Air pressure and volume with some simple experiments

We have studied air and the effect temperature has on it previously. As I do like to return to previous topics to deepen the learning, and also, I found this really nice experiment on YLE (public broadcasting company in Finland) I decided to look into the topic again.

For this experiment you need:

  • a glass bottle
  • two bowls
  • a balloon
  • hot water
  • cold water (ice is a good addition if you have some)
  • some way to measure the temperature of the liquids. We used an electric thermometer used to measure stuff when cooking
  • a pen and paper for writing the temperatures down (optional)
  • About 20-30 minutes of time

First, we measured the room temperature (M1 in image 2), which was 20 degrees Celsius. Then we added the hot water in one bowl and cold water and ice in the other.

Second, I placed the glass bottle in the bowl with the hot water. Then we measured the temperature of the water. It was 70 degrees Celsius.

I then put the stick measuring the temperature into the bottle and waited a bit and measured the temperature of the air inside the bottle. It was 46 degrees Celsius. I could have waited longer, but patience is not the virtue of five year olds.

Fourth step was to place the balloon on top of the bottle to hold the air in at the volume it was in the hot water. Once the balloon was in place, I transferred the bottle into the bowl with the cold water. I asked my daughter to hold onto the bottle as it was in the cold water as that is quite safe to do.

Top left: necessary items for experiment. Top middle: bottle in hot water. Top right: taking the temperature of the air in the bottle. Bottom left: adding the balloon. Bottom right: beginning of the reaction when the bottle is transferred to the cold water bowl

Top left: necessary items for experiment. Top middle: bottle in hot water. Top right: taking the temperature of the air in the bottle. Bottom left: adding the balloon. Bottom right: beginning of the reaction when the bottle is transferred to the cold water bowl

Then we waited to see what would happen. Pretty soon the balloon was sucked into the bottle with a plop. We then took the temperature of the cold water, which was 6 degrees Celsius and discussed why this happened.

Hot air takes up more room than cold air. When the temperature drops, the atoms in the air are less excited and are closer together. When the air temperature rises, the atoms get more excited and move more and need more space. This space needed is the volume. So when the air in the bottle is hot, there are less atoms of air in the bottle as less are needed to fill the volume of the bottle. Then when we place the balloon on top, we stop air moving to and from the bottle. Then, as the air cools inside the bottle, the atoms take up less space and the air pressure in the room finalises the deal by pushing the balloon into the bottle to try to even out the pressure differences. This goal to even out differences in air pressure is the reason for the everyday phenomenon of wind.

air pressure and volume experiment

The result of the experiment and our measurements


If you have questions about these experiments or instructions, leave me a comment and I will improve these instructions. Also, please remember like and share if you find this useful.

Copyright text and images: Satu Korhonen. You are free to try these experiments out, use them in your teaching. But instead of copying the text or images, link back to this page.

 

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