Mechanics

Unit 5: Motion and Forces

5.4 Friction

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Fundamentals of physics - Mechanics Friction

---------------------------------------------------------------------------------------- Force of friction acts when surfaces slide or tend to slide over one another. Irregularities on the surfaces in contact causes friction The amount of friction depends on the materials and the force pressing them together. All surfaces have microscopic irregularities that obstruct motion even those which seem to be very smooth. At many points of contact the atoms cling together. Also when one slides over each other another, the objects must rise over the microscopic bumps or scrape off the offending atoms.

Fundamentals of physics - Mechanics Friction

---------------------------------------------------------------------------------------- The direction of the force of friction always opposes the direction of motion. If the crate is pushed to the right, then the friction acts toward the left. The stone falls downward, and air resistance (friction) acts upward .

Walking in water presents a resistance to our motion (friction)

Air Resistance

Weight

Push

Friction

Fundamentals of physics - Mechanics Friction

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Friction does not depend on the area of contact. So those extra wide tires you see on some cars provide no more friction than narrower tires. Give examples of friction that is useful to us and those that cause problems.

So those extra wide tires you see on some cars provide no more friction than narrower ones

Fundamentals of physics - Mechanics Friction

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Summary of Terms

Friction - The resistive force that opposes the motion or attempted motion of an object when surfaces are in contact either with another object or through a fluid.

Friction

Attempted motion