The can crush experiment is a visually compelling science demonstration that showcases fundamental principles of physics. It illustrates how changes in temperature and pressure can lead to surprising physical phenomena.
Experiment Setup and Observation
To perform this experiment, gather an empty aluminum soda can, a small amount of water (about 15-30 milliliters or 1-2 tablespoons), a heat source like a stove or hot plate, a bowl large enough to submerge the can’s opening, cold water, and a pair of kitchen tongs. Pour the water into the can. Place the can on the heat source and allow the water inside to boil vigorously. Steam will rise from the can’s opening.
Once steam consistently escapes, use tongs to grasp the hot can near its bottom. Swiftly invert the can and plunge its opening into the bowl of cold water. The can will instantly implode with a loud “pop” sound. This collapse results from forces acting upon the can, which shift rapidly due to the temperature change.
Unpacking the Science
The core of the can crush experiment lies in atmospheric pressure, the force exerted on surfaces by the weight of the air above them. The Earth’s atmosphere constantly presses down on everything, including the aluminum can, with considerable force. At sea level, this pressure is approximately 14.7 pounds per square inch (psi) or 101.325 kilopascals (kPa).
When water inside the can is heated, it transforms into steam. This steam occupies a much larger volume than the liquid water it originated from, actively pushing most of the air out of the can. As the steam fills the can, the internal pressure becomes roughly equal to the external atmospheric pressure, preventing the can from collapsing.
The hot, steam-filled can is rapidly inverted into cold water. The sudden cooling causes the steam inside to condense almost instantly back into liquid water. Liquid water molecules take up significantly less space than steam molecules, leading to a drastic reduction in the number of gas molecules inside the can. This rapid condensation creates a partial vacuum, meaning the pressure inside the can drops sharply and becomes much lower than the external atmospheric pressure.
With the internal pressure greatly reduced, the external atmospheric pressure, previously balanced by the steam inside, becomes unopposed. This external force then pushes inward on the can from all sides, causing it to implode. The can collapses because the pressure difference between the outside and the inside exceeds the structural integrity of the aluminum.
Practical Tips and Related Concepts
When performing the can crush experiment, safety is a priority due to heat and hot materials. Always use kitchen tongs to handle the hot can, and consider wearing heat-resistant gloves. Children should only conduct this experiment under direct adult supervision to prevent burns from the hot can or steam. Ensure the cold water bath is ready and easily accessible for a quick transfer of the can from the heat source.
The experiment can be modified to observe different effects, such as varying the amount of water initially added to the can or using different temperatures for the cold water bath. These variations can influence the speed and extent of the can’s collapse.
The principle demonstrated in this experiment, involving pressure differentials, is evident in many everyday phenomena. Examples include how a straw works by creating lower pressure inside the straw, allowing atmospheric pressure to push liquid up. Similarly, suction cups adhere to surfaces due to the pressure difference between the inside of the cup and the outside air. Aircraft cabins are also pressurized to maintain comfortable breathing conditions at high altitudes, managing the pressure differential with the outside environment.