Pressure and Pascal’s Principle

PRESSURE!

FORCE

Pressure – force per unit area

FP

A

2Units:

NPa

m

Quick lab.Find the pressure each of your feet

exerts on the floor.

How would the pressure change if you stood on one foot?

How would the pressure change if your weight doubled?

Pascal’s Principle

Any change in pressure applied to a completely enclosed fluid is transmitted undiminished to all parts of the fluid and the enclosing walls

1 21 2

1 2

F FP P

A A 2

2 11

AF F

A

2

21 1

1 2 2 22 2

20500F N

A rF F F

A r

2

1 2

(0.0120)20500 131( )

(0.150)F N

Compare work??? Compare distance traveled by each piston?

Download Pascal worksheet from the website

Practical use:A bottle of juice is sealed under partial vacuum, with a lid on which the red dot or “button” is painted. Around the button the following phrase is printed: “Button pops up when seal is broken”. Explain why the button remains pushed down when the seal is intact.

Download gauge pressure worksheet from the website

Gauge Pressure

F mg Vg gAhP gh

A A A A

Absolute pressure (including atmospheric)

oP P gh

Pressure in a fluid at the depth h

What is the sub-atmospheric pressure in Pa and atm if the height of the Hg column in the barometer is 690 mm?

If the tube were doubled in diameter, what would happen to the height of the column?

How tall should a barometer be to measure normal atmospheric pressure if instead of Hg it is filled with water?