Lesson Objectives What is friction What causes friction

Lesson Objectives • What is friction? What causes friction? • Friendly Friction, Unfriendly Friction • Ways to reduce Friction

Friction is a f____ that slows down or stops the movement of 1 surface against another. What is friction caused by? Caused by the microscopic lumps on one object catching and sticking to the l_____ on the other object. Rough surface, greater resistance Smooth surface, l___ resistance

Views through a microscope

Friendly Friction We need friction to do many things. Walking requires friction.

Friendly Friction Holding object requires friction. Wet hands and wet soap provide no grip.

Friendly Friction Stopping a bicycle requires friction. When brake pads press against the rim of wheel, the bike can stop.

Unfriendly Friction causes wear and tear of our shoes Friction causes unwanted heat too!

Unfriendly Friction For machines that have many parts rubbing together, heat, noise (sometimes), wear and tear results.

Ways to Reduce Unfriendly Friction • To allow machinery to move more freely, . lubricant (such as oil and grease) is used. • Polish the surface so that it is smoother • The oil separates the 2 surfaces so that they do not catch each other.

Ways to Reduce Unfriendly Friction Ball Bearings are used to reduce sliding friction. Rolling friction is less than sliding friction.

Reduce Unfriendly Friction • Separate the 2 surfaces with air e. g. hovercraft

Ways to Reduce Unfriendly Friction Streamline cars, planes, water craft to reduce air friction.

• air f______ slows down a parachute so that a parachutist can land safely • knots in string and threads in your clothes are held together by f_______

Friction can be useful • Cyclists depend on the friction at brake pads and wheels to slow down