Five DIY physics demos

In March 2020, Ketevan Akhobadze, an exhibit developer for the Lederman Science Center, turned off the power and watched the mist disappear from the center’s cloud chamber—a simple particle detector used to teach visitors about cosmic rays.

Normally, the science center—located at the US Department of Energy’s Fermi National Accelerator Laboratory—is filled with school groups and families exploring the laws of physics through interactive exhibits. But due to the coronavirus pandemic, the center is temporarily closed. Over the past year, Fermilab’s Education and Public Engagement (EPE) Office has continued to bring Fermilab science to the public by taking many of its programs virtual. 

Luckily, Akhobadze has a knack for creating in seclusion. “I was an only child,” she says, “and my grandma would watch me while both my parents were at work. I had a lot of time for myself, and I would spend it in our large garden exploring and building.”

Akhobadze picked the habit back up again while working for the EPE Office from home. With the help of her teenage daughter, Ellen, and under the watchful eye of their dog, Brownie, she created several DIY physics activities, virtual exhibits and short videos. 

Now, she wants to continue with the other part of her job: sharing her projects with anyone who wants to learn. Fermilab EPE regularly features videos of exhibits on social media, and here, Akhobadze shares how to create a selection of those exhibits at home.

Akhobadze recommends that DIY activities be conducted under adult supervision.

DIY particle accelerator

Don’t have space for a Large Hadron Collider at home? This simple exhibit shows how an accelerator works without the need of a 17-mile underground ring.

Many particle accelerators push subatomic projectiles, such as protons, with standing radio waves, waves whose peaks and troughs stay in the same position as their electric and magnetic fields oscillate up and down and sideways. The charged particles interact with the waves and ride the peaks of their electric fields to gain momentum. 

In this activity, swinging pendulums represent the standing radio waves, and ping-pong balls represent the accelerating particles.

Goal:

Create a ping-pong-ball accelerator by using two swinging pendulums to push a ball along a track.

Materials:

• 2 rubber balls
• at least 1 ping-pong ball
• spool of string
• 3 wooden rods ~6.5 ft (2 m) long and ~0.5 in (1-2 cm) thick

Set-up:

• Secure a wooden rod ~2 ft (60 cm) above a long and flat surface.
• Tie or glue 2.5 ft (~80 cm) of string to each of the rubber balls to make two long pendulums.
• Attach the pendulums to the elevated wooden rod so that they are ~1.5 ft (40 centimeters) apart and hang 0.5 in (~1 cm) from the ground.
• With the two remaining wooden rods, create a track that is directly below and parallel to the elevated support rod. The pendulums will push the ping-pong ball along this track.

Try this:

• The two pendulums should push the ping-pong ball in tandem: That is, the first pendulum passes the ping-pong ball to the second, which then pushes it again in the same direction. What happens if your timing is off?
• Play with the speed and amplitude of the pendulums. How does increasing or decreasing their starting height affect the momentum of the ping pong ball? How does it affect the timing of the pendulums?

Pro move:

The linear accelerator at the start of Fermilab’s accelerator complex uses several accelerating cavities in a row. How many accelerating pendulums can you add to your ping-pong ball accelerator?

Warp spacetime

Gravity got you down? Turns out stars and planets feel the same! This demo shows the relationship between mass, gravity and the curvature of spacetime.

In 1916, Albert Einstein revolutionized physics when he proposed the general theory of relativity: the theory that spacetime behaves like a flexible fabric that is stretched and deformed by massive objects. Curvatures in spacetime determine the strength of the pull of gravity near an object, something we can see in the universe as both light and the orbits of planets bend around massive stars. 

Goal:

Simulate the general theory of relativity by building a miniature universe with flexible spacetime.

Materials:

• 1 yard of stretchy fabric (such as Lycra)
• 1 large, open-top box (cardboard or wood)
• 1 stapler
• 2–3 weights of varying sizes
• 10–15 marbles or ball bearings

Set-up:

• Stretch the fabric over the top of the open box.
• Staple it on the sides. (It should form a suspended and taut surface.)

Try this:

• Place a weight onto the fabric. What happens? The stretched fabric represents spacetime, and each weight represents a massive body such as a star or galaxy cluster. 
• Roll a marble or ball bearing past the massive object. What happens to its trajectory?
• Play with the speed of the projectile and size of the weight. Can you get the projectile to orbit the mass?

Pro move:

With safety pins, hang a mass underneath the spacetime. Can you guess the size of the mass based on the trajectory of the projectiles?

