Pressure, Volume and Temperature

By Cathy Lenox
MICDS
Edited by Anna Mracek and Ray Arvidson

What is Pressure?

Pressure is a basic physical property of a gas. It is measured as the force exerted by the gas per unit area on its surroundings.

What is Volume?

Volume is the amount of space that something takes up. Solids have a fixed volume and shape. Liquids have a fixed volume but take the shape of their container. Gases take the volume and shape of their container.

What is Temperature?

Temperature is most commonly thought of as how hot or cold something is. More precisely, temperature is related to the measure of the average kinetic energy of the particles of a sample of matter. This matter can be in any state. Matter is made up of atoms and molecules, and these particles are constantly moving. (Only at 0 Kelvin does all motion stop. This is known as absolute zero, and represents the lowest temperature possible.)

The Relationship between P, V, T and Solo Spirit:

The relationship between gas volume (V), pressure (P), and temperature (T) can be expressed by the ideal gas law:

= constant

where P = pressure of gas, V = volume occupied, and T = temperature.

In simpler terms, if volume is constant, an increase in temperature results in a proportional increase in pressure.  If pressure is constant, an increase in temperature results in a proportional increase in volume.  Inversely, if volume is decreased and pressure remains constant, temperature must decrease.  Basically, pressure and volume are directly proportional to temperature and inversely proportional to each other.

The Aerobot Payload instruments on Solo Spirit measure pressure and temperature at various altitudes as the balloon flies in the Earth's lower atmosphere, known as the troposphere. Pressure and temperature are both controlled by the ideal gas law. However, because the volume is not held constant (that is, the atmosphere can expand and contract), the relationships between pressure and temperature are complex. Generally, temperature and pressure decrease with altitude in the troposphere. Temperature decreases linearly with increasing altitude, whereas pressure decreases exponentially.

Find Out More!

To learn more about the effects of temperature and pressure on the human body, go to About the Pilot!

To view pressure and temperature data recorded by the onboard sensors in the last hour, go to Science and Payload Data!

Activities:

Your Own Balloon:

Blow up two similar balloons.

Let them sit for several minutes until their temperatures match the room temperature.

Measure the room temperature with a thermometer.

Measure the circumference of each balloon at the widest spot with a piece of string or a measuring tape. Record these measurements.

Place one balloon in a refrigerator or freezer, and keep the other balloon at room temperature as a control.

Measure the temperature inside the refrigerator or freezer with the same thermometer.

Leave the balloon in the refrigerator or freezer for about an hour.

Remove the balloon and measure the circumference around the widest spot as quickly as possible.

Compare this measurement to the measurement made before the balloon was placed in the refrigerator!

Allow the balloon to warm back up to room temperature and measure again! Also measure the control balloon.

Now compare the numbers. What is the relationship between temperature and volume? Does the pressure stay the same inside of the balloon? Why or why not? Use the control balloon to make sure the refrigerated balloon did not leak. How would you do this?

Get Involved with Solo Spirit!

Look at the data for the first 24 hours of the Solo mission and plot the pressure and temperature data that are recorded by the onboard sensors on the same graph. (You can get the data here.) Do you see a trend in the data points?

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