NORTHWEST WEATHER WATCH

Overview

Students will work in cooperative groups with one student recording information onto the Lab Sheet. Materials for each group:

• a balloon
• a narrow-necked bottle
• a pan of hot water
• 1 Lab Sheet

Anticipatory Set

The teacher will ask the students to describe how they would "blow up" a party balloon and then ask them to demonstrate. When the students have done this, the teacher will ask students what they thought happened when they "blew up" the balloon. (Students will probably conjecture that they put more air into the balloon and since air takes up space, the balloon expanded.)

Another example of this procedure is pumping air into a bicycle tire. Students may brainstorm other times they might use a pump or blow air into an object (inner-tubes, rafts, mouth to mouth resuscitation.) The teacher should then ask if there is any other way to "blow up" the balloon. In this experiment they will be blowing up a balloon without putting any more air into the balloon. The goal is to have students construct a procedure using the given materials (balloon, bottle, pan of hot water) which will cause the balloon to inflate even though no new air is being pumped into the system.

Class Discussion

Now the teacher will ask students to get into groups and answer the question:

How can you blow up a balloon without blowing?

Next the teacher will distribute the materials and give the students their task:

1. Devise a way to inflate your balloon with the given materials.
2. Record your plan in the hypothesis section of the Lab Sheet. "We will inflate the balloon by...."
3. Record the steps of your procedure and your observations onto the Lab Sheet.

If students were not successful in using the materials to inflate the balloon, they should devise another procedure.

Class Discussion

Students share their results which should include:

1. What they did (the steps of their procedure). Students should have stretched the balloon and pulled it over the neck of the bottle. They should then have placed the bottle of air in the pan of hot water to heat it.
2. What was actually happening (i.e. why the balloon expanded even when no "new" air was introduced into the system.) As the air warmed, it rose and took up more space (expanded), causing the balloon to stretch.

Explanation, Observations and Conclusions

Students should have reached the conclusion that air rises and expands when it is warmed. The balloon secured onto the bottle was a closed system. No new air was introduced by blowing or pumping. When the bottle was at room temperature, the balloon did not inflate. When the bottle was heated, the air inside was warmed as well. The warming process caused the air to rise and expand.

Students should be encouraged to generalize their findings to other areas. For example:

What happens to the air in pneumatic tires on a hot summer day?