For this model of barometer you need:
*a ruler, with tape attached for marking, or a piece of cardboard, or card stock
*a bit of polymer clay, or chewed chewing gum (we used the clay)
It's a pretty simple concept, if a little fussy to put together.
- Tape the straw inside the glass, so it doesn't quite touch the bottom of the glass.
- Fill the glass about halfway full of colored water.
- Suck some of the water into the straw (we chose to tip the glass, to fill the straw), then quickly plug the top of the straw with the clay, or gum, so the water stays in the straw.
- Tape the ruler, or card stock on the outside of the glass, next to the straw, and mark the level of the water in the straw, on the card stock.
Just like our other models, as the atmospheric pressures changes, the level of water in the straw will go up (for high pressure), or down (for low pressure).
All three models seem to be working about the same, going up and down together. In the comments of our second model, Brimful Curiosities asked if the water evaporation won't eventually lead to changing readings. I think it will, for that model, and this one.
And, although evaporation is not a problem with our first model, I think the balloon might lose some of its elasticity over time, changing the readings, too.
Still, for the short term, these homemade barometers have given the children a little better understanding of what atmospheric pressure is, and how measuring it, helps in predicting changes in the weather.
The Man of the House has suggested, that just one barometer on the kitchen counter might be sufficient. So, I think after today's readings we'll dismantle the two liquid filled barometers, to make room for our next project - a homemade thermometer!
It's great to be a homeschooler.