Contact Forces

What is a FORCE?

• A force is a PUSH or a PULL

• Forces are measured in a unit called NEWTONS

• You use a SPRING SCALE to measure force

• Forces are categorized into two groups: CONTACT or NON-CONTACT

Fill in the Blank

A force is a ________ or a ________ exerted on an object.

(only type in the two words that fill in the blank spaces)

Multiple Choice

What is the tool used to measure FORCE?

• balance

• spring scale

• weight

Fill in the Blank

Force is measured in a unit called ____________.

CONTACT FORCES

A force that can cause or change motion of an object by touching it. 

Examples of Contact Forces:

•Applied Force

•Normal Force

•Friction

•Air Resistance

CONTACT FORCES

A contact force is a push or a pull applied by one object to another object that is touching it. Contact forces are also called mechanical forces. 

The image shows a baker pushing his hands into dough, causing the top of the dough to accelerate downward. You can see the baker's hand and dough come into contact with each other.

APPLIED FORCE

An applied force is when one object directly pushes or pulls on another.
For example, pushing or pulling a door, texting or using a phone, writing, stirring a pot when you cook, a tug of war, etc. (Draw one example in your notes.)

Can you think of any other examples of an applied force?

NORMAL FORCE

A normal force is a support force that touches another object which is stable or not moving.
For example, if a book is resting upon a surface like a table, then the surface is exerting an upward force upon the book in order to support the weight of the book. (Draw the picture in your notes.)

Can you think of any other examples of a normal force?

FRICTION

Why does the baseball player slow down as he is sliding towards home plate?
FRICTION!

Friction is a contact force that resists the sliding or forward motion between two objects. The force of friction opposes motion, as seen by the blue arrow in the picture.
Rougher surfaces will produce greater friction, while smoother surfaces reduce the force or friction.

Can you think of any other examples of friction?

FRICTION

Let's put this to the test.

1. Rub your hands together quickly for 15 seconds.

2. Next, apply hand sanitizer, water, or lotion to your hands.

3. Now, rub your hands together quickly for 15 seconds.

Did you notice a difference? What caused this to occur?

AIR RESISITANCE

Would you jump out of a plane without a parachute? Probably NOT!

Air resistance is a type of frictional force that acts upon objects as they travel through the air. As the canopy of the parachute opens, air gets trapped inside. The air pushes up on the parachute, while gravity is pulling you down. The opposing force of the air causes you to slowly fall.

Non-Contact Forces

Identify and/or describe forces acting at a distance such as magnetic, electrical and gravitational.   

Describe and illustrate how electrical charges interact.  

Describe and illustrate how magnetic poles interact. 

• Forces that act on two objects from a distance.

• The objects to not have to touch each other.

• Measured in Newtons (N).

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Non-Contact Forces

Examples of

Multiple Choice

Mars only has about 11% of Earth's mass. What can you conclude about the gravity of these two planets?

• Earth has less gravity because it has more atmosphere

• Mars has less gravity because it has more atmosphere.

• Earth has more gravity because it has more mass.

• Mars has more gravity because it has less mass

Multiple Choice

Why are some forces considered to be noncontact forces?

• Objects must be far apart in order to exert a force.

• Objects push each other apart to increase the distance between them.

• Objects do not have to touch each other to experience a force.

• Objects must be large in size in order to exert a force that is strong enough to notice.

Multiple Choice

All of these are noncontact forces, except

• friction

• gravity

• electricity

• magnetism

• Magnets have two poles, north and south, where the forces are the strongest.

• Opposite poles attract, or pull, on each other.

• Like poles repel, or push away from, each other.

• All magnets have an invisible magnetic field.

• The strength of magnetic forces depend on distance and materials.

​

Magnetic Forces

Multiple Choice

What are two factors that affect the strength of magnetic forces?

• poles and gravity

• distance and material

• distance and direction

• electricity and gravity

Multiple Choice

A magnetic field of a magnet gets _____________ the further magnetic object moves away from the magnet.

• positive

• weaker

• negative

• stronger

• Is a push or pull between charged objects.

• Electrical charge built up on the surface of an objec

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Electric Forces

Multiple Choice

Electrical charge built up on the surface of an object is called _________________.

• current electricity

• lightning

• electrons

• static electricity

Multiple Choice

Sarah is walking around her carpeted bedroom. She notices that when she touches her doorknob to leave, that she feels an electric shock. Which of the following forces is responsible for her observation?

 

• Friction between her socks and the floor

• Gravity between the doorknob and her hand

• Magnetic force between the doorknob and the floor

• Noncontact forces between the carpet and the doorknob

Multiple Choice

Negative and positive charges repel.

• True

• False

• A force that pulls all objects toward each other.

• Gravitational force depends on two factors, mass and distance.

• The more mass an object has, the stronger its gravitational force.

• The greater the distance between two objects, the less gravitational force they exert on each other.

Gravitational Force

Multiple Choice

When the mass increases, the strength of the gravitational field _______.

• increases

• decreases

• stays the same

• constantly changes

• Do Now!!!!!!!!!​

• In your notebook, classify the force that corresponds to that statement.

• Work in groups

• 15 Minutes

Review it

Multiple Choice

When the mass increases, the strength of the gravitational field _______.

• increases

• decreases

• stays the same

• constantly changes

Multiple Choice

What two factors determine the strength of the gravitational force between two objects?

• acceleration and distance

• mass and distance

• speed and distance

• mass and speed

Multiple Choice

Electrical charge built up on the surface of an object is called _________________.

• current electricity

• lightning

• electrons

• static electricity

Multiple Choice

All of these are noncontact forces, except

• friction

• gravity

• electricity

• magnetism

Multiple Choice

What is the type of contact force that is being described?

A foot kicking a soccer ball

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

What is the type of contact force that is being described?

The soccer ball slowing down as it rolls across the field.

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

What is the type of contact force that is being described?

The soccer ball resting on the ground.

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

What is the type of contact force that is being described?

Your hand being pulled backwards as you stick it out of the window of a moving car.

• Applied Force

• Normal Force

• Friction

• Air Resistance

Multiple Choice

What force are you demonstrating when you stand on the ground?

• Gravitational Force

• Friction

• Applied Force

• Normal Force

Multiple Choice

Are forces applied when the objects involved are in direct contact.

• Contact forces

• Normal forces

• action-at-a-distance forces

Multiple Choice

The upward force acting on the parachute is called ______________.

• Force of friction

• Force of gravity

• Normal force

• Air resistance

Multiple Choice

What type of force is being applied to the car by the person?

• applied force

• normal force

Multiple Choice

Friction is a force that acts in an ___________ direction of movement.

• similar
• opposite
• parallel
• west

Multiple Choice

Lyanna decided to rearrange her bedroom by moving her dresser to the opposite wall. She tried pushing it, but found that the dresser would not move. What force was Leanne NOT able to overcome?

• electrical force
• magnetic force
• balanced force
• frictional force