Learn English with American Primary School Textbooks

Chapter 21 Science General Knowledge (9)
Humans do many things with magnets and their magnetic power.Through the study of magnetism, it is found that a magnet is a piece of iron that can attract other substances.Iron and steel are called magnetic substances because they are attracted to magnets, and any substance that contains steel or iron is attracted to magnets.

Magnetism and electricity are closely related, and a method was found to generate electricity using special magnets.If the magnet moves around the wire, a current is generated in the wire.If the wire moves around the magnet, there will also be current in the wire.

In 1820, a Dane named Hans Christian Oersted discovered that a compass needle would move when a live wire was brought close to it.Oersted demonstrated that electrical energy is affected by magnets.Since then, people have made electromagnets.Electromagnets are widely used today, and installing electromagnets on cranes becomes a magnetic crane.By energizing the coil, the crane lifts the load.When the coil is de-energized, the weight falls.

Electromagnets are also widely used in homes, factories, and offices, and a doorbell is an example of an electromagnet application.

A machine that produces electricity in large quantities is called a generator, and the electricity generated in a power plant is output from the generator through wires.The wire connects to other wires that carry electricity across the country, some in the air on poles and some buried in the ground.

Exercise
True or false.

1.A generator is a machine capable of producing electricity.

2.Magnetism is a force of nature that can be found everywhere.

3.Almost all materials can be attracted by magnets.

4.Electricity and magnetism are closely related.

5.Cranes use electromagnets to lift heavy objects.

6.Electric current can only exist in a closed loop circuit.

1. true 2． true3. false
4. true 5． true 6． True
09 Sitting Posture What is the correct sitting posture

What do others see when they look at you? Do you appear confident? Happy? Full of energy? Probably the first thing others see is your posture, or the way you hold your body when you sit, stand, or move about. If you hold your body in the proper sitting and standing positions when you are young, the bones and muscles will grow Properly and correct posture will become a habit—something you do without thinking about it.
When your posture is good, the parts of your body are in position to do the work they should do. Good posture allows the lungs to expand and fill with air. It helps the blood to circulate freely through the body, and it aids in the Digestion of food. When your posture is good, the weight of your body is supported as it should be, and you can sit or stand or walk around without getting tired too soon. Because your bones and good posture work together, it is especially important to have good posture when you are growing.
If you let your body slouch or slump, your lungs, stomach, and other important organs become crowded, and your blood does not circulate well through your body. A lack of oxygen and poor circulation caused by poor posture make your body work harder than it should. Foot problems, back trouble, and headaches may also be caused by poor posture. Only when correct posture habits are used do the parts of the body work together in proper balance and comfort.
Because you spend more time sitting each day than you do standing or walking, your sitting posture is very important! When you are working at a table or desk, you will not get tired as easily if you sit on a straight, hard chair. The chair—instead of your muscles—can do much of the work of keeping your body straight. Sit back on your chair so that your hips touch the back of it. Sit tall with your shoulders pulled back and your back straight. Let your feet rest on the floor with your toes pointed forward. You should not cross your knees while you are sitting, because that causes poor blood circulation. It also throws your body out of balance, causing poor posture. If you have to sit for a long time, it may be relaxing to cross your ankles for a few minutes, but you should return to correct sitting posture. If possible, you should occasionally stand up and stretch. This improves your circulation and helps keep you alert. When you lean forward to get closer to your work, you should not let your shoulders and back slump. Bend from your hips so that your back stays straight. Whenever you find yourself sli Ding too far down into your seat or bending too far forward, you need to straighten up. Poor posture is lazy posture—it gives you a dull, tired feeling that keeps your body and mind from being alert and active. Good posture makes you look better, feel better, and have more energy.
Sitting improperly in a lounge chair can strain your neck and shoulders and cause poor posture. When you sit in a lounge chair, you may want to rest your legs and feet on an ottoman or footstool to help you relax. This also helps your circulation. If you are sitting correctly, your chest will expand easily.
Good posture does not mean stiff, rigid posture. If you are sitting properly, there should be no strain on any part of your body. You should look and feel comfortable.
Vocabulary
Posture ["p? st??] n. posture, posture, attitude;

vt. make a certain gesture
position [p? "zi??n] n. orientation, position, identity, position, posture, position, position

bone [b? un] n. bones, bony objects, bones

Muscle ["m? sl] n. Muscle, muscle tissue, muscle strength
lung [l? ? ] n. Lung;
adj. pulmonary
Circulate ["s?: kjuleit] vt. & vi. (to) circulate, (to) circulate, spread, spread

slouch [slaut? ] vi. To stand, sit, or walk listlessly

slump [sl? mp] vi. to drop sharply, plummet;
n. Depression period, <US> (individual, team, etc.) low tide state

