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Chapter 20 Science General Knowledge (8)
The sun, the moon, the planets, and other objects in space all have gravity. The pull of the sun is greater than that of the earth because the sun is so much bigger. The diameter of the sun is about 109 times the diameter of the earth. The gravity of the sun keeps the planets orbiting the sun. If there were no gravity pulling them toward the sun, they would spin off into space in a straight line. Scientists have learned about the laws of gravity and about the positions of the planets. They are now able to tell just where each planet is in space at any one time.
The laws of gravity were first discovered by Sir Isaac Newton. He said the idea came to him while he was in the garden drinking tea. An apple fell to the ground at his feet. He realized that the same force which drew the apple to the The ground keeps the moon in its orbit around the earth.
While scientists know about the laws of gravity and how they work, they do not yet know or understand the cause of gravity. Why one body in the universe attracts another is still a mystery to them. The great mysterious forces which regulate the universe and the billions of galaxies out in space and keep them moving in perfect order can only be the work of our great God who created everything. He alone understands why the sun, the moon, the planets, and the billions and billions of galaxies move in such perfect order.
Vocabulary
mighty ["maiti] adj. powerful, powerful;

adv. very, very
diameter [dai"? mit?] n. diameter, magnification
Straight [streit] adj. Straight, straight, uninterrupted, straightforward;

adv. directly, directly
Orbit ["?: bit] n. Orbit;

vt. & vi. run on... orbit, orbit around

mystery ["mist? ri] n. mystery (sex), secret (sex), mysterious thing, people of unknown origin

galaxy ["ɡ? l? ksi] n. Galaxy, Milky Way, a group of (outstanding or famous people)

Practice
Complete these sentences.
1. Gravity is the force, or pull, that keeps us from falling off the .
2. The pull of the sun is greater than that of the earth because the sun is than the earth.

3. The of the sun keeps the planets revolving around the sun.

4. The laws of gravity were first discovered by in the year 1687．

5. The force of gravity on the earth causes everything to be pulled toward the of the earth.

6. The diameter of the sun is about times that of the earth.

7. If there were no gravity pulling the planets toward the sun, they would move off into .
8. Scientists are able to tell where the planets are in at any one time.

Write true or false.
1. The earth is the only planet that has gravity.

2. The gravity of the sun keeps the planets orbiting the sun.

3. The laws of gravity were first discovered by Newton in 1927．

4. Scientists understand all about why one body in the universe attracts another one.

5. The idea of ​​gravity came to Sir Isaac Newton while he was asleep.

6. Scientists still have much to learn about gravity.

7. Gravity causes things to have weight.

Translation
The law of gravity was discovered by Isaac Newton in 1687.He discovered that everything was held together and moved by a strange force.This force is called gravity, and it is a natural force that brings objects closer together.Even so, before 1687, the Bible said that it was God who by his mighty power held the whole world together.

Some things are light weight and some things are heavy.Gravity pulls everything on the earth to the center of the earth. Because of gravity, you can have weight, and because of gravity, you can live on the surface of the earth instead of flying away from the earth.

The sun, moon and planets in space all have gravity.Because the sun is larger than the earth, the pulling force of the sun is greater than that of the earth.The diameter of the sun is 109 times that of the earth, and the gravity of the sun makes all the planets revolve around the sun.If there is no sun's gravity to pull other planets, these planets will fly to other space in a straight line.Scientists already know the laws of gravity and the positions of planets, but they can only know where a planet is in space at any given time.

The law of gravity was first discovered by Isaac Newton.According to Newton, his inspiration came from an accidental discovery.While he was drinking tea in the garden, an apple fell from a tree and hit his foot.He realized that it was the force that made the apple fall to the ground that kept the moon orbiting the earth in its orbit.

While scientists know the law of gravity and how it works, they still don't know or understand what causes gravity.They also cannot understand why something in the universe is attracted to another thing.This great mysterious force controls everything in the universe and thousands of galaxies in space, and makes them fly in space regularly, all of which can only be done by God who created all things.And only God knows why the sun, moon, planets and thousands of galaxies fly so orderly and perfectly.

Exercise
Complete the following sentences.

1.Gravity is the pressure or gravitational force that keeps us from flying away.

2.The gravitational force of the sun is stronger than that of the earth, that is because the sun is stronger than the earth.

3.The sun makes the planets revolve around the sun.

4.The law of gravity was first discovered in 1687.

5.Gravity pulls everything on Earth toward Earth.

6.The diameter of the sun is twice the diameter of the earth.

7.Without the sun's gravitational pull on the planets, they would all be separated from the sun.

8.Scientists can tell where a planet is at any time.

True or false.

1.Earth is the only planet with gravity.

2.The sun's gravity keeps the planets orbiting the sun.

3.The law of gravity was first discovered by Isaac Newton in 1927.

4.Scientists know why one object in the universe attracts another.

5.Gravity was inspired by the dreams of Isaac Newton.

6.Scientists have much more to learn about gravity.

7.Gravity is what gives objects weight.

Finish the sentence:

1. earth 2． bigger 3． gravity
4. Isaac Newton 5． center 6
7. space8． space
True or false:

1. false 2． true 3． false
4. false 5． false6. true
7. true
08 Magnetism magical magnetism

Man has used magnets and the forces that surround them to do many kinds of work. From your study of magnetism, you will remember that magnets are pieces of metal that have the power to attract other materials to themselves. Iron and steel are called magnetic materials because they are attracted to a magnet. Anything that has iron or steel in it can be attracted to a magnet.
Magnetism and electricity are closely related. A way of producing electricity has been discovered by using special magnets. If a magnet is moved near a wire, an electric current is made in the wire. If a wire is moved near a magnet, an electric current is also made.
In 1820 a Danish man named Hans Christian Oersted made a discovery. He discovered that a compass needle jumped when electric current was flowing through a wire held close to the compass. Oersted proved that electricity was affecting the magnet. Electromagnets are used in many ways today. When an electromagnet is attached to a crane, it can be used as a lifting magnet. When the current flows through the coil, the crane can pick up a heavy load. When the current is broken, the load is dropped.
Small electromagnets are also used in many ways in homes, factories, and offices. An electric doorbell is an example of an electromagnet at work.
A machine that makes electricity in large amounts is called a generator. After power is generated in the power plant, it leaves the generator through wires. The wires connect with other wires leading to other parts of the country. Some wires are strung on huge poles ; others are laid underground.
Vocabulary
Magnet ["m?ɡnit] n. Magnets, magnets, attractive people (things)
Steel [sti: l] n. steel, steel;
vt. make strong, firm
Compass ["k?mp?s] n. compass, compass, compass, limit

Needle ["ni:dl] n. needle, needle
Crane [krein] n. Crane, crane, crane;
vt. & vi. elongation, probe

coil [k? il] n. (one) roll, (one) circle, coiled thing, coil;
vt. & vi. roll... into a circle or spiral
load [l? ud] n. load, burden, loading, load, workload, load;

vt. & vi. put...on the car
Electromagnet [i"lektr?u"m? ɡnit] n. (object) electromagnet, electromagnet
generator ["d? en? reit?] n. generator, generator
Practice
Write true of false.
1. A generator is a machine that makes electric power.

2. Magnetism is a force of nature that can be seen easily.

3. Almost any type of material can be attracted by a magnet.

4. Electricity and magnetism are closely related.

5. Cranes can use electromagnets for lifting heavy loads.

6. Electricity can only travel on a closed or complete circuit．

Translation
(End of this chapter)