Gauss Rifle, Film Can Cannon, and Levitation
The Gauss Rifle:
A Magnetic Linear Accelerator
This very simple toy uses a magnetic chain reaction to launch a steel marble at a target at high speed. The toy is very simple to build, going together in minutes, and is very simple to understand and explain, and yet fascinating to watch and to use.
Click on image for animated view
The photo above shows six frames of video showing the gauss rifle in action. Each frame shows 1/30th of a second. In the first frame, a steel ball starts rolling towards a magnet taped to a wooden ruler. In the second frame, a second ball can be seen speeding between the rightmost two magnets. By the third frame, the accelerator has sped up so much that the ball that is seen leaving the left side of the device is just a blur as it smashes into the target. One ball, starting at rest, has caused another ball to leave the device at a very high speed.
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on image for larger view
The materials are simple. We need a wooden ruler that has a groove in the top in which a steel ball can roll easily. Any piece of wood or aluminum or brass with a groove will work. We chose the ruler because they are easy to find around the house or at school or at a local stationery store.
We need some sticky tape. Again, almost any kind will do. Here we use Scotch brand transparent tape, but vinyl electrical tape works just as well.
We need four magnets. Most any type will do, but the stronger the magnets are, the faster the balls will go. Here we use the super strong gold-plated neodymium-iron-boron magnets we have made available in our catalog for the other projects. They work great.
We will also need nine steel balls, with a diameter that is a close match to the height of the magnets. We use 5/8 inch diameter nickel plated steel balls from our catalog.
The only tool we will need is a sharp knife for trimming the tape.
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We start by taping the first magnet to the ruler at the 2.5 inch mark. The distance is somewhat arbitrary -- we wanted to get all four magnets on a one foot ruler. Feel free to experiment with the spacing later.
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With the sharp knife, trim off any excess tape. Be careful, since the knife will be strongly attracted to the magnet.
It is very important that you keep the magnets from jumping together. They are made of a brittle sintered material that shatters like a ceramic. Tape the ruler to the table temporarily, so that it doesn't jump up to the next magnet as you tape the second magnet to the ruler.
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Continue taping the magnets to the ruler, leaving 2.5 inches between the magnets.
When all four magnets are taped to the ruler, it is time to load the gauss rifle with the balls.
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To the right of each magnet, place two steel balls. Arrange a target to the right of the device, so the ball does not roll down the street and get lost.
To fire the gauss rifle, set a steel ball in the groove to the left of the leftmost magnet. Let the ball go. If it is close enough to the magnet, it will start rolling by itself, and hit the magnet.
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When the gauss rifle fires, it will happen too fast to see. The ball on the right will shoot away from the gun, and hit the target with considerable force. Our one foot long version is designed so the speed is not enough to hurt someone, and you can use your hand or foot as a target.
For a complete explanation of the science behind the toy, and exactly how it works, see the full article at Scitoys.com.
Levitating pyrolytic graphite
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A diamagnet is a substance that acts like a mirror for magnetism. A bar magnet next to such a material sees a reflection of itself, and pushes away from the similar poles in the mirror.
The most diamagnetic substance known (at room temperature) is called pyrolytic graphite.
Pyrolytic graphite is a synthetic material, made by a process called chemical vapor deposition.
To make pyrolytic graphite, methane gas at low pressure (about 1 Torr) is heated to 2000 degrees Celsius. Very slowly, (one thousandth of an inch per hour) a layer of graphite grows.
The graphite made this way is very highly ordered, and the layers of carbon atoms form like a crystal of hexagonal sheets. These sheets lie on top of one another like sheets of mica. You can separate the layers with a sharp knife to make thinner sheets.
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Because the density of pyrolytic graphite is low, (the specific gravity is 2.1), it is light enough to be levitated above a sufficiently powerful magnet. A thick piece will still be too heavy, since the material above about a half of a millimeter does not contribute much to the lift. But if the piece is thin enough, it will simply slide right off of a strong magnet, and refuse to sit still on it.
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With a piece half a millimeter thick, using neodymium-iron-boron supermagnets, you can see from the photos that the piece is levitating about a millimeter above the magnets.
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To make the pyrolytic graphite plate sit still above the magnet, we need a way to force it towards the center.
We can do that by using four magnets. The poles of the magnets push on the diamagnetic material more strongly than other parts of the magnet. With four magnets, the four edges of the square of pyrolytic graphite will be pushed away from the four poles. If the square is slightly smaller than half the width of the four magnets (a little smaller than one magnet), then we can place it in the center, and it will be pushed to the middle and stay.
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Since diamagnetic materials are repelled by either pole, we can place the magnets with alternating north and south poles, and they will stick nicely to one another. I like to sit the whole array on a piece of sheet steel, so the magnets stay put.
The pyrolytic graphite plate floats above the magnets and springs back when you push it down with a finger.
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Pyrolytic graphite is not easy to find. The local hardware store won't be carrying it any time soon. But we carry it in our catalog, in pieces just the right size for the levitation project.
For more information about how to make this toy, how it works, why it works, and the science behind the toy, see the full article at Scitoys.com.
The Film Can Cannon
This toy was an instant favorite from the moment its first loud Bang! and flash of orange flame launched the little black film can up to bounce off our 26 foot ceiling.
It has several names: the Piezo-Popper, the Binaca Bomb, the Photo-Flash -- you will probably come up with more.
The toy is very easy to make, going together in about 15 minutes, at a cost of two or three dollars if all the parts are purchased new, or free if you don't throw away certain common household items.
The fuel for the cannon can be found around the house. We have run ours on perfume, hair spray, and (our favorite) Wintergreen Binaca mouth freshener.
The cannon is very simple. A pair of wires are pushed through a slit made in the top of a plastic 25 millimeter film can. The other end of the wires are soldered to the igniter element from an electronic cigarette or fireplace lighter. I chose to mount these elements on a block of wood, but this is optional if you're in a hurry.
To fire the cannon, you spray the fuel (one squirt of perfume or Binaca, or a very short squirt of hair spray) into the plastic film can, push the can down on the lid, and press the igniter.
With a loud Bang! and a flash of orange flame, the little can goes sailing into the air. With some practice in getting just the right amount of fuel in the can, it will go as high as 30 feet straight up. If too much or too little fuel is used, it will either not ignite at all, or it will not go very high.
For a complete explanation of the science behind the toy, and exactly how it works, along with detailed instructions for building your own, see the full article at Scitoys.com. You can order one in kit form from our catalog,