1. Static Fluids
Fluid – any substance that takes the form of the container in which it is held. (gases and liquids)

2. Activating Question #1
Which weighs more? A bucket full of water or a bucket full of air? Explain.
Density = mass/volume

3. Finding the weight of a fluid
Weight = mg… but finding the mass of a fluid can be challenging.
Finding weight of a fluid…

4. Activating Question #2
Which exerts more force on the ground? A person standing on 1 foot? Or the same person standing on 2 feet?
Both exert the SAME force on the ground.
The person on 1 foot exerts more Pressure on the ground.
Pressure = Force/Area

5. Pressure
Since pressure depends on force and area, this is why a person can lay on a bed of nails relatively safely, but cannot lay on a single nail.
The area of a bed of nails is larger so the pressure is smaller on the body.
The area of a single nail head is small, so the pressure is large… ouch

6. Pressure due to a fluid Pressure = force/area
So.. Pressure = weight of fluid/area

7. Pressure due to a fluid
Absolute Pressure = Pressure due to the depth of the fluid and added to the atmospheric pressure on top of the fluid.
Absolute Pressure = P0+ρgh
Gauge Pressure = pressure just due to height of liquid
Gauge Pressure = ρgh

8. Activating Question #3
If I have a beaker of water on a scale, will the weight of the system change if I just touch the top of the water?
The weight of the water increases just by touching the water… why?
Pascal’s Principle: The pressure of a fluid acts equally in all directions.
The added pressure of touching the water on the top is also exerted on the bottom of the beaker and therefore increasing the weight.

9. Pascal’s Principle Mathematically
Pin = Pout
For Hydraulic Lifts, the ratio of F/A remains constant. So a little bit of force over a small input area, will cause a large force out if it is over a large area. (lifting a car on a hyraulic lift)

10. Buoyancy
Any object that is submerged in a fluid experiences a buoyancy force.
This is a force that pushes upwards on an object that is submerged in a fluid.
What does the amount of buoyant force on an object depend on?

11. Archimedes’ Principle
When an object with a volume, V, is placed in a fluid, it displaces a volume of V of the fluid. (a bathtub filled to the top, when you put your foot in, it overflows).
Archimedes’ Principle: The buoyant force on an object is equal to the weight of the fluid displaced.

12. Archimedes’ Principle Mathematically

13. Now the applications… Pressure Units…
Standard units are N/m2… also known as Pascals (Pa)
Atmospheres of pressure (Atm)
1 atm = 1x105 Pa
There’s also… Torr, bar, mm-Hg, mm-H20, PSI…

15. Barometers
Looking at the diagram, explain how a Torricelli barometer functions.

16. A glass tube is completely filled with Hg and then inverted into a bowl of Hg. If the tube is long enough, the level of the mercury will drop, leaving a vacuum at the top of the tube.
Some calculations…
P = ρgh = (13.6x103)(9.8)h = 1x105
h = 0.76m

17. Check for understanding
Calculate the height of the tube needed for a water barometer…

18. Suction Cups Describe how a suction cup functions.
Check for understanding: A NASA intern suggests using suction cup shoes for astronauts to walk along the outside of a spacecraft. Gently tell this intern what is wrong with his solution.

19. Water in a straw
When placing your finger over a straw that is submerged in water, the water stays in place when removed from the water… why?

21. Hydraulic Lifts

22. Airlocks
Mr. Roth’s airlock… how does it work?

23. Siphoning
How can we get the water in the bucket to the water in the sink using the plastic tubing?

24. Units for Density Standard units are kg/m3 CHECK FOR UNDERSTANDING:
Covert 1 g/cm3 into kg/m3

25. Coke vs. Diet coke submerged in water
Huh? Why?

26. Is the crown made of gold?
When a crown of 14.7kg is submerged in water, an accurate scale reads only 13.4kg. Is the crown made of gold?

27. Hydrometer
A hydrometer is a tool used by brewers to determine the relative density of their wort compared to water.

28. Check for understanding
A particular hydrometer is weighted at the bottom with a mass of 45.0g. It is 25.0cm long and has a cross-sectional area of 2.00 cm2. How far from the weighted end should the mark be placed?