Extreme Science: Penny Shine

What you will need:

  • Two toothbrushes
    NOTE: DO NOT use your MOM AND DAD’S TOOTHBRUSHES for this experiment!
  • Adult supervision


  1. Take two toothbrushes and gently “wiggle” them as you press them together so that the bristles are all intertwined as shown.
  2. Now, attempt to pull the toothbrushes apart by pulling each handle in the direction shown below.
  3. You may find that this was a little harder than expected, yet not too difficult. Ask your Mom and Dad if they have any old toothbrushes that you can use for this experiment. Many times, parents will keep an old toothbrush around for cleaning tight areas. Make sure that it is clean, especially if they have used chemicals to clean with. Try the experiment again with old used toothbrushes. Did you find that was any difference?

What is going on?

In the original video that I watched online, the narrator implied that they were using two brand new, typical children’s toothbrushes. They went on to show that you could lift up to 35 pounds without the toothbrushes coming apart.

After trying this experiment for myself, I was amazed at the minimal effort that it took to pull the toothbrushes apart. I later saw this experiment done on another television show where they explained that the nylon bristles were actually rough when viewed under a microscope and that the “bumps” on one bristle fell into the “valleys” of the opposing bristle causing them to lock together due to friction.

Since I was not getting the same results, I purchased every different type of toothbrush I could find from soft to medium to hard bristle and from “whitening” to “plaque removing” specialty toothbrushes. Fortunately, every experiment ended the same way! You would think that this would have been disappointing but remember, you will always learn more when an experiment does NOT work the way you expect it to.

I looked up microscopic pictures of toothbrush bristles and found that, when they are new, they do in fact have a rough surface as well as a fairly sharp tip. I also found that as you use them, the tip will become rounded in shape and the surface will become fairly smooth.

I then built a platform that I could mount the toothbrushes on so that they were underneath an old paint mixer that I have in my garage and turned it on for more than two hours. Upon removing these two toothbrushes, I noticed that the bristles are no longer lined up parallel to each other as some of them were going in very different directions (kind of like your hair first thing in the morning) I again tried pressing the two toothbrushes together and found that when I attempted to pull them apart, it was VERY difficult!

YIPEE! It worked.

My conclusion is that it is not actually the surface of the nylon bristles that are “locking” together. Rather, it is the random directions of each individual bristle. This randomness will cause the bristles to now cross over each other so that when you apply pressure sideways, in an attempt to pull them apart, each bristle will apply pressure on the next creating the necessary friction to hold them together. I was able to easily lift a 30 pound weight with these two (brand new, very well used) toothbrushes.

Try this:

Try using different brushes such as scrub brushes and hand brooms to see how much force it will take to pull them apart.

Radical Rick

Extreme Science