# 2-2 Notes - Types of Forces

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2-2 Notes - Types of Forces
Chapter 2, Lesson 2

Gravity Many types of forces act on objects.
Gravity is an attractive force between all objects that have mass.

Gravity The ball does not travel in a straight line because of the unbalanced force of gravity acting on it.

The Law of Universal Gravitation
The Law of Universal Gravitation states that all objects with mass are attracted to each other. The magnitude of attraction depends on the mass of each object and the distance between them.

The Law of Universal Gravitation
The gravitational force becomes stronger as either or both objects increase in mass. The gravitational force becomes weaker as the distance between the objects increases.

The Law of Universal Gravitation

Weight and Mass Mass is the amount of matter in an object and does not change with location. Weight is the gravitational force on a object and changes with location.

Weight and Mass Weight is a force and a vector.
Weight changes with height above Earth. The gravitational pull of the earth has been mapped in this new geoid image from the GOCE satellite - with the yellows and red indicating a strong pull, while the blues show less gravity. 2011

Weight and Mass

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

Friction A book pushed across a table slows down because of friction.
Friction is an unbalanced force acting on the book to slow it down. MOTION FRICTION

Friction Without friction, you could not walk, drive, skate, etc.
Sometimes we want to INCREASE it. (cleats, surfboard wax)

Static Friction Static friction is the force between two surfaces in contact that keeps them from sliding when a force is applied.

Static Friction A force is applied to a heavy box, but the box doesn’t move.

Static Friction The forces are balanced, the force pushing the box equals the force of static friction pushing in the opposite direction.

Sliding Friction When the force pushing on the box is larger than the maximum static friction force, the box begins to slide. The frictional force that acts on the sliding box is called sliding friction.

Sliding Friction The book pushed across the table slows down because of sliding friction. Without sliding friction, the book would continue moving without a force being applied.

Sliding Friction Usually friction is present and an unbalancing force must be applied to keep an object moving. When friction is greatly reduced, objects move with nearly constant velocity without an applied force.

Rolling & Fluid Friction
Rolling Friction – when an object rolls over a surface. Fluid Friction – when an object moves through a gas OR a liquid (a fluid).

Elastic Forces An elastic force occurs when a material is stretched or compressed. A diving board exerts an upward elastic force on the diver when it is bent downward. 2 types: tension and compression.

Tension Forces A tension force is a pulling force exerted by an object when it is stretched, such as a rubber band.

Compression Forces A compression force is a pushing force exerted by a material when it is squeezed or compressed. The size of the compression force exerted by a material is equal to the size of the force that compresses the material.

Normal Forces A normal force is the force exerted by an object that is perpendicular to the surface of the object.

Normal Forces The cup is exerting a downward force on the table, caused by gravity. The table is exerting an upward normal force on the cup, caused by compression.

2.2 Types of Forces A(n) ____ force is the force exerted by an object that is perpendicular to the surface of the object. A compression B elastic C normal D tension

Which force causes a rolling ball to slow down? A sliding friction
2.2 Types of Forces Which force causes a rolling ball to slow down? A sliding friction B static friction C normal force D gravity

The gravitational force between two objects ____ as ____ increases.
2.2 Types of Forces The gravitational force between two objects ____ as ____ increases. A increases; distance B decreases; mass C increases; velocity D decreases; distance

A B C D If a student pushes a book across a table with a force of 10 N and the force of friction is 2 N, what is the net force on the book? A 0 N B 2 N C 8 N D 12 N

What balanced forces are acting on a book sliding across a table?
SCI 2.d A B C D What balanced forces are acting on a book sliding across a table? A gravity B gravity and friction C sliding friction, normal force, and gravity D gravity and normal force