How Density Differences Lift a Balloon

Begin with the conductivity sheet and the particle model of conduction. Then use the house and balloon sheets for types of transfer, and the lunch carrier, heat sink and fabric sheets for design and data.

Explain why a hot air balloon rises with air density, then find the mass of air in its envelope. The directions on the page read: Read the text and study the diagram and table. Then answer the questions on page 2. An answer key is included.

Yes, both. We made it for 7th grade energy, and it works the same at home or at school. At home, a student can work through it alone and then go over it with you, which shows quickly what is solid and what needs another look. In class it works as independent practice, homework or a warm-up, and you can print one copy or a full set.

Conduction passes energy between particles that touch, and the particles stay in place. In convection a heated fluid expands, rises, and carries energy with it while cooler fluid sinks.

Materials such as wool and foam board trap still air, which conducts energy poorly. Sort Materials by Thermal Conductivity lists values for 12 materials from silver to still air.

With the same energy supplied, 200 g of water rises less than 100 g of water, and 100 g of cooking oil rises differently from water. Energy Transfer, Mass and Temperature Change has students graph all three.

Heated air spreads out and becomes less dense than the cooler air outside, so the outside air pushes up on the balloon. How Density Differences Lift a Balloon also finds the mass of air in the envelope.