Magnetic Cannon

Here’s a really cool experiment you can do at home, where you can build your own magnetically accelerated cannon! The balls don’t accelerate enough to actually hurt anyone, but you can see how dramatically fast they can go.

All you need are 9 ball bearings (we used 5/8 inch diameter) and two neodymium magnets, which you can find online. You need to be very careful with these magnets because they are quite strong.

The first thing you need to do is tape the magnets to the floor. We used space in between the tiles on a kitchen floor as our track. Start by taping one of the magnets down and sticking the balls to right side of the magnet.

Next, place the other magnet a few inches away and do the same. You should have 4-5 ball bearings attached to the magnets like in the picture below. You can experiment how the spacing between the magnets and number of balls affect the overall acceleration of the device.

To shoot the ball, just roll a single ball bearing along the tile line into the left side of the left magnet. You’ll create a chain reaction and a ball will go shooting off the right side of the right magnet!

How does it work?

This device is a great way to understand kinetic energy and potential energy. You can think of energy as an ability to do work. You should notice that your magnets attract the ball bearings with a pretty strong force. When you pull a ball bearing away, you are doing work to pull against this magnetic force.  So, when a ball bearing rolls towards a magnet, the magnet does work on the ball bearing and speeds it up. In this way, potential energy is being turned into kinetic energy.

When the ball hits the magnet, this energy is again transferred. Some is used up by making sound and a little heat. But, most travels through the magnet and stack of balls to the last ball. Because this last ball is pretty far from the magnet, it is weakly attached and leaves with almost the same speed as the first ball that hit the magnet on the left.

So, the green ball on the right leaves at a pretty fast speed and is accelerated by the second magnet to go even faster. Even more energy is transferred through the second phase releasing the last ball at a pretty incredible speed.

Adding more stages would theoretically increase the speed even more!


2 responses to “Magnetic Cannon

  1. What if you only have one ball on each side of the magnet do you get the same results? What if the balls are magnetic themselfs..What is the magnet is much stronger like have a pullforce of 500 lbs?.. I Really like this ..I think you gave the most detailed explanation i could find on the net.

  2. Thanks for your kind words! Putting just one ball on the other side will probably not work. The kinetic energy has to be transferred to a ball that is further from the magnet than the one hitting (that’s why we used 4 balls). A much stronger magnet has the potential to increase the kinetic energy transfer (faster ball). You should try it out!

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