1. Measuring pressure

2. Aims
Describe the simple mercury barometer and its use in measuring atmospheric pressure
Use and describe the use of a manometer

3. The manometer
A manometer measures pressure difference.

4. Atmospheric pressure Gasses are also fluids
The atmosphere is made of gasses
The atmosphere exerts a pressure
Equal to
Density changes so must use average

5. Using atmospheric pressure

6. Pressure from the air

7. The mercury barometer Torricelli filled a tube with
mercury and inverted it into
an open container of mercury.
Air pressure Po acting on the
mercury in the dish can
support a column of
mercury 76 cm in height.

8. Standard atmospheric pressure
The pressure that will support a column
of mercury of mm heigh is known
as standard atmospheric pressure or
1 atmosphere (1 atm).
1 atm = 76 cmHg = x 105 Pa = 103 millibar (mb)

9. Pressure from the air
As the air is removed from the inside the external pressure crashes the can.

10. Uses of pressure in fluids

11. Hydraulic jack
The hydraulic press is an important application of Pascal’s Principle.

12. Hydraulic Brakes Brake pedal. Master cylinder. Break fluid.
Slave cylinder.
Large piston.
Brake disc.
Tyre.

13. Why are the walls of a dam wider at the bottom than at the top?
It is cheaper to build
Gravity increases with depth
Pressure increases with depth
Looks nice 

14. A pressure of 600 Pa acts over an area of 2m2
A pressure of 600 Pa acts over an area of 2m2. What force creates this pressure?
1 200 N
300 N
1 200 Pa
300 Pa 