1. Friction

2. What Is Friction
Friction is a force that opposes motion between two surfaces that are touching.

3. The Source of Friction
Occurs because the surface of any object is rough.
Objects that feel or look smooth are actually covered with microscopic hills and valleys.
The amount of friction between two surfaces depends on many factors, including the roughness of the surfaces and the force pushing the surfaces together.

4. What Creates More Friction?
Rougher surfaces create more friction.
ex. Pavement vs. Grass vs. Ice
Greater forces create more friction.
* Depends on amount of force pushing
the two surface together.
ex. Science book on a table vs. a
notebook on a table

6. Types of Friction
Sliding Friction
Rolling Friction
Fluid Friction
Static Friction

7. Sliding Friction
Sliding friction is very effective at opposing the movement of objects and is the force that causes objects to stop moving.
Examples: pushing pencil across table, moving furniture, sledding, apply brakes to bike or a car, write with a piece of chalk.

8. Rolling Friction
The force of rolling friction is smaller and easier to overcome than sliding friction.
Rolling friction is an important part of almost all means of transportation.
Examples – bikes, cars, trains, skateboards

10. Fluid Friction Fluid Friction is less than sliding frictions.
The term fluid includes liquids, such as water and milk, and gases, such as air and helium.
Fluid friction opposes the motion of objects traveling through a fluid.
Fluid friction between air and a fast moving car is the largest force opposing the motion of the car.

11. Static Friction
When a forces is applied to an object but does not cause the object to move, static friction occurs.
The object does not move because the force of static friction balances the force applied.
Static friction disappears as soon as an object starts moving, and then another type of friction immediately occurs.

13. How is Friction Harmful
Friction by wind and water can cause erosion.
Friction between problems in the moving parts of an engine…rub together and increase temperature.
Helpful
Need friction between paper and pencil to write.
Need friction to walk, without it you would just slip and fall.

14. Ways to increase and decrease friction
Increase Friction
Make surfaces rougher.
Increase the force pushing the surfaces together.
Decrease Friction
Use lubricants (substances that are applied to surfaces to reduce friction between them.)
Switch from sliding friction to rolling friction.