1. Manometers and Barometers
Instruments Used to Measure Pressure

2. Manometers
A manometer is comprised of a bulb containing a gas and a U-shaped tube.
The U-shaped tube is partially filled with mercury.

3. Manometers
Depending on the pressure of the contained gas, the mercury shifts.
The difference between the heights of the mercury on each side of the tube is a measure of the pressure of the gas.

4. Manometers
When gas pressure is greater than atmospheric pressure, the mercury is pushed toward the open end.
When gas pressure is less than atmospheric pressure, the mercury is pushed toward the gas reservoir.
What is doing the “pushing?”

5. Barometers
A barometer consists of a tube filled with mercury that is placed, upside-down, in an open dish of mercury.
The top of the tube is a vacuum.
The bottom of the tube is open to the atmosphere.

6. Barometers
There is a reservoir of mercury at the bottom of each barometer.
Depending on the atmospheric pressure, the level of fluid in the barometer can RISE or FALL.
The weather report may say, “The pressure is inches and falling.”
What do you think this means?