At the beginning of the video you see the grapes start to spin because of the air movement caused by my hand. But then the grapes spin back the other way when I bring a magnet near. The grapes continue to get pushed away from the magnet even when I flip the magnet around.
So what is happening?
Grapes are mostly water and water is diamagnetic. Diamagnetic means that it is repelled by magnets. This diamagnetic force is extremely weak, so we don’t normally notice it.
Actually all matter is diamagnetic. I know what you are thinking: lots of things are attracted to magnets, like my refrigerator. Your refrigerator is ferromagnetic, attracted to magnets. The diamagnetic force is so weak that it is overpowered by the ferromagnetic force.
Try this experiment so that you can see the diamagnetic force. It is fun and I found it hard to believe until I tried it.
1 very strong magnet
For the magnets, I used 10 Neodymium Magnets stacked together because the magnets that I normally have around my house were not strong enough.
Place a pin pointing straight up by sticking it through cardboard (or putting it in Play-Doh).
Cut a notch in the middle of a straw.
Stick a grape on each end of the straw. (I cut my straw to a point on each end to make it easier)
Set the straw on the needle so that the needle goes into the notch and touches the other side. Move the straw a little until it is balanced on the pin.
Cutting the notch in the straw allows the pin to touch the topside of the straw, and thus the fulcrum is above the center of mass. This makes it possible to keep the straw balanced.
Then bring the magnet near one of the grapes, but don’t touch it. The grapes should spin.
Have fun exploring diamagnetism, another amazing part of God’s creation.