Flame Tube

Age

Elementary School, Middle School, High School

Format

Stage Show

Materials

   Flame tube
   Propane tank
   Speaker
   Tone generator
   Amplifier
   MP3/CD player
   Cord for portable music player
   Lighter 

Safety Precautions

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.

This demo of course involves fire so be sure to have a fire extinguisher handy as well as keeping the audience a safe distance from the tube itself. Be sure to turn off the propane when done! After the demo, tilt the tube to one end and light the remaining propane to burn it away. You can place one side of the tube on top of the speaker box; this set up seems fairly stable and hasn’t failed us yet. As a word to the wise, be careful where the feet of the tube are as they may slide as you pick one end of the tube up.

Preparation

Make sure the propane tank is full as well as having lighters that are full.

Demonstration

Once the propane tank is connected to the flame tube, turn the tank on and begin lighting the holes closest to the hose. Once all the holes have been lit, you can play a tone through the tube. Play several different tones as to demonstrate the different wavelengths and frequencies. We currently use the frequencies 206Hz and 412Hz and they seem to work pretty well. As a finale, play some music through the tube to show how all the different frequencies appear through the tube. “Iron Man” by Black Sabbath has worked well in the past and seems to fit the visual of fire, though others will work well, too.

What to Say

Traditionally, this demo follows a presentation about waves, normally with the use of slinkies. This is not a requirement, but it makes things easier.

"When I say the word “waves” what do you think of? (Allow for answers, we’re looking for anything wave related including light, sound, radiation or water. Water is what we will go with to continue the presentation) Yeah, water like at the beach right? What do those look like? Perfect, up and down, you got it. There are actually two types of waves; transverse: up and down like water, and longitudinal: side to side. "

"What we're going to do now is actually show you these waves using slinkies! Can I get a volunteer? (Use the volunteer to demonstrate the different waves just mentioned. Laying the slinky down on the floor, hold one end and have them shake their end from side to side to make transverse waves; hold your end and have them push theirs in toward you and back out to make a longitudinal wave) When we move the slinky up and down we can see what we called “transverse” waves earlier. If we push in on the slinky we can get the waves to move side to side. Does anyone remember what these waves were called? Longitudinal, great! These are a little harder to see, but you can see that the slinky gets really close together at some points, and really far apart at others. (Perhaps demonstrate some of the later concepts such as amplitude, etc. by making the waves bigger or smaller, etc.) Thanks you can go sit back down!" (You may even want to use two different volunteers for each wave to increase participation.)

"When we think about this wave (we’ll use a transverse one being made by a slinky for now) what are some ways we could describe it? How big it is, how long it is, how quickly it moves, how many of them there are? Those are all perfect. For starters, let’s look at how many waves there are. This is called the frequency. So you can think of frequency as the number of waves; high frequency: lots of waves, low frequency: not so many waves. Another property we can talk about is how long the wave is. If we look at this length here, the length between the top (peak) here and the top here, that is called the wavelength. Makes sense right, the length of a wave is the wavelength? Perfect. So if you notice, when we increase the frequency, we decrease the wavelength. If you want to squeeze more waves in to the same amount of space, they need to get smaller. Everyone see that? Great. Now, there is another property we can talk about, and that is how big this wave is. This is called the amplitude, a big movement is a big amplitude and a little movement is a little amplitude."

"So now you’re all wave experts right? Exactly. So, let’s talk about sound. Sound travels as a wave, but not an up and down wave like the slinky. Nope, sound travels side to side. Does anyone remember what that was called? It’s not transverse, it starts with an “l”…Right! Longitudinal. Sound is a longitudinal wave, not only that, but sound is a compression wave. Sound travels by compressing the molecules as it travels. It is a little hard to visualize, but longitudinal waves have all the same properties that we just talked about. They have a frequency: the number of waves, they have a wavelength and they have an amplitude. Now, when it comes to sound, those properties have an effect on what we hear. Let’s start with the easy one, amplitude. What do you think a big amplitude means with a sound? Right, it’s bigger or louder. So amplitude tells us how loud the sound is. Frequency is a little hard to guess, so I’ll give you a hint. The number of waves helps us change how the sound “sounds”. Any guesses? Right, higher or lower pitch/tone. So a high frequency is a higher pitch and a low frequency is a lower pitch. "

"So before with the slinky, you could see everything changing, right? Can you guys see sound waves? No, not really. So what we’ve got here is a way to help you visualize sound waves. Let me explain this contraption here. We have this long metal tube, connected to a propane tank and it has a bunch of little holes in the top. So when we fill this up with propane, we can light the gas off the top and it will look like a row of candles. Next to that, we have our speaker, hooked up to a tone generator and an amplifier [these may be unfamiliar words to the audience, so be sure to take extra time to explain just what is going to happen, e.g. “When we turn all this on, this speaker is going to play a single note which will travel through this tube. The tone generator lets me change the pitch from higher to lower (this would be a good time to actually demonstrate the different pitch before lighting the flame tube, so they understand what you're going to be doing). Now we're going to light all the propane.”] So, what do you think this will look like if we play a note from this speaker down the tube? Let’s take a look.

"So what did it look like? Yeah, like a bunch of waves! Let’s look again. See the high spots and low spots? Those correspond to areas of high compression and low compression. Ok, so that was one frequency. What do you think will happen if I change the frequency? I’ll give you a hint; I’m going to increase it. Right, there will be more waves! See, just like you said; increase the frequency, increase the number of waves."

"Ok, so that is just one single note. How often does that happen in real life? Yeah, not too often. So what do you think will happen if we play something like music? Let’s take a look. Pretty cool stuff right?"

Why It Is

Sound waves travel through the air as vibrations referred to as “longitudinal waves”. This just means that the waves oscillate in the direction in which they are travelling. Because of this, they bunch up in some areas and are more spread out in others. When this happens inside the tube, this causes the propane to be compressed in certain areas and as a result it gets forced out of the tube with more pressure. This greater pressure creates a larger flame.

Real Life Examples

Sound waves