1. Friction, Gravity, and Elastic Forces
Chapter 10 Section 2
Friction, Gravity, and Elastic Forces

2. Friction
Friction is a force that two surfaces exert on each other when they rub against each other.
Friction is caused when the irregularities of one surface come into contact with those of another surface.
The strength of the force of friction depends on the types of surfaces involved and how hard the surface push together.

3. Types of Friction
1. Static Friction: Is a friction that acts on objects that are not moving.
2. Sliding Friction: Occurs when two solid surfaces slide over each other.
3. Rolling Friction: Occurs When an object rolls over a surface.
4. Fluid Friction: Occurs when a solid object moves through a fluid. (fluids in science are all the liquids and gases)

4. Gravity Gravity is a force that pulls objects toward each other.
Newton was the first scientist that talked about Gravity
Law of Universal Gravitation states that the force of gravity acts between all objects in the universe.
Gravity depends on Mass and Distance; The force of gravity between objects increases with greater mass and decreases with greater distance.

5. Weight is a measure of gravitational pull.
The measure of amount of matter in an object is its mass. The SI unit of mass is gram (g) or kilogram (Kg).
Weight is a measure of gravitational pull.
Weight=Mass X Acceleration due to gravity
Acceleration due to gravity is 9.8m/s/s
Newton is unit for Weight. (N)

6. Gravity and Motion
Free fall: An object is in free fall when the only force acting on the object is gravity.
In Free Fall, the force of gravity alone causes an object to accelerate in the downward direction.
The acceleration due to gravity is 9.8m/s/s.

7. Air Resistance is an upward force exerted on falling objects.
Air Resistance is a type of fluid friction acting on all falling objects.
Objects with greater surface area experience more air resistance as they fall.

8. When objects are thrown horizontally they travel in a projectile motion.
Matter is considered Elastic if it returns to its original shape after it is squeezed or stretched.
Compression is an elastic force that squeezes or pushes matter together.
Tension is an elastic force that stretches or pulls matter.