Weather Instuments

Thermometer

Thermometers measure air temperatures. Thermometers work because matter expands when heated. Most thermometers are closed glass tubes containing liquids such as alcohol.

Do you think you could make a working

thermometer?

Barometer

A barometer measures air pressure.

There are two types of Barometers: Mercury Barometer and Aneroid Barometer.

A Mercury Barometer consists of a glass tube inserted into a dish of mercury or colored denatured alcohol.

*(If you build your own, don’t use mercury)

The surrounding air presses down on the mercury in the dish and forces some of the mercury up into the tube. The height to which the mercury rises in the tube is directly proportional to the atmospheric pressure.

Think you could make one of these using colored, denatured alcohol instead of mercury?

Psychrometer

A psychrometer measures the humidity of the air. One of the two thermometers has a wick (cloth cover) which is dipped in distilled water.

Evaporation of water from the wick on the wet bulb thermometer leads to cooling.

Using a Relative Humidity Table, the temperature difference between the two thermometers gives the relative humidity of the air (in percent).

This is an example of the type of table you would use. Your book might also have an example.

One such psychrometer is a Sling Psychrometer.

Measurements are taken by whirling the psychrometer with the handle.

See if you can calculate the

relative humidity of

the class room. How

does it compare to the relative

humidity outside?

Anemometer

An Anemometer measures the wind speed. The cups catch the winds, turning a dial attached to the instrument.

Think you could build one of these?

Time for a little review!

1. If I wanted to find out if the pressure was rising, I’d use which of the following?

2. Used to determine the relative humidity.

A) ThermometerB) BarometerC) PsychrometerD) Wind VaneE) Rain GaugeF) Anemometer

3. Can help you find out the wind speed.

4. If I wanted to know the difference between the temperature inside and outside of the classroom.

A) ThermometerB) BarometerC) PsychrometerD) Wind VaneE) Rain GaugeF) Anemometer

How did you do? Here are the correct

answers1.Barometer2. Psychrometer3. Anemometer4. Thermometer