Gravity is Optional - Magnets and Soda Cans

Gravity is Optional - EddyCurrents
Magnets and Soda Cans

Everyone knows that aluminum is not attracted to a magnet. We are taught that at an early age. These experiments use aluminum soda cans and magnets.

Whole can | Cutting the can | Pieces of the can | The bottom | Discussion

Whole can

Take an empty aluminum soda can. Tie a string to the pull tab (I use a slip loop) and bend the tab so that the can will spin without wobbling.

With the can suspended, move a magnet near the can and observe what happens. You should be able to make the can spin without touching it.

Now, hold the magnet near the can and observe how it stops the motion. This is one form of a magnetic brake. This is how some roller coasters are stopped. When they are wet, friction brakes tend to fail. When a train of people is moving at high speed, and things are a little wet, this is a serious safety issue. However, when the aluminum sheet on the bottom of a roller coaster moves at high speed between 2 magnets (or electromagnets), the car slows down. The faster the car is moving, the greater the stopping force.

This same type of magnetic brake is used on laboratory scales to stop oscillations.

You should also move the magnet toward the can. The quicker you move the magnet, the greater the effect (the greater the force). There is also an effect when you quickly move the magnet away from the can.

Cutting the can

The rest of the experiments on this page will require pieces of the can. Basically, you want to cut the bottom out of the can to make a spinner (sort of). Once the bottom is removed, you want to cut some flat pieces from the sides of the can.

It is possible to cut up an aluminum can with a pair of scissors. Careful, if you use your wife's scissors, you might not survive long enough to perform the experiments. Fortunately, I have my own scissors.

It is relatively dangerous to cut the can. I have been cut several times. It is difficult to start the first hole. Cutting is fairly easy (the metal is so thin) but the edges are extremely sharp. When removing the bottom, there are usually a number of extremely sharp points. As a result, I suggest wearing heavy leather work gloves.

Once the pieces are cut, be sure to smooth the edges and remove any sharp point that could draw blood. I normally use files and emery cloth for this.

Please be careful.

Pieces of the can

You will want several flat pieces cut from the side of the can. These should be a little larger than the size of your magnet. (Actually, you should experiment with different sizes.)

Place a magnet on top of the piece of metal. Now, quickly pick up the magnet. (Speed is important.)
Place the piece of aluminum on a smooth surface. Without touching the aluminum, quickly move the magnet over it. (Again, speed is important.)
Try both experiments with some coins of different sizes .. and any other metal you can find.

We have all been taught that aluminum is not attracted to a magnet. And it is well known that US coins are not affected by magnets. So, what is happening?

The bottom

If you have cut the can's bottom out "correctly", you can flip it upside down and and put the curved surface on a table. Make sure that only the center, and not the edge, touches the table. (Adjust and debur as necessary.)

There are 3 basic tricks.

Place the magnet in the center of the bottom and quickly lift the magnet. The aluminum (which is not magnetic) should jump off the table. (This is identical to the experiments above .. but still cool.)
Move the magnet around the outer edge of the bottom. The aluminum should start to spin. It is clear that the aluminum is attracted to the magnet.
When the aluminum disc is spinning, hold the magnet near the edge. This quickly stops the disc.

Of course, everyone thinks that moving the magnet causes a breeze and that the wind is spinning the bottom. So .. place the bottom on a sheet of cardboard (cut from the side of a cereal box), and move the magnet under the cardboard. This proves that air currents are not affecting the spinner.

Sometimes I use a clear sheet of plastic, or a sheet of glass, so that everyone can see the magnet.

Discussion

The order above shows the easiest experiments first. Of course, those were the last ones discovered.

I had been cutting up cans to try and make tubes. (This never worked.) When playing with some curved metal, I decided to see what might happen if I used a flat piece. I was able to drag these around with a magnet .. and to pick them up. Then I tried coins .. which also worked. Well, when I showed this to my juggling club, they were impressed.

The next week, Dave brought in the bottom of a can and a sheet of glass. He showed me how to spin it by placing it upside down and moving the magnet under the glass. Then I tried to pick it up using just the magnet. (It worked.) Then I used the magnet to stop the spinning disk.

I went home and started playing with whole cans suspended from a string. I tried several ways to attach the string, but my technique was worthless and the can wobbled quite a bit. Eventually, (about a month later) I realized that if I simply adjusted the tab, I could get rid of the wobble.

I think that the whole can and a copper tube make "better" demos, but they don't fit in my pocket. Instead, I sometimes carry a magnet, the bottom of a can, flat pieces of aluminum can, and a few aluminum rings.

Author: Robert Clemenzi