- You'll need these materials:
- a glass or beaker with straight sides
- a ruler (12 inch)
- one foot of clear plastic tubing
- a stick of chewing gum
|Begin by standing the ruler in the glass and
holding it against the side. Tape the ruler to the inside of
the glass. Make sure that the numbers on the ruler are visible.
|Stand the plastic tube against the ruler in
the glass. Make sure that the tube is not touching the
bottom of the glass by positioning the tube up a half inch
on the ruler. Secure the tube by taping it to the ruler.
|Chew the stick of gum so that it is soft.
While you're chewing, fill the glass about half way with
water. Use the plastic tube like a straw and draw some water
half way up the tube. Use your tongue to trap the water in
the tube. Quickly move the gum onto the top of the tube to seal it.
|Make a mark on the ruler to record where the water level is
in the tube. Each time you notice a change in the water
level, make another mark. You'll notice, over time, that the
water level rises and falls. Pay attention to the change in
weather as the water level changes.
|The water in the tube rises and falls because
of air pressure exerted on the water in the glass. As the
air presses down (increased atmospheric pressure) on the
water in the glass, more water is pushed into the tube,
causing the water level to rise. When the air pressure
decreases on the water in the glass, some of the water will
move down out of the tube, causing the water level to fall.
The change in barometric pressure will help you to forecast
the weather. Decreasing air pressure often indicates the approach
of a low pressure area, which often brings clouds and precipitation.
Increasing air pressure often means that a high pressure area
is approaching, bringing with it clearing or fair weather.