A bell jar with several
demonstrations is evacuated in class:
A balloon with a tiny amount
of air inflates.
A metal ball of air is
balanced with a mass (shown below). As the bell jar is evacuated, the
buoyant force decreases and the ball falls raising the mass.
A short mercury column with a
small air bubble falls.
A container of water boils at
room temperature. The water temperature as measured by a thermometer falls
rapidly.