Category Forces in Action, Forces in Motion


In Japan, “maglev” trains run just above, not on, their tracks. Both the bottom of the train and the track itself are magnetic. The magnets repel each other, so the train hovers just above the track, enabling it to run with less friction and so reach higher speeds.

Maglev trains incorporate a basic fact about magnetic forces—like magnetic poles repel each other, and opposite magnetic poles attract each other—to lift, propel, and guide a vehicle over a track (or guideway). Maglev train propulsion and levitation may involve the use of superconducting materials, electromgnets, diamagnets, and rare-earth magnets.

Two types of maglev trains are in service. Electromagnetic suspension (EMS) uses the attractive force between magnets present on the train’s sides and underside and on the guideway to levitate the train. A variation on EMS, called Transrapid and used in Germany, employs an electromagnet to lift the train off the guide way. The attraction from magnets presents on the underside of the vehicle that wraps around the iron rails of the guideway keep the train about 1.3 cm (0.5 inch) above the guideway.

Electrodynamic suspension (EDS) systems are similar to EMS in several respects, but the magnets are used to repel the train from the guideway rather than attract them. These magnets are supercooled and superconducting and have the ability to conduct electricity for a short time after power has been cut. (In EMS systems a loss of power shuts down the electromagnets.) Also, unlike EMS, the charge of the magnetized coils of the guideway in EDS systems repels the charge of magnets on the undercarriage of the train so that it levitates higher (typically in the range of 1–10 cm [0.4–3.9 inches]) above the guideway. EDS trains are slow to lift off, so they have wheels that must be deployed below approximately 100 km (62 miles) per hour. Once levitated, however, the train is moved forward by propulsion provided by the guideway coils, which are constantly changing polarity owing to alternating electrical current that powers the system.

Maglev trains eliminate a key source of friction—that of train wheels on the rails—although they must still overcome air resistance. This lack of friction means that they can reach higher speeds than conventional trains. At present maglev technology has produced trains that can travel in excess of 500 km (310 miles) per hour. This speed is twice as fast as a conventional commuter train and comparable to the TGV (Train à Grande Vitesse) in use in France, which travels between 300 and 320 km (186 and 199 miles) per hour. Because of air resistance, however, maglev trains are only slightly more energy efficient than conventional trains.

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The earth’s north and South Poles attract charged particles from the Sun. Within the atmosphere, these collide with molecules of gas to cause spectacular light shows, called the aurora borealis (northern dawn), which can be seen in the Arctic Circle.  When the weather conditions are right, the aurora borealis, also known as the northern lights, can sometimes be seen outside the Arctic Circle in the northern hemisphere.

Our sun is 93 million miles away. But its effects extend far beyond its visible surface. Great storms on the sun send gusts of charged solar particles hurtling across space. If Earth is in the path of the particle stream, our planet’s magnetic field and atmosphere react. When the charged particles from the sun strike atoms and molecules in Earth’s atmosphere, they excite those atoms, causing them to light up.

What does it mean for an atom to be excited? Atoms consist of a central nucleus and a surrounding cloud of electrons encircling the nucleus in an orbit. When charged particles from the sun strike atoms in Earth’s atmosphere, electrons move to higher-energy orbits, further away from the nucleus. Then when an electron moves back to a lower-energy orbit, it releases a particle of light or photon.

What happens in an aurora is similar to what happens in the neon lights we see on many business signs. Electricity is used to excite the atoms in the neon gas within the glass tubes of a neon sign. That’s why these signs give off their brilliant colors. The aurora works on the same principle – but at a far more vast scale.

The aurora often appears as curtains of lights, but they can also be arcs or spirals, often following lines of force in Earth’s magnetic field. Most are green in color but sometimes you’ll see a hint of pink, and strong displays might also have red, violet and white colors. The lights typically are seen in the far north – the nations bordering the Arctic Ocean – Canada and Alaska, Scandinavian countries, Iceland, Greenland and Russia. But strong displays of the lights can extend down into more southerly latitudes in the United States. And of course, the lights have a counterpart at Earth’s south Polar Regions.

The colors in the aurora were also a source of mystery throughout human history. But science says that different gases in Earth’s atmosphere give off different colors when they are excited. Oxygen gives off the green color of the aurora, for example. Nitrogen causes blue or red colors.

So today the mystery of the aurora is not, so mysterious as it used to be. Yet people still travel thousands of miles to see the brilliant natural light shows in Earth’s atmosphere. And even though we know the scientific reason for the aurora, the dazzling natural light show can still fire our imaginations to visualize fire bridges, gods or dancing ghosts.

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The fact that an electromagnet ceases to become a magnet when the current is turned off can be used to great effect in large and small machines. For example, a powerful magnet can lift very heavy weights of iron and steel in a factory, but that would be no good if the magnet could not be persuaded to release them. With an electromagnet, the current can be stopped and the load released.

Magnets come in two main types: permanent magnets and electromagnets. As its name suggests, a permanent magnet is always magnetized — think of a kitchen magnet that stays stuck to a refrigerator door for years. An electromagnet is different; its magnetism works only when powered by electricity. Although an electromagnet is more complicated than a permanent magnet, it has useful and important advantages.

One of the most important features of an electromagnet is the ability to change its magnetic force. When no electric current flows through the magnet’s wires, it has no magnetic force. Put a little current in the magnet, and it has a small force. A large current gives the magnet a bigger force, able to lift or pull heavier objects. The ability to turn magnetic force on and off has many important uses, ranging from simple household gadgets to giant industrial machines.

