Friction and Gravitational Interactions

Friction and Gravitational Interactions

Middle School

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Learning Objectives

• Define friction and identify the factors that affect it.

• Distinguish between the four main types of friction: static, sliding, rolling, and fluid.

• Explain the law of universal gravitation and the factors that influence gravitational force.

• Differentiate between mass and weight, and describe how they are related.

• Describe the relationship between an object's kinetic energy, its mass, and its speed.

Key Vocabulary

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Friction

The force that two surfaces exert on each other when they rub, which opposes the motion.

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Gravity

A noncontact force that pulls objects toward each other, depending on their mass and their distance apart.

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Static Friction

The force acting on stationary objects, preventing them from moving when a force is applied to them.

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Sliding Friction

The force produced when two solid surfaces slide past one another, causing moving objects to decelerate.

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Rolling Friction

The force that acts on an object when it is rolling over a surface, slowing it down.

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Fluid Friction

The force that occurs when an object moves through a fluid like water, air, or oil.

Key Vocabulary

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Universal Gravitation

The law that gravity acts between all objects in the universe that possess mass.

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Mass

A measure of the amount of matter in an object, which remains constant regardless of location.

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Weight

A measure of the force of gravity on an object, which changes with the gravitational field.

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Kinetic Energy

The energy an object has due to its motion, depending on both its mass and speed.

What is Friction?

• Friction is a force that opposes an object's motion.

• It occurs when two surfaces rub against each other.

• Friction depends on surface type and the force pressing them together.

Multiple Choice

Which statement best defines friction?

• A force that causes an object to speed up

• A force that opposes the motion of an object

• A force that only exists in outer space

• A force that changes an object's mass

Multiple Choice

What two conditions determine the amount of friction?

• The object's speed and its direction of motion

• The object's color and its temperature

• The texture of the surfaces and the force pressing them together

• The size of the object and the air pressure

Multiple Choice

If a student is pushing a heavy box, which of the following changes would most likely increase the force of friction?

• Pushing the box across a carpeted floor instead of a tile floor

• Lifting the box instead of pushing it

• Removing some weight from inside the box

• Pushing the box more slowly

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The Four Types of Friction

• Static friction acts on objects at rest that you must overcome to move them.

• Sliding friction occurs when two solid surfaces slide over one another, causing slowing.

• Rolling friction happens when an object like a wheel rolls across a surface.

• Fluid friction, like air resistance, is when an object moves through a liquid or gas.

Multiple Choice

Which of the following situations is an example of static friction?

• A book resting on a desk

• A sled moving down a snowy hill

• A bicycle wheel turning on the road

• A swimmer moving through water

Multiple Choice

How can sliding friction be distinguished from rolling friction?

• Sliding friction occurs between two solid surfaces, while rolling friction involves a round object on a surface.

• Sliding friction involves fluids, while rolling friction involves stationary objects.

• Sliding friction slows objects down, while rolling friction speeds them up.

• Sliding friction requires air, while rolling friction requires water.

Multiple Choice

A cyclist is riding a bike along a flat, paved road. Which two types of friction are most significantly acting on the bike and cyclist?

• Rolling friction on the pavement, then fluid friction in the air.

• Static friction on the pavement, then sliding friction in the air.

• Sliding friction on the pavement, then rolling friction in the air.

• Fluid friction on the pavement, then static friction in the air.

The Force of Gravity

• Gravity is a noncontact force that pulls all objects with mass together.

• The gravitational force between objects increases with their mass.

• As distance increases between objects, the gravitational force between them decreases.

Multiple Choice

Which statement best defines the force of gravity?

• A force that pushes all objects with mass away from each other.

• A force that only affects objects when they are touching.

• A force that pulls all objects with mass toward each other.

• A force that exists only between planets and stars.

Multiple Choice

What would happen to the gravitational force between two objects if the mass of both objects were increased?

• The gravitational force between them would decrease.

• The gravitational force between them would increase.

• The gravitational force would disappear completely.

• The gravitational force would not be affected by their mass.

Multiple Choice

Which of the following scenarios would produce the greatest gravitational force?

• Two objects with large masses that are very far apart.

• Two objects with small masses that are very close together.

• Two objects with large masses that are very close together.

• Two objects with small masses that are very far apart.

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Weight, Mass, and Energy of Motion

Mass vs. Weight

• Mass is the amount of matter in an object, measured in kilograms (kg).

• An object's mass is constant and does not change based on its location.

• Weight is the force of gravity on an object, measured in Newtons (N).

Kinetic Energy

• Kinetic energy is the energy an object has because of its motion.

• The amount of kinetic energy depends on an object's mass and its speed.

• An object with more mass or greater speed has higher kinetic energy.

Multiple Choice

Which statement correctly describes the difference between mass and weight?

• Mass is the force of gravity on an object, while weight is the amount of matter in it.

• Mass is the amount of matter in an object, while weight is the force of gravity on it.

• Mass and weight are both measures of the amount of matter in an object.

• Mass is measured in Newtons, while weight is measured in kilograms.

Multiple Choice

What is the relationship between an object's mass, speed, and kinetic energy?

• An object's kinetic energy decreases as its mass increases.

• An object's kinetic energy is not affected by its speed.

• An object's kinetic energy increases as its mass or speed increases.

• An object's kinetic energy depends only on the force of gravity.

Multiple Choice

A large truck is driving on a highway and then slows down to a stop. Which statement best describes what happens to the truck's mass and kinetic energy?

• The truck's mass decreases, and its kinetic energy also decreases.

• The truck's mass remains constant, while its kinetic energy increases.

• The truck's mass remains constant, while its kinetic energy decreases.

• The truck's mass increases, while its kinetic energy remains constant.

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Common Misconceptions

Misconception	Correction
Friction only exists to slow things down.	It is the force that allows us to walk and grip objects.
Mass and weight are the same.	Mass is the amount of matter; weight is the force of gravity.
There is no gravity in space.	Astronauts are in a constant state of free-fall around the Earth.

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Summary

• Friction is a contact force that opposes the motion between two surfaces.

• The four types of friction are static, sliding, rolling, and fluid.

• Gravity is a non-contact force of attraction between any two objects with mass.

• Gravitational force is stronger with more mass and weaker with more distance.

• Mass is the amount of matter, while weight is the force of gravity on an object.

• An object's kinetic energy depends on both its mass and its speed.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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