You can crush a soda can with just a heat source and a bowl of water. This is a visual demonstration of some simple science principles, including the pressure of water and the concept of a vacuum. These experiments can be carried out by the teacher as a demonstration or by senior students under supervision.
Step
Part 1 of 3: Crushing Soda Cans
Step 1. Pour some water into an empty soda can
Rinse the soda can with water and leave about 15-30 mL (1-2 tablespoons) of water in the can. If you don't have a tablespoon, just pour enough water to cover the bottom of the can.
Step 2. Prepare a bowl of ice water
Fill a bowl with cold water and ice or with water that has been chilled in the refrigerator. A bowl deep enough to submerge the can will make the experiment easier but not mandatory. A clean bowl will make it easier for you to see the can crumble.
Step 3. Take splash-proof glasses and clamps
In this experiment, you'll heat this can of soda until the water in it boils, then quickly transfer it. Everyone nearby had to wear splash-proof goggles in case the hot water splashed in their eyes. You'll also need tongs to pick up the hot can without burning yourself, then flip it over in a bowl of iced water. Practice picking up cans with tongs so you're sure you can pick them up firmly.
Proceed only with adult supervision
Step 4. Heat the can on the stove
Place the can of soda right over the stove, then turn the heat setting to low. Let the water boil outside the can, bubbly, and let off steam for about 30 minutes.
- If you smell something strange or metallic, move on to the next section immediately. The water may be boiling or the heat is too high, causing the ink or aluminum in the can to melt.
- If your stove can't heat the soda can, use a hot plate, or use tongs with heat-resistant handles to hold the soda can on the stove.
Step 5. Use tongs to flip the hot can in the cold water
Hold the clamp with your palm facing up. Use the tongs to pick up the can, then quickly flip it over the cold water, dipping the can into the bowl of water.
Get ready for a loud bang as the can shatters quickly
Part 2 of 3: How it Works
Step 1. Learn about air pressure
The air around you compresses you and everything else, with a pressure of 101 kPa (14.7 pounds per square inch) when you are at sea level. This pressure is usually enough to shatter a can, or even a person! This doesn't happen because the air in the soda can (or any other substance in your body) pushes out with the same amount of pressure, and because the air pressure dissipates it by pressing on us in all directions equally.
Step 2. Find out what happens when you heat a can of water
When the water in the can boils, you can see the water starting to leave the can as water droplets in the air, or steam. Some of the air in the can is pushed out as it boils, to make room for the expanding water droplets.
- Even though the can had lost the air inside, it had not crumbled, as the moisture present in the air was pressing down from within.
- Generally, the more you heat a liquid or gas, the more it expands. If it's in a closed container so it doesn't expand, the liquid or gas compresses even more.
Step 3. Understand the process of crushing cans
When the can is turned over in iced water, the situation changes in two ways. First, the can is no longer in contact with air because water is blocking the opening. Second, the moisture in the can can cool quickly. The water vapor once again shrinks to its initial volume, becoming the amount of water at the bottom of the can. Suddenly, the room became empty – not even air! The air that had been pressing from the outside of the can suddenly had no pressure from the inside, thus destroying the inside.
A space that has nothing in it is called the vacuum.
Step 4. Look closely at the can for other effects of this experiment
The appearance of a vacuum or empty space in the can has one effect other than causing the can to shatter. Watch the can carefully as you submerge it in the water, and then lift it up. You may notice that some water gets into the can and then drips out again. This is because the pressure of the water presses against the holes in the can, but little can fill the can before the aluminum disintegrates.
Part 3 of 3: Helping Students Learn from Experiments
Step 1. Ask students why the can was crushed
Notice if students have any ideas about what happened to the can. Don't agree with or blame their answers at this stage. Accept each idea and ask students to explain their thought processes.
Step 2. Help students to think of variations in the experiment
Ask students to do new experiments to test their ideas, and ask them what they think will happen before they do the new experiment. If they can't think of a new experiment, help them out. Here are some variations that may be useful:
- If a student thinks that the water (not moisture) in the can is the reason the can shatters, let the student fill the entire can with water, and watch if the can shatters.
- Try the same experiment with a stronger container. Stronger materials will take longer to disintegrate, which will give the ice water more time to fill the can.
- Try to cool the can for a while before putting it in the ice water. This will cause more air to be contained in the can so that the crushing is less severe.
Step 3. Explain the theory behind this experiment
Use the information in the How it Works section to teach students why cans shatter. Ask them if this information fits the idea they came up with during the experiment.
Tips
Submerge the can in the water using tongs, and don't drop it
Warning
- The can and the water in it will be hot. Have the audience back off while the can is turned over in the water, to avoid getting hurt from hot splashes.
- Older children (aged 12+) can do this alone, but only under adult supervision! Never allow more than one person to demonstrate unless more than one supervisor is present.
