1. Chapter 2 Sec. 2 Friction and Gravity

2. Friction Forces Friction is caused by the touching of two objects
Will cause an object to slow down and finally stop
The rougher the surface the higher the friction.

3. The Good Friction
Friction allows us to walk – friction between the ground and our shoes
Allows car to travel and stop – friction between tires and the road

4. Types of Friction
Static Friction – Friction between non-moving objects.
Sliding Friction – Friction between objects that slide past each other.
Rolling Friction – Friction between objects that roll.

5. Gravity All objects exert a gravitational force.
The amount depends on the amount of matter.
Gravity keeps us on the ground because the Earth has a lot of matter.
                                                       

6. What Determines Gravity
Gravity = Mass(m1) x Mass(m2)
distance (d2)
If the objects are massive then gravity is larger.
If the objects are far apart then the gravity is less.

7. Gravity on Earth All objects fall to Earth at the same rate.
The acceleration due to gravity is 9.8 m/s2.
For calculation purposes we will say the acceleration is 10m/s2

8. Gravity on Earth Cont’d
For every second an object falls to Earth, its velocity increases by 10m/s.
If a rock falls for 8 seconds, How fast will it be traveling?

9. Weight vs. Mass Weight measures how gravity affects mass.
Mass is the amount of matter in the object.
Your scale tells you how earth’s gravity is affecting you.

10. Air Resistance
Air resistance opposes the motion of objects through the air.
Everything on earth would fall at the exact same speed if it wasn’t for air resistance.
Air resistance depends on the speed, size, and shape of an object.