Particle Physics Pinball

Particle Physics Pinball Exhibit Overview The particle physics pinball exhibit demonstrates the way particle accelerators investigate the structure of atoms. The goal is to be able to guess the mystery shape at the top of the pinball machine based on the way the pinballs bounce off the shape. Similarly, particle physicists at accelerators like the large hadron collider shoot electrons at atoms and measure the way those electrons scatter off them. Since we understand how electrons interact with different kinds of particles, we can infer what the atom is made of. In the demo, we can guess the shape and check if we are right, but of course physicists do not know the correct answer for atoms so instead they repeat the experiments many times until they have enough data to be confident in their answers.  Particle Physics Demo Guide There are typically a lot of museum visitors, especially children, who love to play with this demo, just having fun firing the ball bearings, but often with little understanding of how the demo relates to any particular physical concept. As a result, there are two modes I work in depending on their level of interest and attention span.   Game mode: In this mode I am just helping them see how the demo itself is a game to guess the shape at the top. I don’t start introducing anything related to particle physics yet. I recommend asking questions to gauge their understanding. 

• “What do you expect to happen when you fire the ball bearings toward the center of the shape”
• “What do you notice happens? Does it match what you expected?”
• “What if you fire it at an angle, from the center?” “How would it behave if the object were shaped differently for example a circle or a square”

If they seem to be engaged in these questions, you can start to ask them if they can guess what shape is present. You might ask:

• “Which shapes might be harder to distinguish, what might help you tell the difference” (You can show them then how to rotate the mystery shape)

Even if you stop here, this gets them thinking about the ideas even if you don’t get to the direct physical analogy. It’s better they have fun with the demo than get bored. Particle physics mode: If they continue to seem engaged in the game of guessing the shape you can start to introduce the connection to particle physics. Ask:

• “Can you guess what we might study with a method like this in physics?” 

Most visitors won’t know, but I often just use it as a way to see if they would want to know the answer.  They you can start to explain pieces of the analogy. You can introduce these in any way that seems appropriate. For example, tell them the ball bearings are like electrons that we used to study atoms. and tell them that just like they are learning about the mystery shape with ball bearings physicists can learn about atoms using electrons.  Particle Physics Analogy Descriptions Ball bearings=electrons: they are particles we understand well. We know how they interact with other things and therefore what we expect them to do in different situations Mystery shape= atoms: objects we want to understand better. We are trying to figure out what they are made of based on how the electrons bounce off them.  Ball bearing gun= particle accelerator: these are large machines that let us get electrons up to really high speeds and shoot them at atoms. We can then use precise sensors in these machines to track what the electrons do after they hit the atoms, in the same way you are watching what the ball bearings do. Fixing the demo:  This demo breaks a lot, but it is pretty simple to fix. The main issue is that visitors will start to fire the ball bearings before the machine has finished changing the shape and the balls get stuck at the bottom of the machine. So, the first thing I do is find the screwdriver that is usually on top of the pully demo, and straighten out the shape so that it’s level with the rest of the demo. Then, you can take the lock (it’s never actually locked) off the cover at the bottom and start taking the ball bearings out. It’s a bit of a slow process and you can only really do it one by one. Sometimes, you can get kids excited by asking them to help you fix the machine and their tiny fingers are often better at getting those balls out. Once you have them all you can put them back in through the hole above the shape.

Julia Sheffler, 2022-23 Wonders of Physics Outreach Fellow