identify contact/noncontact forces
that affect motion of an object (e.g., gravity, magnetism and
collision).
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 clicking on the buttons 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.
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?
