1. Friction

2. Friction Definition
Friction occurs when 2 objects are in contact with each other. The objects apply or exert a force on one another during this time.
Friction acts in the opposite direction of motion – so it is the force that resists movement!
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3. Factors that Affect Friction
How hard the surfaces push against each other – the more force, the higher the friction
The type of surfaces involved – the smoother the surface, the lower the friction

4. Friction and Smooth Surfaces
Even apparently smooth surfaces actually have microscopic irregularities and bumps. When these come in contact with another surface friction occurs.

5. Direction of Friction
Friction acts in the opposite direction of motion, so if the object moves towards the right the frictional force will be towards the left.

6. Static Friction Definition:
The friction that occurs when objects are not moving. It is the friction that keeps objects in place.
Example:
A box sitting on the ground, your books sitting on a table, your backside against the chair.

7. How to “Overcome” Static Friction
The force needed to start an object moving must be greater than the static friction.
Reason why a greater force is needed to start an object moving than to continue it moving
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8. Sliding Friction Definition:
The friction that occurs when 2 solid objects move against each other (or 1 object moves over another)
Example:
Bicycle brakes, skinning your knee, walking, writing

9. Usefulness of Sliding Friction
It can keep you from slipping, sliding and falling (example: sand on an icy road)!

10. Rolling Friction Definition:
The friction that occurs when an object rolls across a surface.
Easier to overcome than sliding friction.
Example:
Anything with wheels (cars, skateboards) or a ball rolling.

11. Rolling Friction and Engineers
Engineers use ball bearings to reduce friction – the ball bearings roll between moving parts.
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12. Fluid Friction Definition:
The friction that occurs when a solid objects moves through a fluid. A fluid is a gas or liquid – they flow easily!
Easier to overcome than sliding friction.
Example:
Anything moving through the air or water: riding a bike, surfing, swimming, sky diving

13. Usefulness of Fluid Friction
Parts of machines move more easily when they are oiled.
Fluid friction is what slows down a skydiver when the parachute is opened.