It is possible to crush an aluminum can by simply using a heat source and a bowl of water. This experiment is nothing more than an effective practical demonstration of some simple scientific principles, such as air pressure and the physical concept of vacuum. The procedure can be performed by a teacher for demonstration purposes, but also by an experienced student under supervision.
Steps
Method 1 of 3: Crush an Aluminum Can
Step 1. Pour some water into an empty aluminum can
Rinse the can, leaving about 15-30ml (1-2 tablespoons) of water at the bottom. If you don't have a dispenser available, just pour in 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 placed in the refrigerator to cool. To make the experiment easier, it may be advisable, although not necessary, to use a bowl deep enough to hold the can. A clean bowl will also make it easier to observe the squeezing process of the can.
Step 3. Prepare a pair of splash goggles and tongs
During the experiment you will have to heat the aluminum can until the water inside it boils, and then move it quickly. Everyone present should wear a pair of splash goggles to protect themselves from any splashes of hot water. You will also need a pair of tongs to grab the hot can without burning yourself and turn it upside down in the bowl of ice water. Try grabbing the can with pliers to make sure you are able to lift it firmly.
Continue under adult supervision only
Step 4. Heat the can on the stove
Place the aluminum can upright on a stove over low heat. Bring the water to a boil and let it flow out of the can, bubbling and releasing the water vapor for about thirty seconds.
- If you smell a strange or metallic smell, immediately proceed to the next step. The water may have evaporated completely or the temperature may have been too high, causing the ink or aluminum in the can to melt.
- If your stove is unable to hold an aluminum can, you can use a griddle, or hold the can raised over the stove using a pair of heat-resistant handled pliers.
Step 5. Use tongs to flip the boiling can into the cold water
Hold the pliers with your palm facing up. Lift the can with tongs, then turn it upside down and dip it into the bowl with cold water.
Be prepared for the loud noise of the can crumpling quickly
Method 2 of 3: The Principle of Operation
Step 1. Find out how atmospheric pressure works
The air around you exerts a pressure equal to 101 kPa (14.7 pounds per square inch) at sea level on you and any other object. Such pressure alone would be enough to crush a can, or even a person! All this does not occur because the air present inside the aluminum can (or the material contained in your body) exerts a push towards the outside with the same pressure and because, moreover, the atmospheric pressure "vanishes", exerting an equivalent thrust from each direction.
Step 2. Imagine what happens when the can of water is heated
When the water contained in the can reaches boiling temperature, it will begin to evaporate in the form of small drops or water vapor. To make room for the expanding cloud of water droplets, some of the air inside the can will be pushed out.
- Even if it loses part of the air contained inside it, the can will not crush for the moment, since the water vapor that has taken the place of the air will in turn exert pressure from the inside.
- Generally speaking, the more a liquid or a gas heats up, the more it will tend to expand. If a closed container does not allow it to continue to expand, the contents will exert even more pressure.
Step 3. Understand why the can squeeze
When the can is turned upside down in ice water, its condition changes in two ways. Firstly, the passage of air inside the can is no longer possible, as its opening is blocked by water. Secondly, the water vapor contained inside the can begins to cool rapidly. The water vapor then returns to its original volume, i.e. the small amount of water initially present at the bottom of the can. The inside of the can suddenly becomes almost entirely empty, without even air! The air, which continues to exert pressure from the outside, suddenly finds nothing to resist from the opposite side and is therefore able to squeeze the can inwards.
A space with nothing in it is called empty.
Step 4. Look closely at the can to discover another aspect of the experiment
In addition to the crushing of the can itself, the appearance inside the can of a vacuum, that is, a space that contains nothing, also causes another effect. Watch the can carefully as you dip it into the water and lift it up. You may notice a small amount of water being sucked into it, then dripping out once more. This phenomenon is caused by the pressure of the water, which exerts a push against the opening of the can, but with such force as to be able to fill only part of it before the aluminum is crushed.
Method 3 of 3: Helping Students Learn from the Experiment
Step 1. Ask students to explain why the can is squeezed
Collect their views on what happened to the can. For the moment, do not confirm or deny any of the responses received. Accept each theory and ask students to justify their reasoning.
Step 2. Help the students work out some variations of the experiment
Ask them to devise new experiments to test their ideas, and ask them what they think will happen before carrying out the new experiment. If they have trouble developing one, help them. Here are a couple of variations that might help:
- If a student thinks that the water (not the water vapor) contained inside the can is responsible for the squeezing, have the students fill a whole can with water to check if it is squeezed or not.
- Do the same experiment with a sturdier container. A heavier material will take longer to squeeze, thus giving the frozen water more time to fill the container.
- Allow the can to cool for a short time before plunging it into ice water. There will be more air inside the can, thus leading to less drastic squeezing.
Step 3. Explain the theory on which the experiment is based
Use the information in the Principle of Operation section to explain to students why the can is crumpled. Ask them if this explanation matches what they had imagined in the course of their experiments.
Advice
Gradually dip the can into the water with the help of the pair of tongs, instead of dropping it
Warnings
- The can and the water inside will be hot. Make sure attendees stay away when dipping the can, to prevent anyone from getting injured by any splashes of boiling water.
- Older kids (ages 12 and up) may be able to perform this experiment on their own, but always under adult supervision. Do not allow it to be performed by multiple people at the same time, unless there are multiple supervisors present.
