Siyapath
Sign up

Lesson: Chapter 15 — Fluid Pressure and Its Applications

15.4. Gas and atmospheric pressure 6 of 8

The aneroid barometer

There are also barometers that measure atmospheric pressure without using a liquid. They are called aneroid barometers.

Figure to be added

Figure 15.12 — an aneroid barometer; the evacuated chamber, the air pressure acting on it, the pointer it turns and the scale.

How it works

  1. It contains a chamber with thin metal walls, from which the air has been removed.
  2. When the outside pressure changes, the shape of the chamber's walls changes.
  3. A pointer turns according to that change in shape.
  4. A scale is provided for reading off the pressure.

The two kinds side by side

Point Mercury barometer Aneroid barometer
What it measures vertical height of a mercury column change of shape of the chamber walls
Liquid mercury is needed none at all
Portability awkward — about a metre tall easy — it is small

Mountaineers and aircraft use the aneroid barometer to measure altitude — since atmospheric pressure falls as you climb, the height can be read off from the pressure.