Friction A World Without Friction Friction A force

Friction

A World Without Friction…

Friction • A force that resists motion • Occurs due to the attraction between particles

Two Types of Friction Kinetic Friction • Occurs when the object is in motion • Resists movement

Two Types of Friction Static Friction • Occurs when the object is stationary • Resists being put in motion

How do we measure friction? • • Weigh an object with a force scale Pull an object with a force scale Divide the two values We call the result the coefficient of friction

Coefficient of Friction ( ) • Ratio of the magnitude of the frictional force to the normal force (how much force is pushing up from the surface) • Coefficients of friction can be found in the text – Page • Depends on the two surfaces in contact

• http: //www. engineeringtoolbox. com/frictioncoefficients-d_778. html • Pick one!

The Math - Coefficient of Friction (no units) Ffr – Force of Friction (N) FN – Normal Force (N)

Example # 1 The coefficient of static friction between ___ and ___ is _____. Find the minimum force required to start an 8. 0 kg mass moving.

Example # 2 • An 8. 0 kg teflon pot is on a steel table. If it takes 9. 4 N of force to keep the pot moving at a constant speed. What is the coefficient of friction between the pot and table?

Controlling Friction • How can we reduce friction? • Why do we need to reduce friction?

Controlling Friction What is used to increase friction? Why do we need to increase friction?

Industrial Applications • Inertial Friction Welding ▫ Video • Creating a Friction Fire http: //www. youtube. com/watch? v=VOmw. Lxg. I 06 c