Q&A for How to Make a Simple Weather Barometer

The balloon forms a seal around the jar, containing the air inside. At the time of sealing, the pressure inside the jar is equal to the air pressure - the straw is therefore level. When the air pressure increases, gas molecules push harder against the balloon from outside than inside, and the balloon is pushed downwards. As a result, the straw pivots upwards. When there is low air pressure, the opposite is true - the gas molecules inside the jar push harder against the balloon than outside, and the balloon is pushed upwards.

A barometer can only measure air pressure, giving an indication of the expected weather during the following 24 hours. Simply put, high pressure is likely to drive rain bearing clouds away, low pressure will likely let it in, leading to precipitation (rain).

Yes, it is very important to leave the barometer outside so that it can record more effectively.

No. If you tape the straw too hard, it might not move the way it's supposed to; taping it too loosely, though, could cause it to fall off. You need to find the perfect balance.

No, you can use another long, lightweight needle.

It depends on where it is outside, and how much it gets knocked around.

To stretch it out. If you just pull the two ends, you can rip it and you will have to get a new.

It is still just as effective, but it will tell you the air pressure indoors, not the air pressure outside.

It depends on where you put it, and how windy the weather is.

Long enough for the weather to change. Generally, it should always be outside as it is a weather instrument.

This all depends on the model and the maintenance it gets; if it’s a water barometer you need to make sure you keep adding water to prevent it all from evaporating.

The tubing acts like a straw. The straw must be clear or see-through. Remember to attach the straw to the ruler, and keep the top/mouth out of the water, at least peeking out of the bottle.

No, it should be on your porch or on your stairs or in your driveway, if it's safe there. It shouldn't be in the shade because it isn't going to work as well as it needs to.

The simple answer: your calibration is "automatic." It is done for you when you first make the barometer. In the air barometer, where the straw/needle is, that is your "initial" level. Then, as the air pressure changes, it will move up or down towards the "high" or "low" marks.

Put it somewhere in the shade, this wil prevent the sun from directly melting the balloon.

Yes, you do. It helps seal the jar to stop the air pressure from falling.

The stiffer the jar, the better. If it's a thin plastic, then it will flex with the balloon and make the straw move less, which is harder to read. But a really thick plastic might work.

No. This system relies on the expanding gas molecules inside of the balloon to record the pressure.

You should use a light-weight and long object. You can use a pen refill, thin cane, or even a straightened paper clip.

A glass jar would be preferable as it will not bend and it's less likely to tip over, but a plastic cup will work too.

You need to refill it when it is almost empty. If you notice water is less than usual, refill it immediately to get more results.

This depends on whether you are building the first one or the second. The first doesn't need water yet the second does.

A drinking straw is used by creating a suction with your mouth this causes a decrease in air pressure on the inside of the straw.

Any type of glass jar will work. However the type shown might be a little easier. So, a pint sized mason jar should work just fine.

No. What a barometer measures is the weight on the ground of the air in Earth's atmosphere.

Yes. Barometric pressure does vary slightly with air temperature.