When the water in the can is heated, the molecules are
moving very fast and bumping into the walls a lot whichkeeps the can in its usual shape. When the can is capped
and cooled, the molecules aren’t moving as fast and can’t
keep the sides up. The molecules in the can aren’t bumping
into the sides very hard. (Spring 1997)
When the molecules inside the can are hot they are
farther apart or expanded. As the temperature in the can
decreases the molecules move closer together. The can’s
shape will change to accommodate the amount of space
needed. (Spring 1997)
The can’s walls would be sucked inward. The gas molecules
are moving around everywhere very quickly, bouncing off
of everything. When they do this, they exert a certain
pressure. Because the can is a closed system, the temperature
also changes but the pressure inside remains the same.
The pressure differences suck in the walls of the can.
(Spring 1997)
Another difficulty that was apparent in the responses is
that many of the students did not recognize the importance
of having the can filled with water vapor. In fact, 53 of the 70
students in the control group ignored the condensation of water
vapor, many attributing the decreased pressure inside the can
solely to the water molecules moving slower as the gas cooled.
While the can is being heated the gas particles are moving
really fast within the can, and some are coming out.
Then when you take the can off the heat and cap it, the
molecules are slowing down really quickly and the pressure
outside the can is greater than inside so the can will
compress. (Spring 1997)
When heated the H2O turns into water vapor—as this
cools, the gas takes up less space and since it is capped
and air can’t enter to even out the pressure on the inside
and out. The can must therefore collapse, because the
gas fill a small volume when cooled. (Spring 1997)
Although several student misconceptions were reported
above, 9 control group students gave a completely correct
response. For a response to be deemed completely correct, two
major points must have been mentioned: the condensation
of water vapor, which results in a lower inner pressure, and
the pressure differential between the lowered pressure inside
and the constant (atmospheric) pressure outside, which results
in the crushing of the can by the molecules outside the can.