There are two ways to create a magnetic field. First, you can wrap wire around a nail and attach the ends of the wire to a battery to make an electromagnet. When you connect the battery to the wires, current begins to flow, creating a magnetic field. However, the magnets that stick to your fridge are neither moving nor plugged into the electrical outlet – which leads to the second way to make a magnetic field: by rubbing a nail with a magnet to line up the electron spin. You can essential “choreograph” the way an electron spins around the atom to increase the magnetic field of the material. This project is for advanced students.

There are several different types of magnets. Permanent magnets are materials that stay magnetized, no matter what you do to it… even if you whack it on the floor (which you can do with a magnetized nail to demagnetize it). You can temporarily magnetize certain materials, such as iron, nickel, and cobalt. And an electromagnet is basically a magnet that you can switch on and off and reverse the north and south poles.

The strength of a magnetic field is measured in “Gauss”. The Earth’s magnetic field measures 0.5 Gauss. Typical refrigerator magnets are 50 Gauss. Neodymium magnets (like the ones we’re going to use in this project) measure at 2,000 Gauss. The largest magnetic fields have been found around distant magnetars (neutron stars with extremely powerful magnetic fields), measuring at 10,000,000,000,000,000 Gauss. (A neutron star is what’s left over from certain types of supernovae, and typically the size of Manhattan.)

Linear accelerators (also known as a linac) use different methods to move particles to very high speeds. One way is through induction, which is basically a pulsed electromagnet. We’re going to use a slow input speed and super-strong magnets and multiply the effect to generate a high-speed ball bearing to shoot across the floor.

For this experiment, you will need:
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• Wood or plastic ruler with a groove down the center
• Thick rubber bands or strong, super-sticky tape
• Four super-strong magnets (try 12mm or ½” neodymium magnets)
• Nine steel ball bearings (1/2”, 5/8”, or other sizes)

Here’s what you do:

Question: Does it really matter where where you start the first ball bearing? If so, does it matter much?

What’s going on? The metal ball bearing is seriously attracted to your magnets, and this pull intensifies the closer the ball gets to the magnet (inverse-square law). When the ball smacks into the magnet, the energy wave from the impact zips through the magnet and attached ball bearings until it knocks the furthest ball free, which has the least magnetic pull on it (it’s furthest from the magnet)… which is good, or it would be slowed down and possible reattached to the magnet it just broke away from.

With each impact, there’s an increase in velocity. Imagine if you had a hundred of these things lined up… how fast could you get that last ball bearing going?

After each firing, you have to reset your system, and chances are, it takes a bit of effort to pull the ball bearings from the magnets! you are providing the energy that gets released during each collision and adds to the velocity of the ball bearings.

Want to turn this into a Science Fair Project?

Exercises

1.  Does it really matter where you start the first ball bearing? If so, does it matter much?
2.  Why does only the last ball go flying away? Why don’t the others break away as well?
3.  What happens if you try this experiment without the magnets?
4.   How many inches did the first initial ball (the one you let go of) travel?
5.   How many inches did the last ball (the one that detached from the magnet) travel?
6.   Why did we use four magnets in the second lab? What did that do?

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### 4 Responses to “Linear Accelerator”

1. Kaelen Davis says:

Thanks!

2. Kaelen Davis says:

It looks pretty interesting. Did you do it? I don’t have the subscription that allows me to see this video. How does it work?

3. Lydia Fancher says:

wow that is so cool!!!

Cameron, age 13