How Magnets Attract
FoundationA magnet has north and south poles and attracts iron; like poles repel, unlike poles attract, and the force even works through objects.
- Magnets attract objects made of iron.
- A magnet has two poles: north and south.
- Like poles repel; unlike poles attract.
文體小知識：說明文用幾個小實驗揭開磁鐵的秘密：哪些東西吸得住，什麼叫同極相斥。
§Text Passage
1A magnet has an invisible power called magnetic force. It attracts certain things, such as paper clips, pins and iron spoons — most of them made of iron. Wooden rulers, erasers and paper are not attracted, because they contain no iron.
2Every magnet has two poles: north and south. Put the north poles of two bar magnets together and they push apart; put a north pole against a south pole and they grip tightly. This is like poles repel, unlike poles attract.
3Magnetic force works through air, and it can pass through paper, plastic sheets and water. Lay a paper clip on a sheet of paper and slide a magnet slowly beneath — the clip follows as if dancing. But the farther the magnet, the weaker the force.
4Magnets fear knocks and heat; dropped on the floor or left somewhere hot, they grow weak. Handle them gently, keep them away from phones, computers and Octopus cards, and store them safely after the experiment so they do not disturb the appliances.
1Summary 重點摘要
A magnet has north and south poles and attracts iron; like poles repel, unlike poles attract, and the force even works through objects.
2Vocabulary cards Vocabulary
Something that attracts objects made of iron.
The invisible power by which a magnet attracts or pushes objects.
The two strongest ends of a magnet, north and south.
The end of a magnet that points north, often marked red.
The end of a magnet that points south, often marked blue.
To pull another object towards itself.
To push another object away.
A wire clip for papers that a magnet can attract.
A magnet in the shape of a bar, with a pole at each end.
3Step by step Steps
- Step 1: Find what is attractedTo learn what a magnet can do, run a small test first. Line up a paper clip, a pencil, an eraser and an iron spoon, bring the magnet close to each in turn, and record in a table which stick and which do not. The iron paper clip and iron spoon are attracted, while the wooden and plastic things stay still. Some people think a magnet lifts anything, but magnets attract only magnetic materials such as iron — the most basic property of all.
- Step 2: Meet the two polesEvery magnet has two poles, and the pull is strongest at the two ends. To tell them apart easily, paint one end of a bar magnet red for the north pole and the other blue for the south pole; the middle pulls only weakly and can hardly hold a paper clip. Some people think the pull is equal everywhere, yet it is strongest at the ends and weakest in the middle. Remember red north and blue south, and the later experiments will not confuse the poles.
- Step 3: Try like and unlike polesWhen two magnets meet, they sometimes pull together and sometimes push apart. Bring north pole to north pole slowly and your hand feels a push, as if something blocked the way; change to north against south, and the two magnets snap together at once. Some people think magnets only ever attract, but repeating a few times reveals the rule: like poles repel, unlike poles attract — the magnet's most important property, and the very principle that lifts maglev trains.
- Step 4: Attract through an objectMagnetic force is amazing — it can pass through some materials. Rest a thin plastic ruler between two stacks of books, put the magnet under the ruler, and place a paper clip on top; move the magnet below and the clip slides along the ruler, proving the force passed through the plastic. Try thin paper and glass too: some let the force through, thicker ones do not. Some people think magnetic force needs direct contact — this experiment breaks exactly that misconception.
- Step 5: Feel the effect of distanceThe strength of the pull changes with distance. Fix the magnet in place: a paper clip three centimetres away is pulled over as soon as you let go, but at eight centimetres it does not move at all. Measure with a ruler and you will see — the nearer the object, the stronger the pull; the farther, the weaker. Some people think magnetic strength never varies, but distance is the key. When playing with magnets, bring objects very close to hold them firmly.
- Step 6: Look after the magnetsMagnets weaken over time and need good care. After the experiment, lay them flat in a box and do not let them knock against one another; never drop a magnet on the floor or bake it over a fire, for knocks and heat both weaken the magnetism. Some people think magnets are tough, but a single knock can cut their strength sharply. Magnets also disturb phones, TVs and computers, so keep them well away from these appliances.
4Diagrams Diagrams
5Worked example Example
Example: Long used a magnet to pick up paper clips — five in a row. Swapping to a wooden peg, he could not lift even one. Why?
- Magnets attract only magnetic materials such as iron, and do nothing to wood or plastic.
- Paper clips are made of iron, so they cling one after another.
- The wooden peg is wood and contains no iron, so not one can be lifted.
- Try an iron spoon and a copper coin too, record which are attracted, and check the conclusion.
- Answer: A magnet attracts only magnetic materials like iron. Iron paper clips cling firmly, but the wooden peg holds no iron so nothing is lifted; more tests with records will verify the rule.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which two poles does a magnet have?
Q2What happens when like poles meet?
Q3Can a magnet attract a wooden ruler?
Q4Can magnetic force pass through paper?
Q5What happens to the force as the magnet gets farther away?
8Recap Recap
- Magnets attract objects made of iron.
- A magnet has two poles: north and south.
- Like poles repel; unlike poles attract.
- The force works through air and through objects.
- Magnets fear knocks and heat; keep them away from appliances and cards.