Make your own barometer!
I love the weather. I’ve already talked about my favourite weather signs, now what about something a tad more scientific. How about a barometer? Making one is really, really easy and I’m going to show your how. The kind I’m going to show you is called a weather glass. You can find them in home and garden catalogs, but come on, let’s just make one instead!
Before I get into the make, let’s talk about what barometers do. Barometer’s measure the minute changes in atmospheric pressure that indicate changes in weather. Minute? Yeah, really, really small. Okay low pressure (usually associated with rain) is about 29 milibars, high pressure (nice weather) is about 30. One freakin’ millibar that’s it! Barometers used to be all done with liquids, because they are prevalent and easy to deal with. How? Simple, it’s all PV=nRT. Universal gas law. With temperature relatively constant, changes in pressure will change the volume. Uh huh. Okay, here’s what’s going on.
The bottle is filled with water almost to the top and closed. At the bottom I’ve cut a small hole and used silicone caulk to seal a narrow plastic tube in. I used a little more caulk to stick the tube to the bottle. Okay, note in the picture that the opening of the tube is well below the top of the water. This is really important. So as the pressure from the air pushes down on the narrow opening it changes the water level. Higher pressure, lower level in the tube, lower pressure, higher in the tube. As you can see the water is at the top of the tube and when I took the picture … it was raining. In fact, the tube is nearly overflowing right now. As the storm clear, high pressure will take over and push the water back down.
Now, as low pressure heralds a coming storm, you watch your weather glass for when it rises more than when it falls. You want to know when it’s going to rain, you can tell when it’s clearing up.
So making it … I described it above, it’s really that simple.
Here’s exactly what I used. Some things I figured out. The bottle needs to be almost full so that the tube will be the sensitive part, not the air above the water. Too much air and the tube level will not change. Also keep the bottle out of the sun. Why? Temperature. If the bottle warms and cools it will be temperature not pressure making the water level rise (the increased temp will increase the volume of the water making it go up).
It will take about 5 mins to make this, about 30 mins to dry enough to fill, and a day to get things acclimated to be able to predict the weather. Except for the cutting the hole part, very kid friendly project. Yes, I would also put food colouring in the water to make it easier to see.
This first one was the prototype. The next one I’m going to make will be for my daughter’s class. They’re studying weather, don’t ya know.
October 12th, 2006 at 1:47 pm
[…] Remember my homemade barometer? Come on I just wrote about it on Monday ! Seriously here’s a little update for you. First, as you can see, I’ve coloured the water to make it easier to see. The water level in the tube isn’t accurate. I quickly opened and closed the top to fill the tube a bit for the picture. […]
January 20th, 2007 at 11:20 am
hey tris, how would you know, let’s say if the water level in the tube is low, if it’s warm “right now” or it’s “going to be warm”?
January 20th, 2007 at 11:24 am
It means that it’s high pressure and good weather and should stay that way for a bit.