Vacuum Buzzer

Need some space and quiet?

If you're trying to change your surroundings, maybe you should think about traveling vertically. You know what a car horn sounds like in outer space? Nothing!

Sound needs something to move through, and if you take away the air, then you take away sound's pressure wave. An experiment to look at sound in a vacuum was first done 400 years ago by Sir Robert Boyle, and you can see many versions all over the internet of people sticking buzzers in bell jars.

This is a way that you can do that same experiment but in the palms of your two hands. Let's space!

What: No Sound in Space: the handheld version

No, What?: I CAN'T HEAR YOU!

Concepts: Sound, pressure, waves, vacuums

Time: ~ 20 minutes

Cost: ~ $5 (all re-usable)

Materials:

• Buzzer (rated at 12V DC work great, and at way lower than 12V)
• Disc Batteries x 4 (most are 1.5V, and 6V should do trick)
• Jumbo Syringe
• Rubber bands
• Tape
• String (optional, but preferred)

Let's get vacuuming!

Step 1: Prep Your Buzzer

The grand champion of this experiment is our buzzer, so we want to get it all nifty.

Start by stripping the wire ends about an inch or so. Use some aluminum foil, fold them around each lead, and squish them so the two contact ends are like metal pancakes. This will give us greater surface area to contact our battery pack.

Step 2: Battery Sandwiches, Anyone?

Start with a series of 1.5V disc batteries, and put them together in the same orientation. You can rubber band them together and tape the sides, too. DO NOT HOT GLUE THEM.

Test out the polarity of your buzzer, and enjoy it's shrill note of science. Choose of the leads to have permanently attached, and slip it under the rubber bands on one side of the battery sandwich. Tape it down so it's nice and secure.

Test contact with the other lead to make sure that you'll be able to make the buzzer go when it's primetime.

Step 3: Tube Time

Remove the plunger of your syringe, and it's go time. Slide the other contact on to your battery sandwich and tape it on. You'll now be drowned in the sound of a constant buzzing, UNTIL.......

Press the plunger as far down as you can to get the buzzer and battery right at the end of the syringe. Place your thumb over the tip, and then pull the plunger back as far as you can. As the volume of air increases, the volume from your buzzer decreases. With your arm alone, you can probably get down to 0.2 atm. The air is thinner for propagation against the sides of the bottle, and so less of it reaches your ear. Imagine if our plunger could go into infinity, and there just a few molecules zooming about. That's space, and that's quiet. :)

Step 4: Techniques and Alterations

Science isn't always easy, so here are a few tips and tricks for getting the most of this experiment.

The number one thing that can happen is the vibrator sits against the plastic and vibrates that. The sound propagates directly through the solid, and thus the buzzing remains constant regardless of air pressure. This is neat in it's own right, but not what we're going for.

If this is happening, three things you can do:

• Tie to a String: If you're feeling tricky, you can tie a piece of string from the tip of the syringe to the buzzer, so that is suspended in the middle of the syringe. This is the most effective method.

• Add Sound Battening: You can add felt or anything else to mute direct vibration allowing the sound experiment to come through.

• Flip the Syringe: Do the experiment with the plunger going down toward the ground. This allows the battery pack and buzzer to sit on the rubber, and is relatively muted in comparison.

For more on the science of sound, you can read about acoustic impedance, read this quick primer on sound propagation, and even check out this reddit response about sound at altitude.

Have fun, keep exploring, and make sure to bring a writing pad if you're hanging out in space. :)