1. bellringer In your composition books
Draw a free-body diagram of you sitting on a chair (make-sure to include all the forces)
What is a normal force? Define and draw a picture

2. 5.2 friction
Davis

3. What is friction A force that resists motion.
Found everywhere in our world
Can act when an object is moving or when it is at rest.
Depends on both the surfaces that are in contact

4. Identifying friction of forces
Draw force of friction with a force vector
Friction is measured in Newtons
The force of friction acting on a surface ALWAYS points OPPOSITE the direction of the motion of that surface

5. Types of friction
Sliding friction: friction forces that resist the motion of an object moving across a surface

6. Types of friction cont.
Static friction: the friction force that resist the motion between two surfaces that are not moving
As you increase the strength of your push, the static friction also increase (eventually your force becomes strong enough to overcome static friction and the box starts moving)
Static friction is almost ALWAYS GREATER than sliding friction

7. Different amounts of friction
The amount of friction generated when a piece of paper is slide across a table vs. adding a brick to the piece of paper than sliding it across the table is different.
The greater the force squeezing two surfaces together, the greater the friction force

8. Decreasing friction Lubricants
Oil: can be used between 2 sliding surfaces to keep them from touching each other.
Example: you add oil to a car’s engine so that the moving parts slide or turn with less friction
Water
Ball bearings
Separating the 2 surfaces with a cushion of air
Example: metrorail (the train is separated from the train tracks maglev which allows the train to float on the tracks when it is moving this allows the ride t be smoother and faster)

9. Increasing friction
Brakes on a bicycle create friction between the brake pads and the rim of the wheel making the bicycle slow down or stop
Tires of a car or any vehicle
Cleated shoes are designed to increase the friction between your foot and the ground

10. Friction and energy Friction changes energy of motion into heat energy
(rubbing hands together causes your hands to get warm)
Friction is ALWAYS present in any machine with MOVING PARTS
(example: sewing machine)
Another way friction changes energy is by wearing away moving parts
(example: water flowing over stones) each time 2 moving surfaces touch each other , tiny bits of materials are broken off by friction- this uses energy and causes the rocks to be round and smooth