Home made barometers and themometers....?

Question

what is the difference between the two home mades? who's to say that the barometer won't measure temperature? it's made pretty much the same way, so i don't really understand. how do i know that my home made barometer actually measures air pressure, and not tempurature?

http://www.energyquest.ca.gov/projects/thermometer.html

http://fi.edu/weather/todo/barometer.html

oh, and why do i need to use achohol for the thermometer, why can't i just use water?

Answer 1

You can't use water because it will freeze at zero degrees.

Answer 2

You are correct in this respect that a barometer measures the air pressure and the temperature also influences it.

It works like this: When I fly my aircraft, I set my altimeter, which is in fact a barometer, to what is called QNH; the air pressure of my present place but as sea level, which is the standard reference. Those standards, called Standard Atmosphere (SA) is what is used to calibrate all instruments but especially in aviation. It is: 15 degrees Celcius and 1013.25 hPa pressure.

But when I fly in the winter, I fly lower than that and, in a hot summer day, higher than that. But those are not too important to create a danger to navigation.

Meteorolog draw isobar maps. To do so, they need to get all data over a very large region like the entire Europe, and draw equidistant lines. For them, QNH, based on observed pressure and corrected for a column of air going to sea level at SA pressure, is not good enough. They use another standard: QFF. That is the same as QNH but the value of the column of air representing the elevation is not SA but a monthly or weekly value that varies for the season of the year.

So, your reasoning is correct but the thermometer and barometer show in those exercises are not useable for aviation or any other professional occupation. But I am sure they are fun to make and teach a lot about physics. Have fun!

Answer 3

Sod it just drink the alcohol , cant see the barometer working either , unless the air pressure rises rapidly , the water will evaporate quicker than any noticeable rise in level , could be why there is Mercury in them