# Science Activity: How Do Pressure Changes Affect the Wind?

By Marlene Gundlach

Differences in air pressure produce winds. In this activity, students will make observations about air pressure and its effect on wind directions.

## Prelab Discussion

Have students read through the entire activity, and then discuss the following:

• Discuss millibars and milliliters of mercury. Point out the units marked on the barometers students will be using.
• Ask students to suggest how barometric pressure changes over a set period.
• Remind students that the wind direction should be given as the direction from which the wind is blowing.
• Have students suggest factors other than pressure, such as buildings, fences, or other obstacles, that might affect their wind measurements.

## Materials and Preparation

Materials needed:

• barometer
• compass
• stick with 30 cm piece of string attached at one end
• copy of data table (Record barometric pressure in the units marked on the barometer. The units are usually millibars or milliliters of mercury. Record wind direction as one of the following: North, Northeast, East, Southeast, South, Southwest, West, or Northwest.)

## Procedure

1. Choose an outdoor spot near your home or school to make measurements of pressure and wind direction. Choose a convenient spot, because you will need to take two sets of observations each day; one in the morning and one in the evening.
2. Use the barometer to measure the pressure. Record the time and the pressure measurement in the data table.
3. Shove the stick in the ground, string end up. Move the stick around until the string is being blown toward you by the wind.
4. Move the compass so the magnetic needle points north. Look down at the compass and the string and estimate the direction the wind is blowing from. Record the wind direction in the data table.
5. Repeat the procedure twice each day, morning and evening, every day for one week. Try to make your observations at about the same time each day.

## Analysis

1. Describe how the barometric pressure changed each day. (Answers should indicate rising or falling barometric pressure and should reflect recorded data.)
2. Describe how the wind direction changed each day. (Answers should indicate the change in direction from which the wind was blowing. The wind may also have been calm at the time of some readings.)
3. Did the wind direction change more on days when the barometric pressure was changing or when the barometric pressure was relatively constant? (Answers should agree with the recorded data.)

## Ideas for Extending the Activity

Have students write a short paragraph explaining what you learned about the relationship between pressure, pressure change, and wind direction. They should explain how the principles discovered can be used every day.

Extension activities:

• Farmers watch the barometric pressure closely to see when pressure starts to change rapidly Although rapid pressure change does not predict a specific type of weather, it almost always means a change in weather. Explain why.
• Develop a hypothesis about pressure change and weather. Does increasing pressure imply better weather and decreasing pressure imply stormy weather? Do research to develop your hypothesis.