# Helium Rising

### Research Questions:

• What is density?
• What is buoyancy?
• How does temperature affect the density of a gas?
• How does density affect the behavior of a gas?
• Why do changes in the density of air affect weather?

Helium is less dense than air. Density is a measure of the weight of a particular volume of a substance. When we say that helium is less dense than air, we mean that a fixed number of helium molecules in a particular volume weighs less than the same number of air molecules occupying the same volume. The temperature of the frozen balloon is less than the room temperature balloon which is why the helium in the balloon is less dense – and why the balloon in the freezer contracts. The buoyancy of the balloon is affected by the change in density. Since the helium in the frozen balloon is more dense than the room temperature balloon, it rises more slowly than the room temperature balloon. The change in the density of gases explains why hot air rises – and why cold air rushes in to fill the void. The relative difference in the density of a gas as a function of temperature is important to meteorologists because this is how winds form.

### Materials:

• Two inflated helium balloons as close in size as possible
• Access to a freezer big enough to store one of the inflated helium balloons

### Experimental Procedure:

1. Before starting, take a picture of your balloons.
2. Place one helium balloon in your freezer. Leave the other at room temperature. The room temperature balloon is your control balloon.
3. After twenty minutes, take the balloon out of the freezer. Working very quickly, take a picture of the frozen balloon and the control. Bring both balloons outside or to a very tall stairwell where you can release them.
4. Release the balloons. Which balloon rises faster? Why is there a difference in the behavior of the balloons? What happens when cold air is next to the earth? What happens when the sun warms the land?

Terms/Concepts: Density; Bouyancy

References:

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