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# Gravity, Friction, Magnetism

Three well known examples of forces are gravity, friction and magnetism.

Gravity is not just a force on planet Earth. Each planet has its own gravity, and each planet's gravity is different. Here on Earth we measure gravity using a scale. Your weight is the measure of gravity's pull on you. Scientists often like to use the word mass instead of weight. For everyday matters, here on Earth, your weight and your mass are the same, but that is not true everywhere! If you ever become an interplanetary traveler, you will see that your weight is different on each planet. This is because a planet's gravity is determined by its own size, or mass. The force of gravity also depends on how close an object is to the center of the planet.

Friction.What is the difference between socks and sneakers? OK – there are a lot of differences, but one difference is that sneakers have a lot more friction than socks. Friction is the force that happens when two things rub together. The effect of friction is usually to slow you down. With less friction, you can move more easily. With more friction, you have to work harder to move the same distance, because the friction slows you down.

Different kinds of motion give rise to different types of friction between objects. Static friction occurs between stationary objects, while sliding friction occurs between objects as they slide against each other. Other types of friction include rolling friction and fluid friction. The coefficient of friction for two materials may differ depending on the type of friction involved.

Magnetism is the force by which objects are attracted to other objects or repelled by other objects. Magnets have two opposite ends, called poles. The north pole of one magnet will repel, or push away, the north pole of another magnet. The same thing will happen with two south poles. However, the north pole of one magnet will attract, or pull toward itself, the south pole of another magnet ("opposites attract"). Magnetism involves electrons and electricity. This is a complicated topic. Scientists in this field study things like physics, electromagnetic theory, and quantum mechanics. All of these topics depend on advanced mathematics. Electricity is often used to make one type of magnet, called an electromagnet. Electromagnets are made from copper wire coiled around a core. When the current stops, the magnetism stops too. Electromagnets have many practical uses. They are used in relays and switches, computer disc drives, tape drives, speakers, and power door locks. MRI machines in hospitals use magnetism to make a picture of the inside of your body.

1. Magnetism produces electrons and electricity.

2. Different kinds of motion give rise to similar types of friction between objects.

3. Electromagnets as a rule have different practical uses.

4. Electricity is seldom used to make one type of magnet, called an electromagnet.

5. The force of gravity also depends on how close an object is to the pole of the planet.

6. Here on Earth we produce gravity using a scale.

7. Your height is the measure of gravity's pull on you.

Date: 2015-12-11; view: 1581

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