# How to crush a can using air pressure

You can compress a soda can with just a heat source and a bowl of water. This is a great visual demonstration of some simple scientific principles, for example air pressure and the concept of vacuum. The experiment can be done by teachers as a demonstration or by older students under supervision.

## Steps

### Part 1 of 3: Compress a can of soda

#### Step 1. Pour some water into an empty soda can

Rinse the can with water and leave about 1 to 2 tablespoons (15 to 30 ml) of water at the bottom. If you don't have a measuring spoon, pour in just enough water to cover the bottom of the can.

#### Step 2. Make a bowl of ice water

Fill a bowl with ice and cold water or with water that you have stored in a cold refrigerator. By using a bowl deep enough to hold the can, you can make the experiment easier to do, but it isn't necessary. A clear bowl will make it easier to see how the can is compressed.

#### Step 3. Get splash proof glasses and tweezers

In this experiment you will have to heat the soda can until the water inside boils, then you will have to move it quickly. All bystanders should wear splash proof goggles in case hot water splashes into their eyes. You will also need a pair of pliers to hold the hot can without burning yourself. Then you will place it face down in the bowl of ice water. Practice picking up the can with the tongs to make sure you can pick it up firmly.

#### Step 4. Place the can on the stove

Place the can upright on a stovetop, then set the heat setting to low. Let the water in the can boil, bubble and steam for 30 seconds.

• If you smell something funny or metal, move on to the next part right away. The water could have evaporated or the heat could have been very high, causing the ink or aluminum in the can to melt.
• If the stovetop cannot hold the soda can, use a hot plate or tongs with heat-resistant handles to keep it on the stove.

#### Step 5. Use the tongs to turn the hot can into the cold water

Hold the tweezers palm up. Use the tongs to pick up the can, then quickly flip it over the top of the cold water bath, plunging the can into the bowl of water.

### Part 2 of 3: How it works

#### Step 1. Learn about air pressure

The air around you is pressed against you and all other objects, with a pressure of up to 101 kPa (94.84 per cm2) when you are at sea level. This should normally be enough for a can to compress by itself or even a person. This does not happen because the air inside the soda can (or the material inside your body) pushes out with the same pressure and because the air pressure "cancels itself out", thus pushing us from all directions. equally.

#### Step 2. Find out what happens when you heat the can of water

When the water in the can boils, you can see that the water begins to escape as small drops in the air or vapor. Some of the air in the can is pushed out when this happens to make room for the expanding cloud of water droplets.

• Even though the can loses some air that's inside, you still won't get it to compress as the water vapor that took the place of the air will push in from the inside.
• In general, the hotter a liquid or gas, the more it will expand. If it is a closed container, it will not be able to expand further and will exert more pressure.

#### Step 3. Understand how a can is compressed

When you flip the can in the ice water, the situation changes in two ways. First, the can will no longer be open to air as the water will block the opening. Second, the water vapor inside the can will quickly cool down again. The water vapor will once again be reduced to its original volume, the small amount of water at the bottom of the can. Suddenly, most of the space inside the can will have nothing, not even air. The air that has been pressing from the outside of the can all this time will suddenly have nothing on the other side to resist it, therefore the can will be compressed inward.

• The space that has nothing is called empty.

#### Step 4. Look at the can closely to discover one more effect of the experiment

The appearance of the void or the space where there is nothing inside the can has another effect besides causing the can to compress. Watch the can carefully as you go down into the water and again as you lift it up. You may also notice that a small amount will be sucked into the can and then drip off again. This is because the pressure of the water will be pressed against the opening of the can, however it will be just enough to fill the can a bit before the aluminum is compressed.

### Part 3 of 3: Helping Students Learn Through an Experiment

#### Step 1. Ask the students why the can was compressed

See if the students have any ideas about what happened to the can. Do not affirm or deny any of the answers in this part. Accept all the ideas and ask the students to explain what they think.

#### Step 2. Help the students create variations on the experiment

Ask students to create new experiments to test their ideas and ask what they think will happen before they do the new experiment. If they have trouble creating a new experiment, help them. Here are some variations that may be useful to you:

• If a student thinks that the water (not the water vapor) inside the can was responsible for it being compressed, have the students fill a whole can with water and see if it is compressed.
• Try the same experiment with a sturdy container. Harder material should take longer to compress, which will give the ice water more time to fill.
• Try to let the can cool for a short time before you put it in the ice bath. This will result in more air in the can and therefore less severe compression.

#### Step 3. Explain the theory behind the experiment

Use the information in the "How It Works" section to teach your students why the can was compressed. Ask them if that matches what happened in the experiments.