The SFK Project: #8 Electric WormFollow article
What you need:
- AAA battery
- 4 Neodym magnets, cylinder 15 mm diameter, 8 mm height (search google for “super magnet” store)
- 25 m copper wire not insulated, silver- or tin-plated, 1 mm (search, e.g. Amazon)
- 50 cm Copper tube, 22 mm diameter
- blunt table knife
- gaffer tape
- blue tack
- black and red waterproof marker
What you will get at the end:
A battery travelling through a wire coil
Words of warning:
An adult should always supervise these experiments. Please do not leave your children alone with strong Neodym magnets and knives. When strong magnets bang together, they can severely squeeze skin and fingers. It will be impossible for kids to separate two of those magnets when they cling together. Please read in SFK project #7 how you can use a blunt table knife to separate the magnets and to prevent them from clinging together.
How to build:
Please read SFK project #7 to find out how you can detect and mark the magnets north poles. In this experiment, we do need all 4 Neodym magnets marked with "N" at their north poles.
We need to make a nice and perfect coil out of the 25 m copper wire. The best way to do so is by using the copper tube and winding it on this tube tightly.
Once you have done about 5 cm of windings, you should use gaffer tape to fix the beginning to the tube. This makes it much easier to turn the pipe with one hand while guiding the wire onto the tube with the other hand. I’ve fixed the windings every 5 cm like this:
The better you do this job, the better the worm will travel. A sloppy coil like this will not correctly work:
The windings are not equal and upright but squeezed and with sharp bents in. Wind up like this to get the best results:
When removing the tape, my coil looked like this:
Let’s do the worm now. Make a small role of blue tack and place it on to of the AAA battery (marked with “+”):
Place a magnet with the “S” pointing down on top of the battery and press until the magnet contacts the battery’s + pole:
It is important not to get blue tack between the battery’s pole and the magnet surface. We need electrical contact between the two. Use the protruding blue tack to form a stabilising ring. We want the battery to stay stable on the pole and not to get in contact with the metal case of the battery:
Turn the battery round and place a second magnet on to of the pole marked “-“, the black “N” pointing away from the battery:
Take the third magnet and slowly let it cling to the magnet on the “-“ pole of the battery. Use the fourth magnet to cling it to the one on the “+” pole of the battery. Please let this do an adult!!! It is tough to make the magnets bump together slowly, and you risk squeezing your skin if the magnets get out of control.
Place the side with the blue tack (“+”) towards the entry of the coil:
You will feel a force when trying to enter the worm into the coil. The worm seems to hate the coil and wants to escape. Now turn it the other way round with the “-“ (no blue tack) into the coil. Suddenly the worm likes the coil so much that it dives in and rushes through to come out at the other end of the coil. Tape one end of the coil to the table. When you have inserted the worm, quickly attach the other end of the coil to the beginning so that you get a closed loop:
The worm gets hot while making his turns through the loop. There is a high current flowing through the battery and the magnets which is heating them. Please take care not to burn your fingers. Better let them cool down a while before touching them.
Because of the high current, the battery will not last for very long. So this will be an expensive toy if you play for hours using dozens of batteries.
How it works:
Do you know what happens if you send an electric current through a coil? The coil gets a magnet! That is what is called an electromagnet. The direction of the magnet (on which side of the coil is north) depends on the direction of the current:
When you placed the battery inside the coil, the magnets were making contact with the coil. You got a complete circuit of current (see FSK project #3 to get more explanation about that): Current is flowing out of the battery, into the magnets, into the wire of the coil, out of the wire into the other side’s magnets and back into the battery. This turns the coil into a magnet. And if the direction of the current is correct, the electromagnet is attracting the Neodym magnets, pulling them (together with the battery) inside the coil. When the direction is wrong, the electromagnet repels the Neodym magnets, and the worm does not like to creep into the coil.
Did you know that people are using a magnetic field to move a vehicle? That is called a magnetic levitation train. This one is from Shanghai, and its maximum speed is 431 km/h (268 mph):