# Hard waves and sound question!

1. Dec 14, 2009

### persian52

1. The problem statement, all variables and given/known data

Design an experiment to determine the temperature outside.

Materials:
2 blocks of wood
stop watch
Measuring tape

3. The attempt at a solution

I believe it has something to do with measuring the rate of flow of a viscous liquid down a ramp.
The colder the temperature, the less distance per second the fluid travels.
Once baselines are established at known temperatures, it would be a fairly reliable instrument.

BUT

the thing is we cant use any type of liquid!
we have to do it with all the materials we have and nothing else...

2. Dec 14, 2009

### Pythagorean

my first impulse is to say thermal expansion, but I don't know what you'd need the stopwatch for. You could just leave one block outside and one inside for a really long time, but you'd also have to know the temp inside for this to work:

http://en.wikipedia.org/wiki/Thermal_expansion

But then, you're title has nothing to do with thermal expansion.

3. Dec 14, 2009

### persian52

i got ur point, true

4. Jun 11, 2011

### jtebb

Not sure if anyone cares, but to measure the temperature outside with this equipment, one could determine the speed of sound, which varies with temperature according to v=332m/s + 0.59T, where T is the temperature in degrees celcius.

Using the equipment, clap the boards about 200m from a wall, and measure the time taken for the echo to return (a trip of 400m). To make more accurate measurements, set up a rhythm of clap-echo-clap-echo and measure multiple trips. The averaging will minimize start and finish reaction time delays. Counting 20 round trips for example, that's 20x400m = 8000m in whatever time is measured with the stopwatch. v=d/t will give you the speed of sound on that day. Then use the speed of sound equation and solve for T, the temperature.

Cheers!