Science Buddies: "Ask an Expert"

I need to have an experiment to show how dolphins communicate. I have to have my material list by tomorrow. Of course I have waited until the last minute. Please Help!!!!

Hi kykoyote,

I'm afraid I don't quite understand what sort of project you're planning. Are you interested in the types of sounds dolphins make? The way sound travels under water?

If you aren't sure yet what to do, try a few google queries to look for ideas.

Good luck,
Erik

I need to how the sound waves move thru the water and a way of proving this.

Hi Kykoyote,

If this is more of a research project than an experiment, I may be able to point you toward some suitable reference material. In general, it's a good idea to start out with your local library, a few google searches, and then once you've identified some relevant key words, searches in an online citation database, (for example google-scholar http://scholar.google.com/, or subject-specific databases.)

If you're hoping to build an experiment, you'll probably have to come up with a more specific question to answer. Underwater sound is a big topic, and there are people who have spent their whole lives studying various aspects of it.

For example, something like "how fast does sound travel in water," or "is the speed of sound in water different for different frequencies," or "what effect does temperature or salt content have on sound speed" are examples of questions you could probably test.

Those particular ones could be rather large projects and would take some time and either some borrowed equipment or a lot of ingenuity - but there are others that might be easier to do. The simplest possible question would be something like "can sound travel underwater," which you could answer using a swimming pool or a bath tub and your own ears.

If you live near the ocean or a large river or lake, you could take a different approach and ask something like "what sort of sounds are there in the underwater environment at some particular place?" Then you've have to go out and record them.

Finally, you could turn it into an engineering project by asking something like, "is it possible to record underwater sound with a device fitting some requirements?"

I'd be happy to help offer advice as you design a project. A couple quick questions which might make it easier for me (or others here) to help you:

1 - What grade are you in?
2 - How long do you have to work on the project? (And how hard do you want to work on it?)
3 - What math classes have you had?
4 - Have you had any experience with electronics or with building mechanical things out of wood/pvc-pipe/etc?

Good luck,
Erik

I talked with my science teacher on what exactly I have to do with my dolphin project. I need explain and come up with a demonstration on how echolocation works among dolphins. I know that they communicate with whistles and different noises, but am kind of lost on how I can show this. I am only in sixth grade so I have not worked with electronics and stuff a whole lot. I have done al lot of research and I am not having too much trouble writing the research paper, I just do not know how I can demonstrate how this works. Thanks for any ideas you might have.

Hi kykoyote,

Thanks for the additional information.

Sounds like a neat topic. It may be a little difficult to do much with it experimentally, but you can probably come up with something that will work. I should mention that it's something I've never played with, and I don't really know what will work and what won't, but here's an outline of one possible experiment. Not sure if it's what you had in mind, but at least might offer some worthwhile ideas to get you started thinking of something else.

One experiment you could try is to have a sound source and a microphone held next to each other underwater. Then you could place a big hard object at different distances away from them and see if you can record an echo off the object. The object could be one of the walls of your tank, or something like a big brick or cutting board. You can then (hopefully) see the sound and its echo by looking at the recorded waveform on a computer, and compare the distance to your object to the delay between the sound and echo.

The only complication is that it's much more likely to work if you do it in a pool of water that's a lot bigger than the distance between objects. Also, since sounds travels much faster in water than in air, you'll need a very short duration sound and you'll want to place the source and object as far apart as possible. Something like a swimming pool or a big pond would be best if there's one in your neighborhood. If not, then you might possibly be able to use a bathtub or a big barrel if you are able to make a very clean sound. If you have access to some hand tools (like a hack saw) and can spend $10-$20, another idea would be to use a length of pcv pipe (plastic drain pipe) from a hardware store. You could put end caps on the pipe, lay it horizontally, cut holes along the top, and fill it with water.

What do you use for a noise source? I'm not sure. It's hard to make noise underwater, and it's hard to make sounds which die off quickly. You're best bet is probably banging two things together. Since sound travels fast (approximately 1500 meters per second) in water, the duration of the sound has to be really short so that you can see the echo. (Less than 0.001 second if your source and object are a meter apart.) Play around with various objects to try to find something suitable. The best candidate I've been able to find after a few minutes of tinkering in my office here is snapping a nail clipper closed - but I haven't tried it underwater.

To detect the sound, you may be able to waterproof an ordinary microphone. Take the cheapest microphone you can find (one no one will miss in case it gets damaged, for example one of those little plastic encased computer mics), and stick it in the finger of a latex glove or a balloon. Squeeze as much air out of it as possible. Then tape up the end with electrical tape, or else tie it with rubber bands and add some rubber cement or hot glue to make it watertight. Stick it underwater, and see if it works. I've heard that it does work with a latex glove and some types of microphone, but have never done it myself If it doesn't work, I can suggest some things that might improve it, but will probably require destroying the microphone housing.

Some complications you may run into are noise from floor vibrations / pump-motors / traffic / people in the water making it hard to see the echo, and trying to find a sound which is very short and also loud enough to work. As I said, I've never done this or even heard of anyone doing it, so there's no guarantee it will work at all.

Finally, another option is to do the same kind of experiment in air instead of water. The physics is pretty much the same, and it would be a whole lot easier to do.

Good luck,
Erik