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Friction and Gravity

Friction

• The force one object exerts on another when they move past each other

– Strength depends on:

• Types of surfaces involved

• How close the surfaces are to each other

• Example

Type of surface involved

• Imagine skiing or snowmobiling on bare ground…what would happen?

The type of surface determines friction

• Snow grips the skis less…

– Therefore there is less friction

• Dirt grips the skis more…

– Therefore there is more friction

– So much that it may cause

How hard surfaces push against each other

• The harder two surfaces push against eachother…the more friction is produced

– Atoms rubbing against each other

– Example

• Fish tank demo/Class demo

– Mass can increase friction

Useful Friction

• List some examples of how friction helps/doesn’t help you.

• You will be responsible for this on a test/quiz

Controlling Friction

• Sliding Friction-When solid surfaces slide over one another

• Rolling Friction-When an object rolls along a surface

• Fluid Friction-When an object moves through a liquid or gas

Sliding Friction

Rolling Friction

Fluid Friction

• Would skiing be an example of fluid friction, rolling friction or sliding friction?

• Would running be an example of fluid friction, rolling friction or sliding friction?

• Would dropping a rock in water be an example of fluid friction, rolling friction or sliding fricition?

Gravity

• Is a forces that pulls objects towards each other.

Free Fall

• When the only force acting on an object is gravity…an object is in free fall.

Projectile Motion

• Projectile-an object is launched horizontally

– Example

Air Resistance

• Fluid friction that deals with traveling though air

• Hand Planes

Weight vs. Mass

• Mass-How much matter is in an object

• Weight-The force of gravity pulling on an object

– Varies

– Weight =Mass x Acceleration due to gravity

Universal Gravitation

• States that the force of gravity acts on all objects in the universe

• You have gravity

• Strength depends on distance and mass

– Large close object=more gravity

– Small distant object=less gravity