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Examples of Forces
Students should be able to:
- identify contact/noncontact forces that affect motion of an object (e.g., gravity, magnetism and friction).
Magnetism: A Non-contact Force
You have learned that gravity is a non-contact force, or a force exerted on an object that does not make contact with it. Gravity pulls down on objects as they move. Another example of a non-contact force is magnetism.
You have probably played with magnets before. Every magnet has two ends, or poles. One end is called the north pole and the other is known as the south pole. If you have two magnets you can see how the poles of the magnets exert forces on each other. Whenever you put two north poles together, the magnets will push apart. This will also happen with two south poles. However, if you put opposite poles together, north and south, the magnets will pull together. Each of these situations is an example of a non-contact force. The magnets exert a force on each other even though they are not touching.
You can how this works by using your mouse to drag the magnets in the mini-movie below. Notice that the opposite poles are facing each other. This means a force will pull the magnets together. The force will keep them together even you try to pull them apart.
Friction: A Contact Force
When two surfaces rub together, they exert a force on each other called friction. You can feel friction when you rub your hands together. When the tires of your parents' car roll over the road friction occurs. In fact, the car could not move without friction. Without it, the tires would spin in place. Because the cars must touch the road for friction to occur, it is an example of a contact force.
Look at the wheel rolling along the road below. Where is friction occuring?
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