*object rolls over a surface
-oppose motion less than sliding
ex: wheels and ball bearings

6. -fluid friction *object moves through a fluid
-all liquids and gases are fluids
-usually opposes motion less than sliding friction
*Lubricants:
change sliding friction to fluid friction

7. -friction can be helpful
ex’s: ????

8. 13-2 Balanced and Unbalanced Forces
opp in direction and equal in size
-no change in motion
-keeps an object moving at constant velocity

9. *Unbalanced force:
not opp and equal
-always cause a change in motion

10. 3 laws of motion explain rest, constant motion, and accelerated motion
13-3 Force and Motion
3 laws of motion explain rest, constant motion, and accelerated motion
(Isaac Newton)

11. -1st Law of Motion *Inertia:
tendency of objects to remain in motion or stay at rest
-object at rest will remain at rest, and an object in motion will remain in motion, unless acted on by an unbalanced force(ex’s)

12. -2nd Law of Motion
Force = (mass)(acceleration)
N = (kg) (m/s/s)
-unbalanced force accel an object in the direction of that force
- 1N = 1kg X 1 m/s/s

13. -3Rd Law of Motion
*every action, there is an equal and opposite rxn
-all forces come in pairs
**Scooter Example**

14. 13-4 Gravity

15. -Free fall
-All objects accel at the same rate, regardless of their mass
*Gravity:
attractive force b/all objects in the universe

16. -Free fall
~near the surface of earth, accel due to gravity 9.8m/s/s
-Any falling object meets air resistance
*Terminal vel:
no longer accel (120mph)

17. -Projectile Motion
*any object thrown in the air
~is always a curve
-Once you release a ball the only force acting on it is gravity

18. Orbital Motion
*object that orbits another object
~it is a result of the object’s forward inertia and the downward pull of gravity on the object

19. -Newton’s Law of Universal Gravitation
*all objects in the universe attract each other by the force of gravity
-The size of the force depends on: 1)mass 2)distance b/them

20. 13-5 Weight and Mass -Weight:
measure of the force of gravity on an object
~units: newton (N)
~w = m x g
-Mass:
amount of matter
~mass is constant