Category Archives: Physics

Magnetic Raisins

The common phenomenon of magnetism is familiar to most of us as the result of playing with magnets to pick up paper clips and nails. That strong effect goes by the name of ferromagnetism. There are two other types of magnetism unknown to most people. They are paramagnetism and diamagnetism. These two types are much weaker than ferromagnetism and go unseen. But, they exist and are observable under the right circumstances.

To demonstrate diamagnetism, I suspended dried raisins on the ends of a wooden skewer which was hanging by a fine thread. The assembly is very sensitive to twisting forces. I brought a very strong neodymium magnet close to the raisin at one end. Watch what happened.

The same effect occurred if the magnet was reversed. The raisin always repelled weakly. You might wonder if other things exhibit diamagnetism. What about a grape? This link takes you to a video by the Exploratorium in San Francisco. He tests a grape and even aluminum foil. The results might surprise you.

Water is a substance that exhibits diamagnetism. Objects consisting of nearly all water can be seen to repel from strong magnets. Scientists have even tested the effect on a living tiny frog. They were able to levitate the frog in a strong magnetic field. It suffered no ill effects.

If you are more curious and would like to see some explanation of these magnetic effects, watch this video from Khan Academy.


Gravity | Silly Science Trick

In case you have nothing else to do today…

How I See It

Put a nickel on top of a quarter. Or, use whatever coins you have with the top one smaller than the bottom one. Hold them above your other hand. Drop them. They will rotate and reverse places. Get the distance just right and they will land softly in your lower hand. Great party trick. 🙂

I used my Samsung Galaxy s5 to film this at 1/8 speed. YouTube allowed me to trim out some dead time and shorten the video. It also did some minor enhancements to lighting and color.

After a year of using the phone, it was time to try some unused features. I am not an avid phone user.

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Fresnel Lenses | How They Work

How I See It

In a recent post about Maine lighthouses, I included two photos of the Fresnel lenses used to project the bright light beam across the water. One of the readers is a man I’ve enjoyed working with before in the blog world. He suggested I add a post with some description of how the Fresnel lens works. Here it is.

Basics of Converging Lenses

The converging, or convex lens, is able to bring parallel rays of light toward a focal point. As a child, I played with a magnifying glass lens to burn leaves, grass, and other things.


The lens can also be used in a different way to project light rays parallel to each other in a beam. Simple projectors work on this basic principle. A lighthouse is designed to do this.

ConvergeLens2Large Lens Applications

A problem arises when the optical instrument using a convex lens becomes very large. The…

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