This is how physicists measure the amount dark matter in the universe. Dark matter is plentiful and warps spacetime but has so far evaded other forms of detection.

Mapping shape with particle scattering

Can’t find your microscope? No need! This exhibit shows how scientists can determine the shape and structure of microscopic objects by scattering subatomic particles off of them.

In the early 1900s, a team of physicists lead by Ernest Rutherford fired alpha particles at a thin leaf of gold foil. Most of the particles passed straight through, but a few rebounded in odd directions. This experiment led to the discovery of the atomic nucleus, the part of the gold atoms that sent the alpha particles ricocheting away. 

Since then, scientists and engineers have used particle scattering to determine the microscopic structures of everything from proteins to tractor parts.

Goal:

Determine the shape of a hidden object by studying how ball bearings bounce off of it.

Materials:

• 6 mm steel bearing balls
• small objects (such as a saucer, a cellphone, a pen, etc.)
• sturdy cover (such as a piece of cardboard or a plate)

Set-up:

• Find a large, smooth surface (like a tabletop). Define an area on that surface where you can roll ball bearings, and set up a perimeter around it to keep the ball bearings from rolling away. (You can use towels, double-stick tape or any sort of barricade.)
• In the middle of your blocked-off area, place an object.
• Roll a handful of ball bearing at the object and notice how they bounce off of it. Repeat until you find a pattern. Do this for every object.

Try this:

Have a lab assistant (for example, a family member or roommate) place one of the objects in the center of your experimental area and hide it under the cover. (The ball bearings need to pass under the cover, so they might need to elevate the cover somehow if the hidden object is almost flat.) Can you guess the object based on how the ball bearings scatter?

Pro move:

Map how the ball bearings ricochet off of different known surface types (curved, straight, slanted, etc.). Then ask your lab assistant to find a new object to hide under the cover. Roll the ball bearing at the new hidden object from multiple angles. Can you guess the shape and size of the new object based on the scattering patterns?

Neutrino oscillations

Did you know that subatomic particles can morph? This exhibit uses pendulums to demonstrate this bizarre property in a type of fundamental particle called neutrinos.

Neutrinos are tiny particles with multiple identities. As they travel, they shift between these three unique identities in a process called neutrino oscillation. Physicists hope to learn more about neutrinos’ identities and neutrino oscillations with the Deep Underground Neutrino Experiment (DUNE), hosted by Fermilab.

Goal:

Simulate neutrino oscillations by transferring energy between two pendulums.

Materials:

• 2 tennis balls
• string
• 2 chairs

Directions:

• Place the two chairs back-to-back, ~1 yd (1 m) apart.
• On a long piece of string, make two knots ~8 in (20 cm) apart.
• Suspend the string between the two chairs and attach it to each one so that it forms a taut line. The knots should be between the chairs.
• Glue or tie a long piece of string to each of the tennis balls to create two pendulums.
• Tie the pendulums onto the string between the two chairs at the knots.

Try this:

The two-pendulum system represents a whole neutrino, and each pendulum represents one of its identities. The swinging pendulum is the observed identity—that is, the identity scientists would see if they made an experimental measurement. The static pendulum is its secret identity that could overtake and replace the observed identity if energy is transferred into it.

Swing one of the pendulums perpendicular to the suspended support string. What happens to the static pendulum? Keep watching for a few more minutes. Do you see any patterns?

Pro move:

Neutrinos have 3 possible identities: electron, muon and tau. Can you build a system with three pendulums in which the energy is transferred between all of them?

Higgs field

Ever wondered why light bulbs have mass but the light they produce does not? This last exhibit shows how the Higgs field interacts with some particles while ignoring others.

The Higgs field permeates every inch of spacetime. Particles such as quarks (found inside protons, among other particles) interact with the Higgs field and gain mass. But other particles, such as photons (which you might know as “particles of light”), cruise through and remain massless. 

Goal:

Create a Higgs field out of iron sand to simulate how some particles gain mass while others do not.

Materials:

• iron sand
• magnetic ball
• non-magnetic ball
• white board or any other flat surface

Directions:

• Spread the iron sand evenly on a flat surface (such as a whiteboard or a cooking tray). 

Try this:

Roll the non-magnetic ball over the iron sand, and then roll the magnetic ball over the iron sand. What happens? How does interacting with the sand impact the speed of the magnetic ball?

Pro move:

Place a powerful magnet under your Higgs field and see if you can clump some of the magnetic sand together. The clump of magnetic sand represents a Higgs boson, which is born when the energy from colliding particles is transferred into the Higgs field.