To demonstrate how heat affects the strength of air pressure
- Wide-mouthed jar
- Round balloon filled with water
- Matches or lighter
- Sheet of paper
Fill the balloon with water until it is slightly larger than the mouth of the jar. Roll the paper (top to bottom) and place it halfway into the jar. Light the paper on fire, and drop it completely into the jar. Place the balloon on top of the jar.
The balloon is sucked into the jar because the burning piece of paper heats the air molecules and causes them to move away from each other. Some of the heated molecules will escape the bottle, causing the balloon to vibrate prior to it being sucked in. When the flame goes out, the air is cooled down, and the molecules move together again. This is what causes the vacuum. Under normal conditions, the outside air would come rushing back into the bottle, but it can’t due to the water balloon. The air pressure is so great outside the jar; it pushes the balloon into the bottle. The balloon cannot be removed from the jar until the air pressure outside and inside is balanced. The balloon can be removed by pushing a straw halfway into the jar; this balances the air pressure.
You can use a boiled egg in a milk bottle like we’ve done in the video too!