Rocket stretches plastic wrap tight over a jar and snaps a rubber band around it. "A drum," he says.
"A barometer," Nova corrects gently. "Once you add a pointer."
Raven tapes a straw flat across the wrap, one end at the center, the other sticking out past the rim.
Behind the straw she stands a folded index card and marks where the tip points.
"What do you notice?" she asks. "The air inside is sealed. The air outside can change."
"So if the outside air pushes harder, the wrap dips and the straw tip rises," Rocket says.
"Mark it every day at the same time," Nova says. "Then compare the marks with the sky."
You will build a simple aneroid barometer, the kind described in a National Weather Service learning lesson.
In your barometer, the jar is the sealed cell, the plastic wrap is its flexible top and the straw is the pointer.
Then you will mark the straw's level at the same time each day and watch for rising and falling.
The National Weather Service explains how it works. When the barometer is built, the pressure inside and outside is the same.
As air pressure rises outside, it pushes the plastic wrap down into the jar, and the straw tip rises.
When low pressure arrives, the pressure on top of the wrap drops. The wrap rises and the straw tip lowers.
Scientists at the University Corporation for Atmospheric Research add a warning: heating air raises its pressure. Keep your jar at a steady temperature.
| Day | Straw tip: higher, lower or same? | Sky | Wind |
|---|---|---|---|
| Day 1 | first mark | ||
| Day 2 | |||
| Day 3 | |||
| Day 4 | |||
| Day 5 |
| What the lab shows | True or false? |
|---|---|
| Your jar barometer is a simple aneroid barometer. | ? |
| Marks taken at different times each day are just as easy to compare. | ? |
| Rising outside pressure pushes the wrap down into the jar. | ? |
| The jar should sit in direct sun so the reading is bright and clear. | ? |
Your third instrument is built. Tomorrow you read what the National Weather Service says highs and lows bring.