Abstract

Objective

Introduction

Have you ever played with magnets, sticking them together and pulling them apart? Maybe you have seen how magnets attract paper clips and pins? Have you ever felt that tug when you tried to remove something from the magnet? If you have, then you have experienced the effects of magnetic fields. A magnetic field is a force that comes from a magnet, and it is either attractive (meaning it attracts) or repulsive (meaning it repels). A magnetic field is a force, just like gravity, and it can have magnitude and direction.

You might be thinking, "Great, magnets have magnetic fields, so what?" What kinds of things can I do with magnets, other than just sticking them to stuff?" Well, it turns out that magnetic fields are used in all kinds of things, like circuits and motors, compasses, and MRI equipment. In this physics science project, you will see a magnetic field at work and use it to make a neat toy called a Gauss rifle. Don't worry, this is not a rifle that is used to shoot things, but to demonstrate physics principles like magnetism, and others that are discussed below.

A Gauss rifle is made up of at least one magnet stage, but could have several magnet stages next to each other. A magnet stage is a magnet with several ball bearings next to it on one side. The first magnet stage in this science project will have one ball bearing on the other side of it. To get the Gauss rifle to shoot a ball bearing, the first ball bearing rolls toward the first magnet stage and then hits the first magnet. This starts a chain reaction that ends with the last ball bearing being ejected from the gun. Watch the video below to see a Gauss gun in action.

So how does a Gauss rifle work? When you give the first ball a slight nudge, it moves forward. As it gets closer to the neodymium magnet, the magnetic field from the magnet pulls the ball toward the magnet. The ball bearing accelerates towards the magnet due to the magnetic field. When the ball bearing hits the magnet, it transfers the energy that it got while rolling the distance through the magnetic field to the first magnet. When the ball transfers energy to the magnet, it has done work on the magnet. The magnet now has energy, mass and velocity. What is going to happen to the magnet's velocity? The magnet is going to hit the ball bearing next to it and transfer the velocity to the ball bearing. This concept is called conservation of momentum. The ball bearing then hits the ball bearing next to it and momentum keeps getting transferred until the last ball bearing shoots off. In a gun where there is more than one magnet stage, this last ball bearing is attracted to the second magnet because of that magnet's magnetic field, so the ball bearing accelerates toward the second magnet and the process starts again. The only difference is that the energy that the ball bearing from the previous magnet stage gives to the second magnet is higher than the energy of the ball bearing that started the chain reaction.

So how fast is the final ball bearing that shoots off going? What is its velocity? How far will it go? In this physics science project, you will answer these questions and look at the velocity of the final ball bearing, dependent on the number of magnet stages. The distance that the ball travels will depend on how fast the ball was going when it was shot, as well as on gravity— the force that attracts everything on Earth— which will eventually pull the ball down. The Gauss rifle is not only a great toy for demonstration, but you will also gain a whole lot of physics knowledge from it.

Terms, Concepts, and Questions to Start Background Research

• Magnetic field
• Force
• Magnitude
• Acceleration
• Energy
• Work
• Mass
• Velocity
• Conservation of momentum
• Gravity
• Data
• Square root
• Trajectory

Questions

• What is a magnet and what are some magnetic materials?
• What is the difference between velocity and acceleration?
• What is conservation of momentum and what are Newton's laws of motion?

Bibliography

• KidsLoveKits.com (n.d.). The Gauss Rifle: A Magnetic Linear Accelerator. Retrieved October 7, 2010, from http://www.kidslovekits.com/projects/Gauss_Rifle/index.html

These next three sources go into more detail about the physics of horizontally launched projectiles and the motion equations.

• The Physics Classroom. (2010). Horizontally Launched Projectile. Retrieved October 7, 2010, from http://www.physicsclassroom.com/mmedia/vectors/hlp.cfm
• Wikipedia Contributors. (2010, August 27). Trajectory of a Projectile. Wikipedia: The Online Encyclopedia. Retrieved October 7, 2010, from http://en.wikipedia.org/w/index.php?title=Trajectory_of_a_projectile&oldid=381221925
• HyperPhysics. (n.d.). Trajectories. Retrieved October 7, 2010, from http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html

Materials and Equipment

• Gauss rifle, magnetic linear accelerator standard kit (2). You can order the kits from www.miniscience.com, part number GRIFLE. The kit comes with four neodymium magnets that are ½ inch in diameter and ½ inch thick, ten ½-inch nickel-plated steel balls, and two wood dowels.
• Elmer's® Carpenter's Wood Glue
• Clear tape
• Scissors or box knife
• Plastic box, approximately the size of a shoe box
• Sand, 2 cups
• Tape measure (metric)
• Table in front of which there is ample room and will not be a lot of foot traffic
• Calculator with square root function
• Lab notebook

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Experimental Procedure

Building the Slide for the Rifle

1. Open the first kit and take out the wood dowels. You are going to make a slide on which the magnets and balls will sit on and move down.
2. Place the dowels evenly next to each other and make sure the ends are flush (lined up). Tape the ends together with clear tape. The tape will temporarily hold them together.
3. Place the taped dowels on the table and then carefully glue them together with wood glue. Try to prevent the glue from leaking through to the other side.
4. Let the glue dry and then take the pieces of tape off.

