Lesson 2: The roles of pressure and differential heating in wind

Activity 1. What is pressure

This lesson is composed of both class demonstrations and hands-on activities during which students learn how pressure, density, and differential heating play a role in creating wind.

Materials:

• Balloon or bicycle tire's inner-tube
• Bike pump
• Safety goggles

Advanced Preparation:

Gather the materials together; read through the procedure before class

Time needed: Teacher Prep - 10 minutes; Class demonstration - 20 minutes

Procedure:
Introduce the idea of pressure by asking students: What words are often used by meteorologists talk about winds and weather systems? You often see Hs and Ls on weather maps right? What are do they stand for? High and low what? (Elicit the response of pressure.)

1. Inflate a bicycle tire with a pump or inflate a balloon.
2. While you're inflating the balloon/tire, ask the class what’s happening (Air is going into the balloon/tire, the pressure is increasing, the balloon/tire is getting bigger). As you add more molecules into a given space (volume), does the pressure increase or decrease? (It increases because there are more molecules. The pressure inside the balloon/tire is greater than the surrounding air.)
3. Pop the balloon or use a pen to release the pressure from the tire. If possible have the students feel the air being released from the tire.
4. Ask the students what happened when the balloon popped or the tire's pressure was released. (Emphasize that the pressure is equalizing suddenly; the air moved from the balloon/tire to the surrounding room. Before the balloon / tire was popped, the pressure gradient was high between the inside of the balloon/tire and the surrounding air.)
5. Review with the class what happened with the balloon/tire. (you filled the balloon / tire with more air, the pressure inside increased and was greater than the pressure of air in the room, then the pressure was suddenly released when you popped the balloon/tire)
6. Ask the class: which direction does air move when there is a pressure gradient (high to low pressure, or low to high) (From the balloon to the surrounding air - from high pressure to low pressure)
7. What is this movement of air is called? (Wind!)

Closing the activity: Summarize to your students: From the previous lesson, we’ve learned that convection influences wind and today we’ve learned that pressure influences wind. What does temperature have to do with weather? We’ll see in this next activity.