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FRICTION!!!. Friction = a force that opposes motion between two surfaces that are moving. Friction occurs because the surface of any object is rough . All surfaces consist of microscopic “hills” and “valleys.” When two surfaces are in contact, these hills and valleys interlock .
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Friction = a force that opposes motion between two surfaces that are moving.
Friction occurs because the surface of any object is rough. • All surfaces consist of microscopic “hills” and “valleys.” • When two surfaces are in contact, these hills and valleys interlock.
Two variables that determine the amount of friction between two surfaces: • The roughness of the surfaces. • The force pushing the surfaces together.
Two Rules to Remember: • Rougher surfaces create more friction. (Smooth = less friction) • Greater force creates more friction. (Less force = less friction)
Rougher surfaces create more friction. (Smooth = less friction)
Greater force creates more friction. (Less force = less friction)
4 Types of Friction: • Sliding Friction • Rolling Friction • Fluid Friction • Static Friction
Sliding Friction • Occurs when one object slides across another object. • Sliding friction opposes movement; it acts in the opposite direction of the moving object.
Rolling Friction • Occurs as a wheel or bearing rolls across a surface. • Rolling friction is usually less than the force of sliding friction. • What type of friction occurred between the axle and bearing of your mousetrap car?
Fluid Friction • Fluid friction occurs as an object is traveling through a fluid. • A fluid is a liquid or gas. • In most cases, fluid friction is less than sliding friction.
Static Friction • Static friction is the force that prevents an object from moving. • It balances the applied force trying to move it. • Static friction disappears once the object starts moving.
Friction can help or hurt. • Helpful: • Traction between wheels and road. • When trying to open a soda bottle. • When walking! • Harmful: • Friction converts KE into heat; heat breaks down parts and reduces the efficiency of machines.
How to reduce friction: • Lubricants • Make rough surfaces smoother.
How can you increase friction? • Make surfaces rougher. • Increase the force pushing the surfaces together.