Introduction to Friction

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Friction 

What is friction?
Friction is a force that happens when two objects rub against each other. It always works in the opposite direction of motion, making it harder for objects to move freely.

1. Effects of Friction

• Slows down motion (example: brakes on a car).

• Changes energy: moving energy (kinetic energy) turns into heat (like rubbing your hands together to get warm).

2. Examples of Friction

• Brakes on a car.

• Shoes rubbing against the ground when running.

• Harder to stop on wet or icy surfaces because friction is less.

3. Reducing Friction

• Use lubricants (oil, grease) in machines.

• Use wheels or balls (rolling friction).

• Use smoother materials (like ice skates on ice).

4. Types of Friction

• Kinetic friction – moving objects.

• Static friction – objects not moving, but still in contact.

• Rolling friction – wheels or balls reduce friction.

• Fluid friction – happens in air or water (airplanes, boats, water slides).

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5. Factors That Affect Friction

• Roughness of surfaces – rough surfaces = more friction.

• Force between objects – stronger push/weight = more friction.

• Coefficient of friction – a number that measures how easily objects slide.

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✅ In short:
Friction is the force that resists motion when objects rub against each other. It can be useful (helping cars stop) or dangerous (slippery roads). We can reduce it with oil, wheels, or smooth surfaces.

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QUIZ

1) Which of the following is considered heat energy?

A: Kinetic

B: Static

C: Dry

D: Thermal

2) Which of the following types of friction occurs when a person rubs their hands together to produce heat?

A: Kinetic

B: Fluid

C: Static

D: Rolling

3) Which of the following types of friction occurs when a boat moves along the surface of water?

A: Kinetic

B: Static

C: Fluid

D: Rolling

4) Which of the following best defines hydroplaning?

A: A boat's surface scrapes the bottom of a body of water

B: Wheels on a car are not in contact with the roadway but moves across water

C: The air resistance felt by an airplane as it moves through the air

D: An airplane moves across the sky through a storm

5) All of the following can reduce friction EXCEPT:

A: Concrete

B: Oil

C: Grease

D: Water

6) Which of the following would have the highest coefficient of friction?

A: Eggs on Teflon

B: Rubber on concrete

C: Ice skates on ice

D: Tires on water