Friction What factors determine the strength of the friction force between two surfaces?

Key Terms Friction Static friction Sliding friction Rolling friction Fluid friction

What is Friction? The force that 2 surfaces exert on each other when they rub against each other.

What are the Causes of Friction? The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. Smooth surfaces have less friction; bumpy surfaces have more Friction acts in a direction opposite to the direction of the object’s motion

What is Static Friction? Friction that acts on objects that are not moving Because of static friction, you must use more force to start the motion of stationary objects Once you start an object moving there is no longer static friction

What is Sliding Friction Occurs when 2 solid surfaces slide over each other Examples: spreading sand on icy path Ballet dancers applying resin to ballet slippers so they don’t slip Bicycle brakes Skinning your knee

What is Rolling Friction Occurs when an object rolls across a surface Easier to overcome than sliding friction for similar materials Ball bearings are in moving objects such as skates, skateboards, and bicycles Ball bearings reduce friction by rolling between moving parts

What is Fluid Friction Occurs when solid objects move through a fluid Easier to overcome than sliding friction Reason why moving parts are often bathed in oil or other lubricants Fluid friction occurs between a bicyclist and the air. Bicyclists often wear streamlined helmets and clothes