1. Pressure of a fluid or gas
Atmospheric pressure: lbs/in2= 1.013x105 N/m2 or Pa
Demo: lungs, can

2. Density r­air = 1.29 kg/m3 r­water = 1000 kg/m3
r­mercury = kg/m3
Weight of an object with density r, in terms of dimensions.

3. Pressure vs depth in a static fluid
Comes from the weight of water (and air) above some area A at depth h

4. Pascal’s principle: For a fluid at rest, the pressure in the fluid depends only on the depth, not the shape of the container.
Hydraulic systems and force amplification

5. Hydraulic systems and force amplification
Do the pistons move the same distance during the lifting?

6. Manometers

7. Straws and pumps: lifting fluids
How high can we “pull” water with a vacuum?
How do you get water from a very deep well?

8. Lifting fluids Barometers
How high can we “pull” mercury with a vacuum?
Barometers

9. P1. For a longer canyon behind the dam (red arrow length), the dam ____________ a) can be weaker b) must be stronger c) can be the same.

10. P2. On the moon, where gravity is less, and there is no atmosphere, if you pumped out the air at the top of a barometer, the mercury would rise ________ compared to on earth.
higher
less high
the same
not at all

11. Bouyancy: higher pressure on bottom of object…it’s deeper.

12. Bouyancy: water displaced moves upward … it “wants” to fall back down (to lower potential energy)

13. Archimedes’ principle
The buoyant force is the weight of the fluid that the object is displacing

14. Floating vs sinking Competition between upward and downward forces
Comes down to density of object vs density of the fluid

15. Floating objects rise out of the water until:
Submarines and fish can adjust their density!

16. Two cubes of the same size made of steel and wood are placed in water
Two cubes of the same size made of steel and wood are placed in water. The wood floats (some is above the water), and the steel sinks. After they come to rest,
P3. the bouyant force is greatest on which block?
steel
wood
none…same

17. A block of wood of size 0. 5m x 8m x 2m has density 250kg/m3
A block of wood of size 0.5m x 8m x 2m has density 250kg/m3. It is held all the way under the water with a chain. Draw a FBD of the block Find the buoyant force and the tension in the chain

18. A 200-ton ship enters the lock of a canal
A 200-ton ship enters the lock of a canal. The fit between the sides of the lock and the ship is tight so that the weight of the water left in the lock after it closes is much less than 200 tons. Can the ship float?