2-2typesofforces

7/30/2019 2-2TypesofForces

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gravity

law of universalgravitation

weight

friction

static friction

elastic forcetension force

2.2 Types of Forces

compression force

normal force

sliding friction

rolling friction

fluid friction


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Gravity

Gravity is an attractive force between allobjects that have mass.

Many types of forces act on objects.

2.2 Types of Forces


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Gravity (cont.)

The ball doesnot travel in astraight linebecause of theunbalancedforce of gravityacting on it.

2.2 Types of Forces


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The Law of Universal Gravitation

The Law of Universal Gravitation statesthat all objects with mass are attracted toeach other.

The magnitude of attraction depends onthe mass of each object and the distancebetween them.

2.2 Types of Forces


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The Law of Universal Gravitation (cont.)

The gravitational force becomes strongeras either or both objects increase in massor move closer together.

The gravitational force becomes weaker as

either or both objects decrease in mass ormove farther apart.

2.2 Types of Forces


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Weight and Mass

Mass is the amount of matter in an objectand does not change with location.

Weight is the gravitational force on a

object and changes with location.

2.2 Types of Forces

Weight is a force and a vector.

Weight changes with height above Earth.


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Friction

Friction is a force that opposes themovement between two surfaces in contact.

A book pushed across a table slows down

because of friction.

Friction is an unbalanced force acting on thebook to slow it down.

2.2 Types of Forces


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Static Friction

Static friction is the force between twosurfaces in contact that keeps them fromsliding when a force is applied.

2.2 Types of Forces

A force is applied to a heavy box, but thebox doesnt move.

The forces are balanced, the force pushingthe box equals the force of static frictionpushing in the opposite direction.


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Sliding Friction

When the force pushing on the box islarger than the maximum static frictionforce, the box begins to slide.

2.2 Types of Forces

The frictional force that acts on the slidingbox is called sliding friction.


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Sliding Friction (cont.)

The book pushed across the table slowsdown because of sliding friction.

Without sliding friction, the book would

continue moving without a force beingapplied.

2.2 Types of Forces


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Sliding Friction (cont.)

Usually friction is present and anunbalancing force must be applied tokeep an object moving.

When friction is greatly reduced, objectsmove with nearly constant velocity without anapplied force.

Rolling friction

Smoother surfaces

Lubricating surfaces

2.2 Types of Forces


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Elastic Forces

An elastic force occurs when a material isstretched or compressed.

A diving board exerts an upward elastic

force on the diver when it is bentdownward.

2.2 Types of Forces


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Tension

A tension force is a pulling force exertedby an object when it is stretched, such as arubber band.

2.2 Types of Forces


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Compression

A compression force is a pushing forceexerted by a material when it is squeezedor compressed.

The size of the compression force exertedby a material is equal to the size of theforce that compresses the material.

2.2 Types of Forces


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Normal Forces

A normal force is the force exerted by anobject that is perpendicular to the surfaceof the object.

2.2 Types of Forces


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Normal Forces (cont.)

The cup is exerting a downward force onthe table, caused by gravity.

The table is

exerting anupward normalforce on the cup,caused by

compression.

2.2 Types of Forces


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2.2 Types of Forces


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2.2 Types of Forces


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Forces in the Horizontal Direction

Friction balances forces applied in ahorizontal direction.

Friction equals the horizontal force on an

object that is not changing motion.

2.2 Types of Forces


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Forces in the Vertical Direction

Upward normal force balances thedownward force of gravity on an object thatis not moving vertically.

2.2 Types of Forces


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Forces in the Vertical Direction (cont.)

2.2 Types of Forces


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A(n) ____ force is the force exertedby an object that is perpendicular tothe surface of the object.

A compression

B elastic

C normal

D tension

2.2 Types of Forces


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Which force causes a rolling ballto slow down?

A sliding friction

B static friction

C normal force

D gravity

2.2 Types of Forces


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The gravitational force between twoobjects ____ as ____ increases.

A increases; distance

B decreases; massC increases; velocity

D decreases; distance

2.2 Types of Forces

2-2typesofforces

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