Uses of Magnets
FoundationFrom fridge magnets to maglev trains, magnets help everywhere: holding, sealing, pointing the way and driving trains.
- Magnets hold, seal, point the way and push.
- Magnets hide in fridge doors and pencil boxes.
- The compass is one of China's Four Great Inventions.
文體小知識：說明文帶你在家中尋找磁鐵的蹤影，再放眼世界，看磁鐵怎樣大顯身手。
§Text Passage
1Magnets can attract iron, and people use this power to make many useful things. Look around your home first: fridge magnets hold notes and drawings; magnetic strips hidden round the fridge door seal it tightly; pencil boxes and handbags open and close with magnetic clasps; and a door stopper behind the bathroom door keeps it from swinging.
2Magnets can also show direction. The little needle in a compass always points one end north. Carry a compass on a hike and you will not get lost even in the woods. The ancient Chinese invented the compass — one of China's Four Great Inventions.
3Magnets can push things too. The principle that like poles repel drives maglev trains: magnetic force lifts the train above the track, touching nothing, so the ride is fast and smooth. Maglev trains can run faster than three hundred kilometres per hour.
4Keep observing and you will find more: magnetic boards hold the teacher's word cards; magnets inside speakers and earphones help make sound; even magic shows often use magnets. Small magnets, mighty powers!
1Summary 重點摘要
From fridge magnets to maglev trains, magnets help everywhere: holding, sealing, pointing the way and driving trains.
2Vocabulary cards Vocabulary
What a thing is used for.
A long hidden magnet that holds iron, set into an edge.
A tool with a magnetic needle for finding direction.
A small needle that swings freely with one end always pointing north.
A train lifted by magnetic force above the track, running at high speed.
To float in the air without touching the ground.
China's four great ancient inventions: paper, printing, gunpowder and the compass.
The device containing a magnet that turns signals into sound.
The distance travelled in one hour, such as three hundred kilometres per hour.
3Step by step Steps
- Step 1: Hunt for magnets at homeMagnets are not confined to the classroom; they hide in many corners of our homes. Hold a paper clip near the edge of the fridge door and you will feel a gentle pull: a magnetic strip is hidden there, keeping the door shut tight. The door stopper behind the front door and the clasp of a pencil box are also the work of magnets. Some people think magnets belong only in the laboratory, but with careful watching you will find their power to attract iron quietly serving our daily life everywhere.
- Step 2: Meet clasps and door stoppersMagnetic clasps and door stoppers are common little uses of magnets. A pencil box snaps shut with a click because the magnetic clasp inside is at work; a stopper behind a door holds the door with magnetic force so it never bangs against the wall, protecting both wall and door. These quiet designs serve us every single day. Some people take them for ordinary metal fittings; once you can tell them apart, you will see that science is everywhere, waiting to be observed.
- Step 3: Learn the compassThe compass is a fine example of magnets helping people find their way. Lay the compass flat on your palm, keep it away from iron and electrical appliances, wait for the needle to settle, and the red end will point north; once north is known, east, south and west follow. Some people think a compass reads truly anywhere, but near iron objects the needle is disturbed and shifts. Hikers who carry a compass will not lose their way even deep in the woods.
- Step 4: Know the maglev trainMagnets do not only pull; they can push as well, and maglev trains make good use of this. Using the principle that like poles repel, the train floats above the track without touching it, so resistance falls and the ride is fast and quiet, at over three hundred kilometres per hour. Some people think magnets can only attract. Knowing the maglev train, we understand that careful study of magnetic force can lead to astonishing inventions.
- Step 5: Uncover the secret of soundEarphones and speakers make sound with a secret that also lies in magnets. Inside an earphone hide a small magnet and a coil; when current flows through the coil it creates changing magnetic force that shakes a thin film rapidly, and the vibration travels through the air to our ears. Some people think music relies on electricity alone, yet the magnet is hard at work too. Understanding this, we find science has always been beside our ears, waiting to be discovered.
- Step 6: Make a small applicationHaving learned what magnets can do, we can build a little application ourselves. Fix a magnetic sheet on the fridge door to make a message board, holding your daily homework list and notes with paper clips; or make a fishing toy and lift paper fish out one by one with a magnet. Some people think science projects are difficult, but the materials are already at home. Making one shows that a magnet is both a useful tool and a playful friend.
4Diagrams Diagrams
5Worked example Example
Example: Yan's hiking group cannot tell directions in the woods, and the leader takes out a compass. Why can a compass show direction, and how is it used?
- Inside the compass is a small magnetic needle that turns under the influence of the Earth's magnetism.
- When the needle comes to rest, its red end steadily points north.
- Hold the compass flat on your palm, away from iron objects, and wait until the needle stands completely still.
- Mark north first, then match it with the map to decide which way to go.
- Answer: The needle inside a compass is moved by the Earth's magnetism, and when it settles one end always points north. Hold it flat away from iron, fix north, and match it with the map to find the right direction.
6Common mistakes Mistakes
7Quick check Quick check
Q1Why does the fridge door close tightly?
Q2Where does one end of the compass needle point?
Q3Which country invented the compass first?
Q4What principle lifts a maglev train?
Q5What does the magnet inside earphones do?
8Recap Recap
- Magnets hold, seal, point the way and push.
- Magnets hide in fridge doors and pencil boxes.
- The compass is one of China's Four Great Inventions.
- Maglev trains levitate by magnetism and run at high speed.
- Keep magnets away from magnetic cards and appliances.