1. What are forces? A push or a pull Gravity Friction Air Resistance
Magnetism
Explore and explain
Discuss clip art.
Click on hyperlink Friction.

2. Two Common Forces Gravity
Unit 7 Lesson 1 What Are Forces?
Two Common Forces
Gravity
Gravity is a force of attraction between two objects. It acts even when objects are not touching.
The size of the force increases as the mass of the objects increases.
The size of the force decreases as the distance between the objects increases.
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3. Gravity: the pull between all objects (the greater the mass, the harder the pull!!!)
Discovered by Sir Isaac Newton when an apple fell upon his head…

4. Friction Friction is a force that opposes motion.
Unit 7 Lesson 1 What Are Forces?
Friction
Friction is a force that opposes motion.
Friction acts between objects that are touching.
Friction produces thermal energy.
Copyright © Houghton Mifflin Harcourt Publishing Company 4

5. Friction: causes motion to slow down or stop… causes drag!
The rough surface of the mountain causes friction and gives us a grip on the side of the mountain when we rock climb.
Friction keeps us from sliding off the skateboard.
The tread on our shoes causes friction, and keeps us from ending up like this guy on icy roads.

6. Air Resistance
Air resistance is a force created by the air. It is a force that opposes motion through the air.
In other words, air resistance pushes back against someone or something moving through the air.
Some objects (like a planes wings or a windshield) are designed to help break wind resistance.

7. A parachute creates even more air resistance
by catching the air slowing the diver down to a
safe speed.
As gravity pushes someone
down to the ground, air resistance
pushes him back up, slowing the fall
A planes wing is designed
to break through air resistance.

8. Magnets A magnet will pull some metals towards itself.
Metals that contain iron, nickel, and cobalt are magnetic. In other words, a magnet will pull them.