Stomach ["st? m? k] n. Stomach, abdomen, appetite, desire

organ ["?:ɡ?n] n. organ, organ, mechanism

Headache ["hedeik] n. Headache, headache

Straight [streit] adj. Straight, straight, uninterrupted, straightforward;

adv. directly, directly
hip [hip] n. buttocks, buttocks

Shoulder ["??uld?] n. The upper part of the shoulder, shoulder, shoulder, back;
vt. Carry, pick, shoulder...

toe [t? u] n. toes, toes
knee [ni:] n. knee, knee, knee

ankle ["??kl] n. ankle, ankle joint
occasionally [? "kei??n?li] adv. Sometimes, occasionally

stretch [stret? ] vt. & vi. Stretch, stretch, extend;
n. to extend, to extend, to extend

lean [li:n] vt. & vi. (make) tilt, bend down;
vt. Lean on, rely on, rely on;
adj. Thin, barren
slide [slaid] vt. & vi. sliding, sliding;
vi. to slip, fall;
n. glide, slide, slide
dull [d? l] adj. Unclear, unclear, dull, blunt, depressed
alert[? "l?: t] adj. Vigilant, vigilant, clever;

vt. to keep (someone) alert;
n. alert, alert

lounge [laund? ] n. lounge, lounge, living room;
vi. to recline lazily

Strain [strein] vt. & vi. Tighten, use as much as possible, do our best;

n. tension, tense, tense

ottoman n.

Footstool ["futstu: l] n. footstool
chest [t? est] n. Chest, chest cavity, cabinet

stiff [stif] adj. Not easy to bend, stiff, stiff, unfriendly

rigid ["rid? id] adj. rigid, rigid, strict, inflexible, invariable
Practice
1. Sometimes you do without thinking about it is a ．

2. The first thing that others see is .

3. You should sit with back ．

4. When sitting a long time, you should stand up and ．

5. Poor posture will give you and tired feeling.

Translation
When people look at you, what do they see?You act confident?very happy?Energetic?Perhaps the first thing people see is your posture, or the way you sit, stand, or move.When you're young, if you stand and sit with good posture, your bones and muscles will grow normally, and correct posture becomes a habit—things you do without thinking.

When you have good posture, the parts of your body are doing what they are supposed to do.Good posture expands and fills the lungs with air, helps blood circulate freely through the body, and aids in the digestion of food.When your posture is correct, your body weight is supported as it should be so you don't get tired as quickly when sitting, standing or walking.Because your bones and good posture work together, it's even more important when you're growing.

If you keep your body hunched or hunched over, your lungs, stomach, and other vital organs can become congested, and your blood can't circulate well through your body.Lack of oxygen and poor circulation due to poor posture can make your body work harder.Foot problems, back troubles, and headaches can all be caused by poor posture.Only when the posture is correct will the body parts work together in a state of balance and comfort.

Since you spend a lot more time sitting than standing or walking every day, how you sit is very important!When you're working at a desk, sitting in a chair that's upright and firm will make you tire less easily.Chairs -- in place of muscles -- can go a long way toward keeping your body upright.Sit on the chair with the back of the chair so that your buttocks can touch the back of the chair.Sit in a high chair and let your shoulders pull on your back to keep it straight.Rest your feet on the floor with your toes pointing forward.Do not cross one leg over the other when you are sitting, as this can cause poor circulation and throw your body off balance, causing bad posture.If you've been sitting for a long time, cross your ankles for a few minutes to relax, but you should be back to the correct sitting position after a while.You should stand up and stretch occasionally if possible.This will improve your blood circulation and help you stay flexible.When you're leaning forward to work, you can't be hunched over.Bend your hips to keep your back straight.Anytime you find yourself sliding too far out of the chair or bending over for too long, it's time to sit upright.Poor posture is slouching -- it gives you a dull, tired feeling and keeps your body and mind from being flexible and active.Good posture can help you look good, feel good, and feel more energized.

Sitting incorrectly on the couch can strain your neck and shoulders and create poor posture.When you're sitting on the couch, you may want to rest your legs and feet on an ottoman or footstool to help you relax, which will also benefit your circulation.If you can sit properly, your ribcage will expand easily.

Good posture doesn't mean rigid, rigid posture.If you're sitting properly, there shouldn't be any pressure on any part of your body.Whether it looks to others or feels to you, it will be very comfortable.

Exercise
1.Sometimes, the things you do without thinking are.

(End of this chapter)