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Easy
30 min
Have you and the kids ever noticed when you drive high up in the mountains, your bags of chips seem to expand, and then when you drive back down, your water bottles all start to collapse inside themselves? That’s because the air pressure changes when you go up and down in altitude.
For this Waypoint, we’re staying inside to experiment with air pressure to get us prepped for all the fun times and fun ways you can see it in action outdoors. Cold air in the wintertime causes the air pressure to drop even more, so it’s the perfect time of year to get out and see those changes in action!
For this experiment, we’re going to heat up water inside our aluminum cans, and then see how the cans react to a sudden change in temperature by dunking it in ice water.
The water is going to help us displace some of the air in the can, and then the ice water will help us create a drastic difference in air pressure between inside the can and outside.
Have your kids add about 4-5 tablespoons of water to each can. Don’t add too much, or it will take long to heat, which is our next step.
Using your tongs, set the two cans into your frying pan, and turn the heat up high.
We want to heat them up until the water inside turns to steam and starts coming out the top. When the water starts to steam, it will take up more space than the water, thus pushing the air out of the cans.
This will take some time, though, so as the cans heat, let’s move to the next step. But keep an eye on them!
Now we need to create an ice bath to dunk each of our cans in. This is the crux of our experiment. The colder the water, the more drastic the change in pressure, and the more spectacular the results.
Fill your bowls up with cold water and ice cubes. There should be more water than ice to allow you to dunk the cans in the water, but enough ice cubes to ensure it’s ice cold.
Place the bowls as close to the stove and your frying pan as possible. You want there to be a very short distance between them.
When you notice your cans are steaming, you know it’s the moment of truth. Everything will happen quick with this step, so gather all the kids around. Depending on their age, they may be able to do this step with supervision.
Take your tongs and grip one of the cans, so that your palm is facing up. Now quickly flip that can upside down and dunk it’s opening into an ice bath.
Instantly, everyone will hear a loud POP! And the can will crush inside itself. To figure out why, let’s dunk the other right side up.
Use your tongs to grab a hold of the other can, but this time instead of flipping it over and dunking it upside down, keep the can upright and dump it right side up into the other ice bath.
Nothing happened, right? No loud POP. No crushed can. It’ll just float there on top of the ice water. So what gives? Why the huge difference?
When we heated up our cans, we boiled the water inside them. When the water boiled, it turned into steam. When it turned into steam, it took up more space in the cans and pushed out most of the air. When it pushed out most of the air, it caused the air pressure inside the cans to be less than the pressure outside them.
Then when you placed the can upside-down in the ice bath, the steam rapidly turned back into water. Since water takes up less space than steam, and no air could enter into the can because the opening was submerged in water, the air outside the can exerted pressure on the can making it collapse! It may have even pulled some water up with it into the can!
The reason the same doesn’t occur with the other can is because air was allowed to enter in through the top of the can and equalize the air pressure.
It’s important to note we were placing extreme measures on our experiment. You don’t get the same crazy effect on your water bottle when driving down a mountain, because it’s much more gradual. But it does explain why you feel tightness in your chest when the air is colder.
Next time you're recycling aluminum cans, forget the can crusher, and use this experiment instead! Did we just make chores fun?
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