"The most beautiful thing we can experience is the mysterious... It is the source of all true art and 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.