Setting Up the Experiment

1. Place the wood slide on the table and put a neodymium magnet on the slide, toward one end. Place two ball bearings on one side of the magnet such that the last ball is at the end of slide. See Figure 1. This step is represented by the magnet and ball bearings on the right side of the figure.

Figure 1. Image of a one-magnet stage Gauss rifle. (Courtesy of Wen Phan and Luke Agajanian, 2010.)

2. Now wrap a piece of tape around the magnet so that the ends of the tape are slightly wrapped around the wood slide. Remove the ball bearings. Use the scissors or box knife to cut off the excess tape.
3. Place the wood slide on the table so that the end of the slide is flush with the end of the table.
4. Place two ball bearings on one side of the magnet at the end of the slide (where they were located in step 1).
5. Pour the sand in the plastic box and smooth it out so that the sand is approximately level. Place the box on the floor a couple of feet away from the edge of the table.
6. Place one ball bearing on the other side of the magnet, about 1 inch away.
7. Measure the height of the table upon which the Gauss rifle is sitting. Record this value in your lab notebook.

Shooting the One Magnet Stage Gauss Rifle

1. Practice shooting the Gauss rifle so that you can place the plastic box at the correct distance for accurate measurements, as follows. Your experiment will look something like Figure 1.
2. Lift the slide just a little to get the ball rolling toward the magnet. Keep an eye on the last ball and where it lands so that you know where to place the plastic box. Caution: Be sure there is nothing breakable and nobody in front of the setup before you begin testing.
3. Place the box so that the ball will land approximately in the middle of the plastic box.
4. Now make a table, like the one below, in your lab notebook so that you can record the data that you get from your experiments.

5. Replace the correct number of balls on either side of the magnet.
6. Now lift the slide just a little to get the ball rolling toward the magnet. After the ball lands, take the tape measure and measure the horizontal distance from the edge of the table to the spot where the ball landed in the box. Record this distance value in the data table in your lab notebook.
7. Retrieve the ball from the box, smooth the sand, and replace the ball in its original position on the slide.
8. Repeat steps 6–7 two more times for a total of three trials. It is a good idea to repeat your experiments to make sure that your data is reproducible and accurate.

Shooting a Multiple Stage Gauss Rifle

1. You now have data for a one-magnet stage Gauss rifle. But what happens when you have more that one magnet stage?
2. Build a two-magnet stage Gauss rifle. Add a second stage that is 4 inches (in.) down the slide from the first stage. Remove the ball bearings from the rifle. Place the second magnet 4 in. down from the first magnet and tape it down to the wood slide. Cut off any excess tape.
3. Now place two ball bearings, each to one side of each magnet and one ball to the other side of the second magnet. See Figure 2 to see how to arrange the magnets and balls.

Figure 2. Drawing of a multi-magnet stage Gauss rifle. (Courtesy of Wen Phan and Luke Agajanian, 2010.)

4. Practice shooting the Gauss rifle so that you can place the plastic box at the correct distance for accurate measurements.
5. Lift the slide just a little to get the ball rolling toward the magnet. Keep an eye on the last ball and where it lands so that you know where to place the plastic box.
6. Place the box so that the ball will land approximately in the middle of the box.
7. After your practice, lift the slide a tiny amount to get the ball rolling towards the magnet. After the last ball lands, take the tape measure and measure the horizontal distance from the edge of the table to the spot where the ball landed in the box. Record this distance value in the data table in your lab notebook.
8. Retrieve the ball from the box, smooth the sand and replace the ball in its original position on the slide.
9. Repeat steps 7–8 two more times for a total of three trials. It is important to repeat your experiments to make sure that your data is reproducible and accurate.
10. Repeat steps 2–9 for a three-magnet stage Gauss rifle. Remember to record all data in your data table in your lab notebook.
11. Repeat steps 2–9 for a four-magnet stage Gauss rifle. Remember to record all data in your data table in your lab notebook.

Analyzing the Data

1. Now review the data that you got in the previous two sections.
2. Create a plot of the distance dependent upon the number of magnet stages. Label the x-axis Magnet Stages and the y-axis Distance.
3. Now calculate the velocity at which the ball was ejected from the wood slide (the Gauss rifle). To do this calculation, use Equation 1. Record your results in a table, like the one shown below.

Equation 1:

4. Average the data from the table above. Average the velocity for each magnet stage (1, 2, 3, or 4) over the three trials. Record your data in a table like the one shown below.

4. Now make a plot of the average velocity dependent upon the number of magnet stages. Label the x-axis Magnet Stages and the y-axis Average Velocity.
5. What do the plots that you made tell you? How is velocity affected by the increase in magnet stages?

Variations

• Purchase a second Gauss rifle kit and incrementally increase the number of magnet stages until you get to eight magnet stages. Does the velocity increase or decrease with the increase in magnet stages?
• Try increasing the distance between magnet stages. How does this affect velocity?
• Equation 1 does not account for the effect of air resistance. How do you think air resistance affects the distance and trajectory that the ball bearing will travel? Check out the references listed in the Bibliography for more information on how to derive equation 1.

• For more science project ideas in this area of science, see Physics Project Ideas.

Credits

Michelle Maranowski, PhD, Science Buddies

This science project is based upon the following Science Buddies Clever Scientist Award winning project: Agajanian, L. (2010). Gauss Rifle Magnetic Linear Accelerator.

Last edit date: 2012-02-14 11:00:00