A few years ago, we launched a weather balloon during our summer science camp. The balloon reached an altitude of 30 km (100,000 ft)! Among other things, this project ended up being a great way to teach campers about the gas laws and how atmospheric pressure decreases with altitude.
The “bucket launch” is a fantastic experiment you can do if you have access to liquid nitrogen. Depending upon conditions, we have observed the bucket to launch anywhere from 80 to 160 feet high. See the video.
This demonstration shows the construction of of an eleven foot high barometer made with a concentrated solution of potassium tetraiodomercurate(II).
Comparing the densities of mercury, potassium tetraiodomercurate(II) solution, and water illustrates that barometers made from the three liquids have different heights.
The relationship between the volume of a gas and the pressure it exerts, known as Boyle's Law, is shown with a J-tube.
When water is squeezed into an inverted flask containing ammonia, the ammonia dissolves in the water and the reduced pressure causes a fountain effect.