Knock Over a Coin Without Touching It—And Make Aluminum Foil Float!? Have Fun with Eddy Current Experiments at Home! (Faraday Desk)
I am Ken Kuwako, your Science Trainer. Every day is an experiment!
“I wish I could move objects without touching them, just like a superpower…” Believe it or not, you can make that wish come true right now using the power of science! Watch as aluminum foil—which shouldn’t react to magnets—floats into the air, or a high-speed spinning top stops dead as if it hit an invisible wall. Behind these wonders lies the work of Eddy Currents, a phenomenon that acts almost like a transparent ghost of electricity. Today, I will introduce several experiments where you can experience this mysterious “invisible force” using everyday items.
Moving Coins Without Touching Them
Let’s start with an experiment that looks like a magic trick. All you need are coins made of aluminum or copper (like a Japanese 1-yen or 10-yen coin) and a strong magnet. Normally, aluminum and copper are not attracted to magnets. However, try bringing the magnet close to the coin and then pulling it away suddenly. The coin will tip over as if it is being pulled by the magnet! Why does metal move when it isn’t supposed to react to magnetism at all?
Stopping Pot Lids, Fidget Spinners, and Gyroscopes Without Touching Them
Next, let’s try stopping a rotating object using a non-contact method. Spin a pot lid on a table and bring a magnet close to it… the rotation stops instantly, just like hitting the brakes.
Similarly, you can stop a fast-spinning fidget spinner without touching it. It is also quite a sight to line up several precision gyroscopes (Chikyu-goma) and stop them all at once with a magnet.
These phenomena occur because Eddy Currents generated within the metal create a magnetic force that opposes the direction of rotation.
The Magic of IH: Levitating Aluminum Foil
The IH (Induction Heating) cooktop in your kitchen is actually a powerhouse of Eddy Currents. If you place a piece of aluminum foil on an IH stove and turn it on… the foil will suddenly float up into the air!
When you flip the switch…
It floats perfectly! No tricks were used on the foil. The coils inside the IH cooktop change the magnetic field rapidly, which induces strong Eddy Currents in the foil. This creates a repulsive force—similar to two magnets pushing apart—causing it to levitate. The reason it floats up and down periodically is likely due to the IH’s safety sensor, which cuts and restores the current when it senses that a “pot” is missing.
Dropping a Magnet Through an Aluminum Pipe
Finally, let’s look at an experiment that makes you question the laws of gravity. Try dropping a magnet through an aluminum pipe.
If you drop the magnet outside the pipe, it falls instantly. But when you drop it inside the pipe, it falls slowly, as if it were in slow motion!
As the magnet moves through the pipe, Eddy Currents are generated on the pipe’s walls, creating a magnetic field that opposes and slows down the magnet’s fall. The stronger the Neodymium magnet you use, the stronger this “brake” becomes, and the longer it takes to fall.
What Exactly Are Eddy Currents?
Let’s take a closer look at the secret behind these strange forces: the Eddy Current Brake. This is a highly reliable technology used in the braking systems of Shinkansen bullet trains, heavy trucks, and roller coasters.
Eddy Currents are loops of electrical current induced within a conductor by a changing magnetic field. When you move a magnet near a metal plate, the metal tries to “cancel out” the change in magnetism, causing electricity to swirl inside like a whirlpool.
As shown in the diagram below, when a magnet slides over a metal plate, the area in front of the moving magnet tries to push it away, while the area behind tries to pull it back.
By using this principle, it is even possible to stop a violently vibrating coil instantly.
This story goes back to 1831, when Michael Faraday discovered Electromagnetic Induction. He invented the “Faraday Disk,” which extracted a continuous current from magnetism. By rotating a copper disk between the poles of a U-shaped magnet, a current is generated. This is the root of modern power generators! You can even experience this mechanism firsthand at the National Museum of Nature and Science in Tokyo.
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