How To Make a Barometer.

A Barometer is used to measure the atmospheric pressure and is a tool to forecast the weather. (5/06/2007)


What is a "Barometer" ?


Answer: An instrument used to measure atmospheric pressure. There are two main types: aneroid and mercury. The aneroid barometer makes use of a small sealed chamber connected to a pointer mechanism. Mercury barometers use a glass tube filled with mercury and inverted over a mercury-filled chamber. Normally, the atmosphere at sea level can support the column of mercury to 29.92 inches. An aneroid barometer is calibrated so that its pointer reads the pressure as inches of mercury, too.


I don't have lots or mercury (only on my teeth fillings as my dentist said, but is not enough to make one), so I decided to build this "Aneroid Barometer"


Here is what I need:


1 Empty tuna can, cup or anything wide that can hold water.
1 12" Baloon (Doesn't matter if helium grade)
1 Rubber band
1 Any of this available: Chopstick, bambu stick or straw. Anything longer than 8" work fine.
1 Piece of cardboard, marker or pen.
  Glue (or tape) and Scissors.


**WARNING*** - Rubber balloons, ruber bands and scissors are dangerous! I'm not kidding, you can hurt yourself if those items are not used properly. Read the disclaimer at the main page.


cut the balloon. Cut the balloon as the photo show.


put the balloon on the cup Put the balloon on the cup, fix the ruber band so the balloon doesn't slip off.


glue the chopstick Glue the bamboo stick (or straw) at the center of the baloon. If the stick is heavy and the can or cup flips over, put some water on it.


make the cardboard meter Use the card board and tape to make it to stand vertically.


measure the pressure. After the glue is dry, use the cardboard to put some marks and measure the pressure. If the weather is cloudy or raining, put the middle mark above the stick. If the weather is sunny, put the middle mark below it.


cloudy day Your barometer should be ready. When I built it, I had rain, so the stick was pointing just below the middle line.


weather going better After 20 minutes, the "needle" moved.


Low pressure is associated with less stable weather patterns, while high pressure is associated with more stable weather patterns. To forecast weather with your barometer, it is important to watch the speed and direction of barometric change.


On this case, the needle was going up, that means, the weather will improve.


Basically, here is how to read the barometer:



High Pressure:
Rising or steady - Continued fair
Slowing falling - Fair
Rapidly falling - Cloudy, Warmer


Medium pressure:
Rising or steady - Same as present
Slowing falling - Little change
Rapidly falling - Precipitation likely


Low Pressure:
Rising or steady - Clearing, cooler
Slowing falling - Precipitation
Rapid falling - Storm


How it works?


The air inside the cup have a different presure than the outside air, so it makes the balloon to bend outside or inside. If the atmospheric pressure is low, the pressure inside the cup will be higher and it pushes the balloon outside and the stick will point to a lower level.


When the atmospheric pressure is high, the pressure inside will be lower and the stick will point higher.


This is not a "professional" barometer but works fine, excellent for a science project or just for fun.


5/6/07 Update: At night, the pressure was high. That indicates we will have better weather the next morning. The weather channel forecast shows a sunny morning. My barometer works like a charm.


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