Those friendly folks on the weather broadcasts often talk about how high- and low-pressure systems affect the daily forecast. This simple gizmo lets kids observe changes in air (or barometric) pressure and make some weather predictions of their own.
Set the barometer against a wall, out of direct sun, where it won't be disturbed. Place a chalkboard or a sheet of paper behind it. Mark a line where the arrow is level, then mark a few lines above and below it. Add labels as shown.
The air pressure inside the jar stays constant, while the outer barometric pressure changes.
When barometric pressure falls, the higher pressure inside the jar makes the balloon bulge and the arrow drop. Unsettled weather is approaching.
When barometric pressure rises, the lower pressure inside the jar causes the balloon to sink and the arrow to rise. Fair weather is on its way!
Originally published in the June/July 2013 issue of FamilyFun magazine.