Accelerators

Physics, Engineering:	Acceleration, Accelerators
Grade Range:	Middle School, High School
Format:	Hands-on, Stage

This demonstration is intended for an advanced group of students, so be prepared for questions on the topic. The setup for this demonstration can be touchy, and if bumped the marbles might fire on their own!

Materials

• Neodynium Magnets
• Accelerator Rail
• Large & Small Metal Marbles
• Slingshots with Ping Pong Balls
• Target

Safety Precautions

Please read the Physical Demonstration section of the Demonstration Safety page before performing this demonstration.

Demonstration

Preparation

Set up the accelerator rail: Place the magnets in their marked spots underneath the rail, and lock them in place by putting a large marble on the other side of the rail. On the front side of each large marble, place a series of small metal marbles until the last one in the series is only barely attracted to the one beside it. For the last series, place the smallest marble on the end. Place a target just past the rail to catch the last marble when it is launched.

Presentation

1. Ask the students to give examples of acceleration. Explain that acceleration is an increasing velocity over time.
2. Take out the slingshot, and explain that the ball is accelerated until the rubber band is no longer pushing it away. Ask the students if they can think of a way to accelerate the ball even more after you launch it, without slowing it down. After taking ideas, explain that this is how a particle accelerator works, such as FRIB or the NSCL.
3. Show the magnet accelerator setup, and use a medium sized metal marble to activate the chain reaction. When you roll the marble into the first series, they will all fire the last marbles in their chains, and the last marble fired will be moving really fast!

Why This Works

Velocity is when something is moving at a fixed speed, like a car going 25 mph. Acceleration is when something has an increase in velocity over a period of time. Acceleration is when something is "speeding up", like a car going from 25 mph to 45 mph in a few seconds. An Accelerator is a device or machine that can accelerate something. In a vehicle, the accelerator in a car is able to speed up the vehicle so you can drive at the speed limit. The car's accelerator is powered by the energy released from the fuel used. However, we can experience acceleration in other ways as well, such as the downward acceleration of gravity or acceleration from the pull or push between magnetic materials.

The setup we have can helps us visualize one way how a Particle Accelerator, a machine that can make atomic particles move extremely fast, can work. To accelerate a particle, such as an atom, the particle will first be stripped of any electrons on it, so that it is a positive ion. The accelerator will release it towards a negatively charged ring, which it accelerates towards. The moment the particle reaches the center of the ring, the charge will “flip”, meaning that the positive and negative sides of the ring will switch. This send the particle flying through it, and it will get a second increase in the acceleration from the push of the positive charge. By controlling the rate that the charges flip, we can get a particle moving extremely fast, even up to half the speed of light! You can think of the initial acceleration as being like the ball being fired by the slingshot. The "flip" would be if we could fire the ball, and then have a second slingshot fire it in the same direction as the ball gets to it.

The setup works by simulating the “flip” with the distance between the ends of the marble series. The last marble in each series is only barely held on, so it will be flung off by the collision of the “particle” marble with the first one in the chain. The last marble will then have the speed of the original particle marble, and will then speed up as it approaches the next magnetic marble. When it collides with the next chain it will pass on the speed increase (including that gained from accelerating towards the next magnet) to the next marble released, and so on. After repeating this process, we can see that the last marble on the end chain flies off much faster than the first marble due to this acceleration process.

Additional Information

• The magnetic accelerator setup is similar to how a MagLev train works. The train is suspended above the rail by electromagnets, and by having a strong magnetic charge in front of the train, it will accelerate towards it.
• This demonstration is a part of the Nuclear Physics Show