1. Fluids

2. Definition
Has no fixed shape
Ability to flow

3. Density (ρ) Mass per unit volume ρ = m/V SI unit – kg/m3
Specific to different materials (pg. 301)
What is the mass of a solid iron wrecking ball of radius 18cm?

4. Specific Gravity
Ratio of density of a substance to the density of water (1000 kg/m3)
What is the specific gravity of whole blood?

5. Pressure Force per unit area: P = F/A Unit N/m2 = pascal (Pa)
Fluids exert pressure in all directions
Pressure due to liquid at any depth, h, is due to the weight of the liquid above it

6. Equation F = mg m = ρV V = Ah F = ρAhg P = F / A P = ρAhg/A
P = ρhg (for liquids)
Called Gauge Pressure

7. Pressure is directly proportional to density and depth
Pressure at equal depths in the same liquids is the same

8. At the same height, which experiences a greater water pressure at the bottom?

9. Example
The surface of a water storage tank is 30m above the faucet in the kitchen. Calculate the water gauge pressure in the faucet.

10. Atmospheric Pressure Unit – atmosphere (atm) 1atm = 101.3 kPa
If the surface of a liquid is open, the total pressure is the sum of the atmospheric and gauge pressures
P = Pa + ρgh

11. Example
What is the total pressure on a scuba diver in a lake at a depth of 8.00? (standard atmospheric pressure)

12. Pascal’s Principle
Pressure applied to a confined fluid increases the pressure throughout by the same amount
Pout = Pin
F1 = F2
A A2

13. Small force over small area is the same as a large force over a large area - Hydraulics

14. Example
The area of the output piston is 20x that of the input cylinder. What force would need to be applied to lift a 1800kg car?

15. Buoyancy Upward net force on objects within a liquid
Occurs because pressure in a fluid increases with depth
Since the bottom is deeper, more force is pushing up than force on the bottom pushing down
Net upward force pushes objects up

18. Archimedes Principle
Weight of fluid displaced is equal to the volume of the object

19. FB = ρfluidgVsubmerged

20. Example
A 70kg statue lies at the bottom of the sea. Its volume is 3.0 x 10-2 m3. How much force is needed to lift it?
When a crown of mass 14.7kg is submerged in water, an accurate scale reads only 13.4kg. Is the crown gold?