Air Pressure and the Collapsing Can

Complexity level:	6
Project cost ($):	10
Time required:	1 hour to prepare, 1 hour for experiment
Material availability:	Very easily found
Safety concerns:	This experiment involves a stove and boiling liquid inside a metal can. Use kitchen gloves when handling the hot can and work near the stove with someone experienced in handling hot cookware.

Hypothesis

The empty soda can having a lower internal air pressure, will collapse inwards due to the higher water pressure outside the can.

Overview

Air pressure

Air molecules have a certain mass and when these molecules collide with a surface, pressure is felt on that surface. The molecules in the air contain kinetic energy and are always moving. The moving molecules are always colliding with one another or onto other surfaces creating the phenomenon that we call pressure.

Let us say we have a sealed container containing air. If we increase the amount of air molecules in the container, the number of air molecules colliding with the inner walls of the container will increase and so will the air pressure. If the number of air molecules inside the container is reduced, the air molecules colliding with the inner walls of the container will also reduce along with the air pressure inside the container.

Another method of varying the air pressure inside the container is temperature. Increasing the temperature of the container will cause the molecules inside the container to have a greater amount of kinetic energy. This will make the molecules collide more frequently amongst themselves and on the inner surface of the container causing the air pressure inside to be greater. Cooling down the container will reduce the kinetic energy and also lessen the collisions within the inner walls of the container, causing the air pressure to fall.

Scientific Terms

Molecules, kinetic energy, air pressure

Materials

The materials required for this science fair project:

-    1 stove

-    1 empty soda can

-    1 packet of ice cubes

-    1 pail of water

-    1 pair of kitchen gloves

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Procedure

1.    For this experiment, the independent variable is the temperature or the air pressure of the can. The dependent variable is what happens to the can. This is determined by observing the can after it is placed in the cold water. The constants (control variables) are the temperature of the water, the temperature of the air inside the soda can and the volume of the soda can.

2.    About 2 cm   of water (fill-depth) is poured into the empty soda can and it is placed on the stove. Fire up the stove and let the water in the can boil for a few minutes. When the water in the can starts to boil, allow the steam to flow freely out of the can.

3.    Ice cubes are then put inside the pail of water to bring down its temperature.

4.    Once the water in the can has been boiled for a few minutes, the can is picked up using the hot pad gloves. Be careful not to touch the soda can with bare hands. The can is turned upside down and immediately immersed into the cold water.

5.    Observe and record what happens to the empty can once it is pushed into the pail of cold water.

Results

The can will be crushed-inwards, as soon as it is placed in the cold water.

Crushing can air pressure science fair project

Conclusion

The hypothesis that an empty soda can having a lower internal pressure will collapse inwards due to the higher exterior water pressure is proven to be true.

When the water in the soda can starts to boil, the air is pushed out (displaced) by the steam from the boiling water. The air space in the can is replaced by the steam. When the can is turned upside down and pushed into the cold water, the steam quickly cools and turns back into water droplets in an instant, creating a vacuum inside the can. The water pressure outside the can immediately starts to push against the walls of the soda can. This causes the walls of the soda can to collapse inwards.

Also consider

Try to repeat the experiment with different types of metal containers.

Try another experiment by capping an empty plastic bottle tightly and placing it in the freezer.

References

Atmospheric pressure - http://en.wikipedia.org/wiki/Atmospheric_pressure

Air pressure -http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/circulation/air_pressure_p_1.html

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