1. Bell Ringer 1-27-10 See if you can answer these from memory:
What is a force?
What unit measures force?
A ________ is a combination of all the forces acting on an object.
List the two types of forces and the key words we use to remember them.

2. Chapter 10 section 2 friction and Gravity

3. Friction Foldable
Once your paper is folded, label the four sections with the four types of friction:
Static friction
Sliding friction
Fluid friction
Rolling friction
p. 342

4. Types of friction
Static friction – friction that acts on objects that are not moving Ex. Pushing on a heavy refrigerator/ driving off with a book on top of the car
Sliding friction – friction that occurs when 2 solid surfaces slide over each other Ex. Bike brakes/ ballet dancers

5. Types of Friction (cont’d)
Rolling friction- occurs when an object rolls across a surface (ex: skateboard on road)
Fluid friction – occurs when a solid object moves through a fluid (ex: surfboard on water)

6. Who is this?
Sir Issac Newton

7. Gravity Gravity- a force that pulls objects toward each other
Ex: Earth pulling us toward it
Law of Universal Gravitation- the law that states that the force of gravity acts between all objects in the universe
Why don’t you feel the gravity between other objects and you?

8. Gravity Two factors affect Gravity: 1. Mass 2. Distance
amount of matter in an object
Not affected by gravity
Greater the mass, greater the gravity
Ex: sun and planets
2. Distance
Increase distance, decrease gravity

9. Weight
Weight- the force of gravity on an object or person

10. Air Resistance
Air Resistance- an upward force exerted on falling objects
It’s not the same for all objects.
The greater the surface area, the greater the air resistance.

11. Terminal Velocity
Terminal Velocity- the greatest velocity a falling object reaches
Exists when the force of air resistance equals the weight of the object/or the force of gravity pulling down on the object
Air Resistance = Weight or Gravity

12. Projectile Projectile- an object that is thrown
Will an object that is thrown horizontally land on the ground at the same time as an object that is dropped?

13. Exit Quiz 1-26-10 What is a force?
The combination of all the forces acting on an object is called ______.
If two forces are balanced, is there a net force?
The SI unit for force is the ________.
Tell me one of the four types of friction and give an example.