"the most beautiful thing we can experience is the mysterious... it is the source of all true...

• "The most beautiful thingwe can experience is the mysterious... It is the source of all true artand all science."

• - Einstein

What is a force?

• any straight-line push or pull

Units of force

Newton (metric) (weight of 1 apple)

Friction

A force that opposes motion between two surfaces that are in

contact

The Source of Friction

• When surfaces are rough

• Even if surfaces are covered in microscopic hills.

Two types of Friction

• Kinetic: Kinetic means “moving”

Sliding

Rolling

Kinetic Friction

• Rolling Friction: slows down the motion of an object rolling on a surface". Rolling friction slows down the motion of a tire rolling along the pavement.

Kinetic Friction

• Sliding Friction: "the force that occurs when two objects slide against each other". An example of sliding friction is striking a match against a rough surface.

Kinetic Friction

• The force of sliding friction is greater than the force of rolling friction.

Static Friction

• the force that keeps an object that is not moving in its place". A vase on top of a table is an example of static friction.

Ways to reduce Friction

• Lubricants: motor oil, wax and grease.

Ways to increase Friction

• Make examples rougher

• Examples: sand scattered on icy roads.