Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.
|Goal:||Build a magnetic linear accelerator to launch a steel ball|
|Age:||Middle school and up|
|Safety Concerns:||Neodymium magnets are very strong and should be kept away from electronics. Wear safety goggles when launching your accelerator. Never launch a projectile near any people or animals. Use caution when cutting the tape with the precision knife.|
Imagine getting on a roller coaster. It's one of the fastest ones in the park and accelerates you up to 100 miles per hour! A little nervous, you look around and notice there's no enormous hill in front of you. How will you gather the momentum to reach such great speeds if you start from a flat surface? The answer is a magnetic linear accelerator.
Magnetic linear accelerators rely on the strength of opposing magnetic fields to propel objects forward at great speeds. In the case of this type of roller coaster, magnets on the ground and on the outside of the cars repel each other, causing the cars to zoom forward along the track. For a review on magnetic force before we begin, you can check out this lesson: Magnetic Force: Definition, Poles & Dipoles. Instead of using gravitational potential energy stored in the height of the first hill, these coasters use the force generated by magnets for their source of kinetic energy.
Today, we're going to build a model magnetic linear accelerator that will launch a small steel ball similarly to how roller coasters are launched around a track with this technology.
- Wooden ruler with a groove in the center
- 9 steel balls about 5/8'' in diameter
- 4 neodymium magnets that fit on the ruler, about one inch squared
- Safety goggles
- Precision knife
Safety Tip!! Keep neodymium magnets away from electronics and use caution when handling a precision knife.
1. Place one magnet about 2.5'' away from the end of the ruler directly over the groove in the center. Tape it into place and trim any excess tape from the edges with the precision knife.
2. Repeat step 1 with the next three magnets, placing each one 2.5'' away from the previous magnet.
3. Now, place two balls on the inside of each magnet in the ruler groove.
4. Put your safety goggles on.
Safety Tip!! Be careful when launching projectiles. Always aim projectiles in an open area away from people, pets, and breakable things.
5. Place the last steel ball in the groove of the ruler before the first magnet and hold it in place at the end of the ruler.
6. When you're ready to launch, let the first ball go.
Make sure you have measured the correct distance between your magnets. If the magnets are too close or too far away, there will be changes to the magnetic force that can affect the motion of the balls.
Why did the balls shoot forward when you launched the one you were holding?
How do you think adding more balls or magnets would affect the experiment?
Where did the energy needed to launch the balls come from?
How It Works
Magnetic linear accelerators rely on the magnetic force to create movement. When you pulled the first ball back to the beginning of the ruler, you used potential energy to keep it there. When you released the ball, its attraction to the magnet caused it to zoom forward and the potential energy was transferred to kinetic energy, or energy of movement. For a review of potential and kinetic energy, you can check out this lesson: Kinetic Energy to Potential Energy: Relationship in Different Energy Types.
The energy was transferred through the magnet to the first ball. But, the first ball is held closely to the magnet due to the magnetic force and only moved slightly. The second ball however, is farther away from the magnet so the kinetic energy is enough to overcome the magnetic force and allow it to move.
As it moves away eventually it enters the magnetic field of the second magnet, which pulls the ball towards itself with an even greater speed than the first magnet. To learn more about magnetic fields and how they affect motion, you can watch this lesson: What is a Magnetic Field?
This process repeats for each of the magnets on our linear accelerator until it reaches the ball at the end. Since there are no more magnets to block its path, the ball shoots out of the ruler. Adding more magnets, or larger magnets increasing the amount of magnetic force, and thus causes the balls to accelerate faster.
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