University of Virginia
Physics Department

## Growing Balloons

A Physical Science Activity

2003 Virginia SOLs

• PS.1
• PS.2
• PS.5
• PS.6
• PS.7

Objectives

Students will

• Observe the balance of kinetic energy and molecular movement resulting from heat energy;
• Compare direct relationships of temperature, pressure, and volume;
• Examine different states of matter conducting heat.

Motivation for Learning

Preliminary Class Questions For Teacher Demonstration

Hold up a medium to large size balloon that is blown up with air. Ask the students the following questions:

1. How would this balloon react to temperature changes?
2. What predictions can you make about the air molecules inside the balloon? (Will they react evenly or unevenly against the balloon's sides?)
3. Is there equal water vapor inside and outside the balloon?
4. When heat is applied to the balloon, how many methods of heat transfer can you identify? Where will the heat be applied?

Teacher Demonstration Materials

1. Two balloons
2. A radiating heat source (a lamp, hot plate, or sunlight)
3. Cooling materials (ice cubes, cold water, or refrigeration)

Teacher's Resource Answers for Preliminary Class Demonstration Questions

1. The balloon expands when heat is added (absorption) and contracts when made cold.
2. The air molecules expand and contract evenly.
3. Yes, there is water vapor on both sides. A greater amount is inside, because when we blow it up, we have more water vapor in our lungs.. This will "add" to the expansion and pressure.
4. Two methods are observed - conduction and convection.

Teacher Demonstration Procedure

1. Blow up 2 round balloons 3/4 full with air.
2. Roughly measure the diameter of each balloon with a ruler, and record the measurements on a blackboard.
3. Warm one balloon with a radiating heat source like the lamp.
4. Expose the second balloon to cold temperatures like putting in ice cold water..
5. Expose both balloons to temperatures until expansion and contraction are clearly visible.
6. As the changes become visible, the Preliminary Class Questions should be discussed.
7. Measure the new diameters of each balloon.

Background Information

Content areas observed in this activity are the states of matter, particle motion, kinetic energy, heat absorption, heat transfer methods, volume, pressure, and temperature. In each phase of matter, particles are in constant motion. Their phase speed is altered with the addition of heat energy. This addition increases the kinetic energy of the particles. Their collisions and friction increase the kinetic energy.

Molecules in each phase reflect heat absorption by changing volume. "Escaping" particles extend the material's volume as their speeds increase. When a boundary exists (like our balloon), the particle movements determine the force against the boundary. This creates pressure.

Particle movement determines temperature. The kinetic energy in one area may be different from another area. In the teacher demonstration, we observe Boyle's Law and Charles's Law as follows respectively: "If a sample of gas is kept at constant temperature, decreasing volume will increase the pressure that the gas exerts on a surface. If a sample of gas is kept at constant pressure, volume increases as the temperature increases." The ideal gas law is stated as pV = nRT, where p is pressure, V is volume, T is temperature, n is the number of moles, and R is the ideal gas constant.

Another factor affecting the size of the balloon is heat transfer. Initial densities of solids, liquids, and gases display varying kinetic energy changes when heat is transferred to the system. These interrelationships are the basis for the student activity.

### Student Activity

Materials (per group)

• One round balloon
• One blow dryer (may have to share)
• A marker

Procedure

1. Blow up one balloon 3/4 full of air.
2. Tie off the end.
3. Gently mark areas: 1 near the tied end, 2 in the middle, and 3 at the far end away from where it was tied..
4. Record a PREDICTION in the data chart - Will the balloon expand evenly or unevenly as it is heated? If you predict unevenly, which areas will show effects of temperature, volume, and pressure first? Last?
5. Compare and discuss reasons for your predicitons.
6. Hold the balloon at the tied end.
7. Point the blow dryer 4 to 5 inches from the tied end.
8. Turn the dryer on high heat and hold until changes are visible.
9. Record your observations in the data chart.

Extensions

The activity could also be done by putting the balloon into cold water and observing what happens. In this case use a similar data table and answer the same assessment questions.

Internet Research Topics
Use the Internet to answer the following questions:

A. Using vocabulary terms from the student questions, how does a helium research balloon fly?
B. How do the terms apply to the new ULDB (Ultra Long Duration Balloon) research balloon and its flight?

Students with Special Needs

All students should be able to participate in this activity.

Click here for further information on laboratories with students with special needs.

Assessment

Observations

1. Describe what happened as the balloon was heated.

2. Which areas, if any, contracted as they were heated?

3. Which areas, if any, expanded as they were heated?

4. Did any areas appear not to change? If so, which ones?

5. Which of your predictions were correct? Which ones were wrong?

Complete the following questions on a separate sheet of paper:

1. How was the teacher's demonstration balloon's behavior different from or the same as your balloon's behavior?
2. Based on your observations, how would you use each of the following terms to explain what happened?

Heat Energy
Kinetic Energy
Temperature
Pressure
Volume
Particle Motion
Expansion
Contraction
Conduction
Convection

Which of the factors above had the greatest effect on the activity of the balloon?