Physics I-10 Study Guide

Friction

A force that opposes motion

Normal Force

The perpendicular force that presses the two surfaces together at a 90 degree angle

Coefficient of Friction

Mu, the ratio of force of friction to the weight of an object

Kinetic Friction vs Static Friction relation?

Kinetic (Moving) Friction is less than Static (Stationary) Friction

In what direction does friction operate?

In the opposite direction of a moving object

When is weight the same as normal force?

When its on a horizontal surface

Why is static friction greater than kinetic friction

Because irregular surfaces have a chance to settle into each other

What is the basic equation for the force of friction

F = My times Normal Force or Weight

Weight acts in what direction

Downward

Normal Force acts in what direction

Perpendicular to the surfaces

Why does the normal force have to equal the weight of an object when the object rests on a horizontal surface

Because of Newton's third law, equal and opposite forces

Give an example explaining why rolling friction is less than sliding friction

A rolling ball lifts its surface out of the irregularities of the other surface

What are factors on which friction depends

Normal force/the weight of the block, the nature of surfaces involved, and the motion of surfaces

Name the factors on which friction does not depend

Surface area

What must always be present before friction can occur

Two surfaces coming into contact, trying to touch each other/move

What are the products of friction resulting from rubbing your hands together, striking two pieces of flint together, shutting a warped door

Heat, Sparks, noise

What is the relationship between weight and the force of friction

The greater the weight the greater the force of friction

A block is resting on a horizontal surface. What could be done to make the force pressing the surfaces together not equal to the blocks weight? The surfaces must remain in contact

Make the pulling force perpendicular / pull at an angle

Describe how reducing the friction between your shoe sole in the floor would affect walking. What law of physics explains what you just described

Newton's third law, for you to move forward, your shoe has to create a backward force; reducing the friction would make it harder to walk

Explain why the coefficient of friction does not have units of measure

The units divide out

In the lab, how did the normal force change as an angle of incline increased

The force decreased because the scale was lifting more and more of the weight

What is the relationship between angle of an incline to the force of gravity

As the angle of incline increases the effective force of gravity is increased