Contact and Non-Contact Forces

Contact and Non-Contact Forces

Middle School

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Learning Objectives

• Define force and differentiate between contact and non-contact forces.

• Identify and describe various types of contact forces, including friction, muscular force, and normal force.

• Identify and describe various types of non-contact forces, including gravitational, magnetic, and electrostatic forces.

• Explain the factors that influence the strength of forces like gravity and friction.

Key Vocabulary

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Force

A force is a push or a pull on an object, which is measured in Newtons.

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Contact Force

This is a type of force that acts only when two objects are physically touching each other.

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Non-Contact Force

This force can act between two objects that are not in direct physical contact with each other.

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Friction

Friction is a contact force that opposes the motion between two surfaces touching each other.

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Gravity

Gravity is a non-contact force that pulls objects toward each other depending on their mass.

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Types of Forces

Contact Forces

• ​These are forces that act on an object through direct physical touch.

• ​​For the force to have an effect, the objects must be touching.

• ​Kicking a soccer ball is an example of a contact force.

Non-Contact Forces

• ​These forces can push or pull an object without physically touching it.

• ​​They can act from a distance, so the objects do not need to touch.

• ​A magnet pulling paper clips is an example of a non-contact force.

Multiple Choice

Which of the following statements best distinguishes between the two main types of forces?

• Contact forces are pushes, while non-contact forces are pulls.

• Contact forces are measured in Newtons, while non-contact forces are not.

• Contact forces require objects to touch, while non-contact forces can act from a distance.

• Contact forces are always stronger than non-contact forces.

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Types of Contact Forces

• Muscular force is made by your body for movement and even breathing.

• An applied force is a direct push or pull, like pushing a cart.

• Normal force is the support a surface gives to an object on it.

• Tension pulls through a rope; spring force restores a spring’s original shape.

Multiple Choice

A book is resting on a table. Which contact force is exerted by the table to support the book?

• Applied Force

• Normal Force

• Muscular Force

• Tension Force

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The Force of Friction

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

• It is caused by irregularities on surfaces, even ones that seem smooth.

• Air resistance is friction that pushes on objects moving through the air.

• Friction can be helpful by providing grip or cause wear on machine parts.

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Multiple Choice

What is the primary reason friction occurs between two surfaces?

• The irregularities on the surfaces that are touching.

• The magnetic properties of the materials.

• The air pressure between the surfaces.

• The temperature of the surfaces.

Non-Contact Forces

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Gravitational Force

• ​This force pulls all objects with mass toward one another.

• ​​Its strength depends on the mass of the objects and their distance.

• ​An object's weight is the measure of gravity's force on it.

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Magnetic Force

• ​This force acts between magnets and certain metals like iron.

• ​​Every magnet has a north pole and a south pole.

• ​Opposite poles attract, while like poles will repel each other.

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Electrostatic Force

• ​This is the push or pull between electrically charged objects.

• ​​Objects can have a positive or a negative electric charge.

• ​Like charges repel, while opposite charges will attract one another.

Multiple Choice

The strength of the gravitational force between two objects is determined by which two factors?

• Their magnetic poles and distance.

• Their electrical charges and distance.

• Their mass and distance.

• Their mass and electrical charges.

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Common Misconceptions

Misconception	Correction
An object at rest has no forces acting on it.	An object at rest has balanced forces acting on it.
Friction is always a negative force.	Friction is essential for daily activities like walking and writing.
Gravity only pulls objects downward.	Gravity is a universal force between any two objects with mass.

Multiple Choice

How does the function of a normal force differ from the function of a tension force?

• A normal force opposes motion, while a tension force causes motion.

• A normal force depends on mass, while a tension force depends on friction.

• A normal force supports an object on a surface, while a tension force is transmitted through a rope or string.

• A normal force is a non-contact force, while a tension force is a contact force.

Multiple Choice

A skydiver is falling towards Earth. What are the primary upward and downward forces acting on the skydiver?

• Upward: Air resistance, Downward: Gravitational force

• Upward: Normal force, Downward: Applied force

• Upward: Magnetic force, Downward: Muscular force

• Upward: Tension force, Downward: Frictional force

Multiple Choice

When a skydiver jumps from an airplane, they speed up at first but then begin to slow down before opening the parachute. Which force is pushing upward against the skydiver as they fall?

• Air resistance

• Gravity

• Magnetic force

• Electric force

Multiple Choice

If a planet with double the mass of Earth was discovered, what could you predict about the gravitational force it exerts compared to Earth, assuming all other factors are equal?

• The gravitational force would be the same as Earth's.

• The gravitational force would be double that of Earth's.

• The gravitational force would be four times that of Earth's.

• The gravitational force would be half that of Earth's.

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Summary

• A force is a push or a pull, measured in Newtons.

• Forces are either contact (requiring touch) or non-contact (acting at a distance).

• Contact forces include friction, tension, and muscular force.

• Non-contact forces include gravity, magnetic, and electrostatic forces.

• Gravity depends on mass and distance, while friction depends on surface texture.

• Understanding forces helps explain why objects move or stay still.

Poll

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

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