The pulling power of a permanent magnet is limited to the type of metal from which it’s made. Currently, the strongest permanent magnets are made of a combination of iron and a metal called neodymium. Although these permanent magnets are strong, the best electromagnets are more than 20 times stronger.

Small electromagnets are used in electronic locks, such as those found on an automobile or the main door of an apartment building. Scrapyard cranes have powerful electromagnets that lift metal car bodies with ease. Magnetic Resonance Imaging machines use very powerful electromagnets to produce highly detailed images of the human body. The strongest electromagnets are those used in scientific research to study the properties of matter.

An electromagnet can save people who live up several flights of stairs from having to walk down to the front door when the bell rings. They can simply find out who is calling by means of an intercom and then press a switch to let the caller in. The switch turns on a current that activates an electromagnet. The magnet attracts the door latch, pulling it back and allowing the visitor to enter. Then a spring allows the latch to slip back into place.

You can find small permanent magnets in toys, handheld gadgets such as electric razors, and clasps for bracelets and watches. Larger permanent magnets are useful in household appliance motors and in stereo speakers. The electric motors in hybrid vehicles use very strong permanent magnets.

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The earth has a core of molten iron and is itself a huge magnet. Its magnetic field acts as though there were a bar magnet running along the axis of the Earth. A compass contains a magnetized needle, which can turn freely. No matter which direction the compass is facing, the needle will turn to point towards the North Pole. The compass can then be rotated so that its north point lines up with the needle and the other directions can be read.

If you’re lost in the woods, your best chance of finding your way might be a tiny magnet. A magnet is what makes a compass point north — the small magnetic pin in a compass is suspended so that it can spin freely inside its casing and respond to our planet’s magnetism. A compass needle aligns itself and points toward the top of Earth’s magnetic field, giving explorers and lost souls a consistent sense of direction.

A compass points north because ll magnets have two poles, a north pole and a south pole, and the north pole of one magnet is attracted to the south pole of another magnet. (You may have seen this demonstrated by a pair of simple bar magnets or refrigerator magnets pushed end to end.)

The Earth is a magnet that can interact with other magnets in this way, so the north end of a compass magnet is drawn to align with the Earth’s magnetic field. Because the Earth’s magnetic North Pole attracts the “north” ends of other magnets, it is technically the “South Pole” of our planet’s magnetic field.

While a compass is a great tool for navigation, it doesn’t always point exactly north. This is because the Earth’s magnetic North Pole is not the same as “true north,” or the Earth’s geographic North Pole. The magnetic North Pole lies about 1,000 miles south of true north, in Canada.

And making things even more difficult for the compass-wielding navigator, the magnetic North Pole isn’t even a stationary point. As the Earth’s magnetic field changes, the magnetic North Pole moves. Over the last century, it has shifted more than 620 miles (1,000 kilometers) toward Siberia, according to scientists at Oregon State University.

This difference between true north and the north heading on a compass is an angle called declination. Declination varies from place to place because the Earth’s magnetic field is not uniform it dips and undulates.

These local disturbances in the field can cause a compass needle to point away from both the geographic North Pole and the magnetic North Pole. According to the United States Geological Survey, at very high latitudes, a compass needle can even point south.

By using charts of declination or local calibrations, compass users can compensate for these differences and point themselves in the right direction.

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Like the earth itself, each magnet has a north and a south pole. If it can turn freely, the north pole of a magnet will turn towards the North Pole of the Earth. The south pole of a magnet will be attracted towards the South Pole of the Earth. Confusingly, the Earth’s North Pole actually has a south magnetic pole, which is why the north pole of a magnet is attracted to it. For the rule is that like poles repel each other (push each other away), while unlike poles attract.

The areas of a magnet that have magnetic strength are called “poles”. When you have more than one magnet, like (or same) poles repel, or push, each other. Opposite poles attract, or pull, each other. In other words, the north pole of one magnet will click together with the south pole of another magnet, and two north poles will push each other away. These acts of attraction and repulsion are called “magnetism, and the magnetic space around a magnet is called the “magnetic field.

Unless they came marked with “N” or “S,” the poles of a magnet look the same. One easy way to tell which pole is north and which is south is to set your magnet near a compass. The needle on the compass that normally points toward the North Pole of the Earth will move toward the magnet’s South Pole. This works because the needle in a compass is actually a magnet! So the north pole of the compasses’ needle magnet is attracted to the south pole of your magnet.

Another way to tell which is north and which is south is by dangling your magnet from a string. When you dangle a magnet, it automatically turns itself so that one pole is pointing directly north and the other directly south, which is why we call them the “north” and “southpoles.

Remember in the intro when we said all magnets have AT LEAST two poles? Well bar magnets have two poles, so their magnetic fields are called dipole which means–you guessed it–two poles! But some magnets have more than two poles. In fact, some have four, or six, or even eight! (These are called “octopoles”– doesn’t that sound like a cool Play Station™ game?) Some celestial objects, including stars and planets, have magnetic fields, and some of them have more than two poles! We call these fields “multipoles.” Earth is a good example of a dipole magnetic field–we have one North Pole and one South Pole (with a few weaker multipole parts, but let’s not get into that right now).

Picture Credit : Google


When an electric current runs through a wire, it creates a magnetic field. If the wire is wound round and round an iron core, the coil and core become strongly magnetized whenever the current is turned on. The coil of wire is called a solenoid.

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole, denoting the centre of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.

The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field.

Electromagnets are widely used as components of other electrical devices, such as motors, generators, electromechanical solenoids, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment. Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel.

Picture Credit : Google


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