Thermal Conductivity (Eric Lee)

Quickwrite

Title:

Fireproof balloon

Principle(s) Investigated:

Heat convection, introduction to thermal conductivity

Standards:

MS-PS3-4 Energy. Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the particles as measured by the temperature of the sample.

Materials:

Candle, balloon, water, safety glasses, matches, plate (for candle in case balloon with water pops, less spillage)

Procedure:

• First blow one balloon with air.
• With a second balloon, fill with some water, then blow the rest with air about the same size.
• Put on safety goggle and light candle.
• Demonstrate with the empty balloon with air what would happen when when put near flame. Ask for predictions.
• Either tell the students that there is water in the second balloon or demonstrate what would happen to the balloon with water inside when put near the flame. Is their prediction the same as the first balloon?
• Observe and record data! Discuss what happened.

Student prior knowledge:

Heat transfer, specific heat capacity of water

Explanation:

The balloon filled with air bursts since the air expands quickly and does not absorb the heat from the rubber which causes the rubber ball to stretch and eventually brake to let the expanded air out. The balloon having water and air does not burst. It is because water absorbs the heat from the rubber band and through convection currents it carries the heat away from the rubber while cold water replaces the risen water.

Questions & Answers:

• Why does the balloon with no water break in the flame?

A: The empty balloon is only filled with air. When heat is added, it weakens the bonds of the rubber balloon. As you heat the air inside the balloon, the air molecules push against the weaken part, so the balloon pops.

• How does the balloon with water in it resist breaking in the flame?

A: The balloon with water uses the water to absorb the heat. This prevents the rubber of the balloon from gaining a weak point in the balloon, hence does not pop.

• If you turn the balloon with water so that the flame is close to the side of the balloon with water, will the balloon pop?

A: Yes! Because the water is not conducting heat away from the surface of the balloon.

Applications to Everyday Life:

• Sweat - When you exercise, you may sweat which helps regulate the temperature of your body. As it evaporates, it takes the heat energy with it, leaving a cooler feeling on your skin.
• Special absorbent polymers - Some have been implemented in some homes to help fight against fires. The water in the foam helps absorb some of the heat energy from wildfires and such to help buy time for firefighters to fight flames.
• Automobiles - Car engines generate a lot of heat. The radiator uses convection, conduction and radiation to keep the engine cool. Both air cooling and water cooling systems are in use for automobile engines. With air-cooling, the heat passes from the engine directly to the atmosphere. With water-cooling, the water merely serves as a medium for transferring heat from the engine to the radiator, which gives it off to the atmosphere.

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