||Building a Barometer
Air exerts pressure on Earths surface. In fact, it exerts pressure
in all directionsdown, up and sidewaysat the same time! At sea
level, air weighs 14.7 pounds per square inch. That means that a
desktop area 2 inches by 2 inches has almost 59 pounds of air sitting
over it. Standard copy paper (8.5 x 11 inches) has close to 1,375
pounds of air holding it down AND up at the same time.
- Empty coffee can
- large, heavy-duty latex balloon
- heavy rubber band
- coffee stirrer
- 3x5 card
- duct tape
- white glue
Read all Precautions before beginning this activity.
When you become accustomed to the way your barometer works, you will
have a tool with which to predict the weather. Determine how the
barometric pressure correlates to present weather.
- Smoothly tape the rim of the coffee can so the metal edge is
completely hidden but remains open. Be sure the tape smoothly extends
down the side of the can an inch or more. To effectively do this, tape
around upper side of the can leaving at least 1/2 inch of tape sticking
up over the rim. Use scissors to make 8 to 10 cuts in the protruding
tape straight down to the can rim. Fold the tape down and smoothly
stick it to the inside of the can.
- Cut the filler hole off the balloon and discard. Stretch the
balloon tightly over the taped edge and secure it with a rubber band.
Make the rubber band as tight as you can.
- Put a drop of white glue in the center of the stretched balloon.
Put the coffee stirrer on the glue and position it so that it protrudes
about 1/2 inch over the edge of the can.
- Tape the 3x5 card on the side of the can so that it extends over
the top and is close but not touching the coffee stirrer.
- Mark the card at the tip of the stirrer. It isnt necessary to put
- Write the current barometric pressure in a journal. Determine if
the pressure is high, low or somewhere in between. This will be your
baseline pressure. Be sure to note the position of the mark on the 3x5
card corresponding to the pressure.
- Repeat step 6 through several cycles of weather. Be sure you have
several highs and lows marked on your card and that you have entered
all information in your journal.
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