Magnetic Forces | 磁力

📚 Magnetic Forces | 磁力

Magnetic forces are pushes or pulls that magnets exert on certain materials and on other magnets. In KS3 CIE Electromagnets topic 2.2.2, you explore how these forces act without touching, why some materials respond strongly, and how electromagnets use the same magnetic force in circuits.

磁力是磁体对某些材料和其他磁体施加的推力或拉力。在 KS3 CIE 电磁铁主题 2.2.2 中，你将探究这些力如何在不接触的情况下产生作用、为什么有些材料反应强烈，以及电磁铁如何在电路中利用相同的磁力。

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1. What Are Magnetic Forces? | 什么是磁力？

A magnetic force is a non-contact force caused by magnets. It can attract some metals such as iron, nickel and cobalt, and it can attract or repel another magnet. Because it acts at a distance, you do not need to touch a paperclip to a magnet for it to be pulled.

磁力是由磁体产生的一种非接触力。它可以吸引铁、镍、钴等金属，也可以吸引或排斥另一个磁体。由于它在一定距离外就能起作用，你不需要把回形针碰到磁体，它就会被拉动。

Magnetic force has both size and direction. Its size depends on the strength of the magnet and the distance from it, while its direction depends on which poles are facing each other.

磁力既有大小又有方向。它的大小取决于磁体的强度和离磁体的距离，而方向取决于相对的是哪两个磁极。

The unit of force is the newton (N), and magnetic force is also measured in newtons. For small magnets, the force may be only a fraction of a newton, but industrial electromagnets can create forces large enough to lift thousands of kilograms.

力的单位是牛顿（N），磁力也以牛顿为单位。对于小磁体，力可能只有一牛顿的几分之一，而工业电磁铁可以产生足以提起数千千克的力。

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2. Magnetic Poles and the Force Law | 磁极与力的规律

Every magnet has a north pole (N) and a south pole (S). The strongest magnetic force is found at these poles. If you suspend a bar magnet freely, its north pole turns to point roughly towards Earth’s geographic north.

每个磁体都有一个北极（N）和一个南极（S）。磁力最强的位置就在磁极。如果把条形磁铁自由悬挂起来，它的北极会大致指向地球的地理北方。

The basic force law is: like poles repel and unlike poles attract. This means N-N and S-S push apart, while N-S pull together.

基本力的规律是：同名磁极相互排斥，异名磁极相互吸引。也就是说 N-N 和 S-S 会推开，而 N-S 会拉近。

If you break a bar magnet into two pieces, you do not get a separate north piece and a south piece. Each half becomes a new magnet with its own N and S poles. This shows that magnetic poles always exist in pairs.

如果把条形磁铁掰成两段，你不会得到一个单独的北极块和一个南极块。每一半都会变成一个新的磁体，有自己的 N 和 S 极。这表明磁极总是成对出现。

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3. Attraction and Repulsion | 吸引与排斥

When two unlike poles are brought near each other, they experience an attractive force. The magnets may jump together because the force becomes stronger as the gap closes. Many magnetic toys and catches rely on this attraction.

当两个异名磁极靠近时，它们会受到吸引力。磁体可能会突然吸合，因为间隙越小时力越强。许多磁性玩具和门吸都依靠这种吸引力。

When two like poles are brought near each other, they experience a repulsive force. You can feel the resistance as you push two N poles together. This repulsion is used in magnetic levitation and in some suspension systems.

当两个同名磁极靠近时，它们会受到排斥力。当你把两个 N 极推到一起时，会感觉到阻力。这种排斥被用于磁悬浮和一些悬挂系统中。

Attraction and repulsion are both examples of non-contact forces. You can feel them before the magnets touch, which shows that the magnetic field around each magnet is already interacting.

吸引和排斥都是非接触力的例子。你可以在磁体接触之前就感受到它们，这表明每个磁体周围的磁场已经在相互作用。

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4. The Magnetic Field Concept | 磁场概念

A magnetic field is the region around a magnet where magnetic forces can be detected. The field is invisible, but we can map it using iron filings or a small plotting compass.

磁场是磁体周围能够检测到磁力的区域。磁场是看不见的，但我们可以用铁屑或小型绘图罗盘把它描绘出来。

The field is strongest where the field lines are closest together, usually near the poles. Further away from the magnet, the field becomes weaker and the magnetic force decreases.

磁场最强的地方通常靠近磁极，那里磁感线最密集。离磁体越远，磁场越弱，磁力也越小。

We can visualise a magnetic field with a plotting compass. The compass needle aligns with the field direction at each point. By moving the compass around and drawing arrows, we build a field line diagram.

我们可以用绘图罗盘使磁场可视化。罗盘指针会在每一点与磁场方向对齐。通过移动罗盘并画出箭头，我们就能绘制出磁感线图。

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5. Field Lines Around a Bar Magnet | 条形磁铁周围的磁感线

Magnetic field lines are drawn as arrows that point from the north pole to the south pole outside a bar magnet. They never cross each other, and they form closed loops through the magnet from S back to N.

磁感线被画成箭头，在条形磁铁外部从北极指向南极。它们从不交叉，并且通过磁体内部从南极回到北极，形成闭合回路。

Near the poles, the lines spread out from N and curve around to S. If you sprinkle iron filings around a bar magnet, the filings line up along these paths and reveal the pattern.

在磁极附近，磁感线从 N 极散开并弯曲回到 S 极。如果你在条形磁铁周围撒上铁屑，铁屑会沿着这些路径排列，显示出磁场图案。

A uniform magnetic field has parallel, equally spaced field lines. Between two opposite poles of flat magnets, the field is nearly uniform in the centre. In a uniform field, the magnetic force on a north pole has the same strength and direction anywhere in that region.

均匀磁场的磁感线平行且等距。在两块平面磁体的异名磁极之间，中心的磁场几乎是均匀的。在均匀磁场中，北极在该区域任何地方所受磁力的大小和方向都相同。

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6. Magnetic Force and Distance | 磁力与距离

Magnetic force is not constant; it gets weaker as distance increases. If you move a paperclip slowly towards a magnet, you notice that at first nothing happens, then at a certain distance the magnet suddenly pulls it in.

磁力不是恒定的；它随着距离增大而变弱。如果你慢慢地把回形针移向磁体，会发现起初没有反应，到一定距离时磁体会突然把它吸过来。

This is because the field is stronger close to the magnet and weaker far away. A stronger magnetic field produces a larger magnetic force on a magnetic material or another magnet.

这是因为离磁体近的地方磁场强，远的地方磁场弱。磁场越强，对磁性材料或另一个磁体产生的磁力就越大。

You can investigate this by hanging a paperclip from a spring scale and lowering it towards a magnet. Record the reading when the paperclip is just pulled. The closer the magnet, the greater the magnetic force.

你可以通过把回形针挂在弹簧秤上并缓慢靠近磁体来探究这一点。记录回形针刚好被吸引时的读数。离磁体越近，磁力越大。

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7. Magnetic Materials in a Field | 磁场中的磁性材料

Only magnetic materials such as iron, nickel and cobalt are strongly affected by a magnetic field. When iron is placed in a magnetic field, it becomes an induced magnet: its domains align so that it is attracted to the original magnet.

只有铁、镍、钴等磁性材料才会受到磁场的强烈影响。当铁放入磁场中时，它会变成感应磁体：其内部磁畴排列整齐，因此会被原来的磁

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