AIR, FLUIDS & DENSITY
• An empty plastic bottle (can be from 8-16.9 oz in size)
• 1 oz of vinegar
• 1 teaspoon/7 grams of baking soda
• 12-in or 10-in balloon
• Bowl of very cold water
• Bowl of very hot water (adult supervision required)
• Learn what molecules are, and how they help us understand gases (like air)
• Learn what fluids are and how they behave
• Learn what density is, and what it has to do with molecules and fluids
• Learn how density can be changed by adjusting other factors
Instructions, Part 1
1 Add the vinegar to the bottle, using the funnel if needed.
2 Fit the opening of the balloon over the narrow end of the funnel and turn it so the wide end of the funnel is up in the air.
3 As you hold the balloon and funnel securely together, pour the baking soda into the funnel so that it goes down into the balloon.
4 Remove the funnel from the balloon and set the funnel aside.
5 Keeping the bottom of the balloon level so the baking soda stays trapped inside, stretch balloon opening over the opening of the plastic bottle until a seal is formed.
6 Once the balloon is attached to bottle, tip the balloon up to empty the baking soda into the bottle.
Background Information, Part 1
The reaction of vinegar and baking soda combining produces a gas called carbon dioxide (CO2). The balloon inflates because the gas needs more space than what is available in the bottle, so it starts to fill the balloon as well. Gasses, like CO2 and air, take up space.
In the AMA Jr. Camp video that accompanies this activity, you will see another demonstration using CO2 gas, like the gas you created inside the bottle and balloon. The demonstration will show that gasses like air and CO2 are fluids, which is important for understanding how aircraft fly through the air.
Instructions, Part 2
1 Remove the bottle cap (if necessary) and stretch the empty balloon over the opening of the bottle to form a seal, as you did in Part 1.
2 Immerse the bottom of the bottle in the bowl of cold water. What happens? Nothing! The air molecules are condensing (moving closer together) because of the cold.
3 Now immerse the bottom of the bottle carefully in the bowl of hot water. What happens? The balloon should start to inflate. The air molecules are spreading out, taking up more space because of the heat.
4 Return the bottle to the bowl of cold water. What happens? The balloon should deflate a bit, because the molecules are condensing back together again due to the cold.
Background Information, Part 2
The amount of air in the bottle is always the same, because it is sealed by the balloon. The air is changing density, or the amount of space its molecules take up. Cold air takes up less space (is more dense) because the molecules are closer together. Warm air takes up more space (is less dense) because the molecules are more spread out.
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