Friction Every day you see moving objects come

Friction • Every day you see moving objects come to a stop. • The force that brings nearly everything to a stop is friction • FRICTION is the force that acts to resist movement between two touching surfaces.

Friction, continued • Objects cannot move with a constant speed unless a net force is applied because friction is always acting to slow down the motion • If friction could be removed, an object in motion would continue to move in a straight line with constant speed.

Friction, continued • In the vacuum of outer space, there is no friction to slow motion • Therefore objects continue to move indefinitely (like the moon around the earth)

Opposing Sliding • If two objects are in contact, frictional forces always try to prevent one object from sliding on the other object. • If you rub your hand against a tabletop, you can feel the friction push against the motion of your hand. • Friction will always slow an object down.

Static Friction • STATIC FRICTION prevents an object from moving when a force is applied • It is caused by the attraction between atoms on the 2 touching surfaces which cause the surfaces to stick together

Static Friction, continued • To move the object, you have to exert a force large enough to break the bonds holding two surfaces together. • Generally, the rougher the surface or the heavier the object, the more static friction.

Sliding Friction • SLIDING FRICTION slows down an object that slides. • You have to keep pushing to overcome the force of sliding friction.

Sliding Friction, continued • Sliding friction is due to the microscopic roughness of two surfaces. • A force must be applied to move the rough areas of one surface past the rough areas of the other. • What are some examples of sliding friction you encounter in your everyday life?

Rolling Friction • ROLLING FRICTION, occurs between the ground and the part of the tire touching the ground. • Rolling friction keeps the tire from slipping on the ground and exerts force on the tires that pushes the object forward.

Rolling Friction, continued • Why does a cart have wheels? • It’s usually easier to pull a load on a wagon or cart that has wheels rather than drag the load along the ground. • Rolling friction between the wheels and the ground is LESS than the sliding friction between the load and the ground.

Fluid Friction • FLUID FRICTION occurs between an object and air or water. • Examples: • skydivers jump out of a plane • boat traveling through water

ANSWER THE FOLLOWING SELF CHECK QUESTIONS:

Question List and give an example of the four types of friction:

Question List and give an example of the four types of friction: Answer • Rolling Friction (roller skates) • Sliding Friction (plate sliding across a table) • Static Friction (pushing a desk) • Fluid Friction (a person swimming through the water)