How do I demonstrate the speed of sound with simple technology?

Question

As a teacher, how can I use inexpensive materials to build a demonstration of the speed of sound? [And, in a similar vein of thought, is there a way a layman can demonstrate the speed of light?

Answer 1

Great question! For the speed of sound, I think the best demonstration is an outing where you can place a line of student about 100m apart. Give each a flashlight with a button. Get out your video camera and place it on a roof or hill so you can record all of the students. Then rig a simple light on a sound source at one end of the line. For instance, a sledge hammer on a piece of steel with a circuit between them. Make sure the student banging the drum has earplugs! At ~340 m/s in normal air, you only need ten students or so to make this effective. Then just digitize the tape and have them count the number of frames between each light turning on. You can also talk about human reaction times as a bias.

For the speed of light, check out the link. It is doable, but a bit more technical, and not as obvious as the above.

Hope that helps!

Answer 2

Because you are a teacher, I am sure it is politically incorrect to use something like an explosion. Otherwise I would say light some m-80's at night.
I am sure you cant use a gun with a bunch of flash either.
The best thing is to get a sledge hammer and a large piece of metal or wood that makes a large bang when you hit it full force with the hammer. Place the students far away. As a general rule, for every 100 ft away, it will take an extra tenth of a second for the sound to arrive. Hit the metal or wood as hard as you can. The students should see a difference between the time the hammer hits and the time the sound arrives.

Answer 3

The problem arises when you get closer to light speed.. Remember, e=mc^2. A constant acceleration requires energy, and energy has a very small amount of mass. For this reason, you will have more mass as you begin to accelerate, and you will require more and more energy to accelerate that 32.2ft/sec. It is impossible, no matter how much energy you have, to travel at the speed of light.

Answer 4

you can demonstrate the speed of sound with an unobstructed large flat wall of a building, then use something to generate a sharp sound, like hitting two wood blocks together (or just clapping your hands) - you'll hear the sound directly from the source, then again as it goes to and reflects back from the wall. use the difference in the times you hear the sounds to estimate the speed.

lightning/thunder is a good way to demonstrate the relative speeds of sound and light, since as long as the the lightning strike isn't *very* close by, you will see the flash first and the thunder later. (in fact, you can use the difference in the times you see/hear them to determine the distance away the lightning strike was)

Answer 5

An explosion.

I'll explain. If you set a piece of fireworks at a visible distance of 680 meters away, the flash from the explosion will come almost instantly and the sound waves will arrive about 2 seconds later, effectively showing that it took sound 2 seconds (relative to the light arriving) after the explosion occured.

Demonstrating the velocity of light is trickier, and the above example wouldn't work.

Answer 6

The speed of sound, I'm not sure. My best bet would be two microphones one close and one far away, connected to an electronic oscilloscope (can be a computer with the right software) tied in paralell, and see the second one hears it a bit later. Alternatively, you can show the phase shift by tying one microphone to the x axis and the other one to the y axis. (Analog oscilloscope works fine) When they are the same distance, you see a line, when you alter the distances it becomes ellyptic, than a circle.
But, the best demonstration for sound would be 2 speakers some 2-3 metres apart, emitting a single frequency. As you walk past them, you will hear the sound louder and quieter by interference. Thus, you show sound wavelength, which can be "translated" to speed.

Answer 7

With a friend, go to a large level area like a football field. Stand apart from your friend at a known distance (i.e. 100 yards). Have your friend hold two bats apart, while you have your finger on a stopwatch. Have your friend hit the two bats together and when you see this, start the watch. When the sound of the bats hitting each other reaches your ears, stop the watch. You now have the time it took sound to travel a known distance, and you can now calculate the speed of sound.

Answer 8

You can't really do that.

What you can do is state what the speed of sound is, and then relate it to maybe fighter jets, the sonic boom that happens from earth's dense atmosphere, the heat on the aircraft caused by friction, expansion of metals because of the heat, and how designors have to incorporate that into the design.

The SR-71 Blackbird actually grew longer by several inches during flight because of expansion of metals.

Answer 9

I am surprised no one has mentioned used a simple PVC pipe and tuning fork to create a standing wave in a [one] end open chamber.
By knowing the frequency of the sound (which will be given on the tuning fork), one can measure the speed of sound by setting up a standing wave within the PVC tube. When you have placed the tuning fork at a set number of wavelengths away from the closed end of the tube, you should get a resonance sound.
I am not explaining it very well, but you can see additional details here,
http://homepage.mac.com/dtrapp/ePhysics.f/labIII_9.html

As for the speed of light, this can be done by measuring how much a beam of light is refracted in a material of a given index of refraction.
n = c / v
Where n is the index of refraction, c is the speed of light in a vacuum, and v is the speed of light in the material.
Snell’s law,
n1*sin (angle 1) = n2*sin(angle 2)
Using these two formulas, one can calculate the speed of light if a few things are either known (index of refraction and the speed of light in a vacuum) or can be measured (refraction angles).

Measuring these two quantities when time is not a critical factor in the calculations makes the experiment a whole lot easier.

Answer 10

Take a sound meter (most recievers has equalizers with meters)
place the meter with a microphone a few docen yards away from you and make a scream, there will be a difference between the meter registration and the exact time of your scream.

A blanks gun could be useful also. Make a shot from afar. few hundred meters away from students. They will see smoke and flash with difference from the sound registration.