Force in Fluid Systems

1. Force in Fluid Systems

2. 4 states of matter • Flip chart activity • Solid • Liquid • Gas • Plasma

3. Fluids • A fluid can be a liquid or a gas

4. Hydraulic Systems • A fluid system that uses a liquid as the fluid

5. Pneumatic • A fluid system that uses a gas as the fluid

6. Density See page 30 for the Density Table 1.4 • Density = mass / volume • Ex : 2 silver cubes

7. Rearranging EquationsDensity = mass / volume m D V D = m / V m = D V V = m / D

8. Table: Density Variable English SI • Density D lb-masskg yd3 m3 • Mass m lb-mass kg • Volume V yd3 m3

9. Density Ex: What is the density of an object that has a mass of 30 kg and a volume of 60 m3? • Density = mass / volume D = 30 kg / 60 m3 D = 0.5 kg/ m3

10. Volume • A Rectangular Object • Volume = length X width X height • m3, ft3 • Pressure Mathlab

11. Water • Density of water = 1 g / cm3 • Water Weight Density = 62.4 lb / ft3 • Hydrometer – an instrument that measures density

12. Specific gravity = density of a substance / density of water There is no unit Ex: Density of lead is 11.34 g/cm3 Specific gravity of lead is 11.34

13. Table: Specific Gravity Variable English SI • Specific gravity gsp none none • Density of a Ds lb/ ft3 g/cm3 Substance • Density of water Dw lb/ ft3 g/cm3

15. The Tale of Archimedes Problem: Did the goldsmith steal some of the gold that was to be used in the Crown?????

16. The King was sure some of his gold was stolen. • If Archimedes did not discover the answer Archimedes would pay with his life.

17. Buoyant Force • This is an upward force on an object that’s equal to the weight of the fluid displaced determining whether an object sinks or floats

18. Density and Buoyancy • If you are putting solids in water (1g/ml), if the density is: • 1 g/ml or less float • 1 g/ml or more sink • Apply this pattern to other liquids • Density/buoyancy Activity • Specific Gravity Mathlab

20. Pressure • Pressure = Force / Area

21. AREA • Area = length X width • m2, ft2

22. Table: Pressure Variable English SI Pressure P Psi N/ m2 Force F lb N Area A in2 m2

23. Pressure Example A woman has stiletto heels on she weighs 120 lb and the heel is 0.5 “ X 0.5”. How much pressure would the heal exert if all the woman’s weight is on one heel? Area= 0.5” X 0.5” = 0.25 in2 P = F / A = 120 lb / 0.25 in2 = 480 psi ( psi= lb/ in2) More than enough to puncture skin or the aluminum of an airplane

24. Pascal’s Principle • A change in pressure at any point in a confined fluid is transmitted undiminished throughout the fluid ex: barometer

25. Total Pressure = gage pressure + atmospheric pressure atmospheric pressure- many units 30 inches of mercury OR 14.7 psi

26. Table: Total Pressure Variable English English Total pressure P tot psi inches Gage pressure P g psi inches Atmospheric P atm 14.7 psi 30 in Pressure

27. Total Pressure Example A car tire needs a gage pressure of 30psi. What would be the total pressure on the tire? Total pressure = gage pressure + atmospheric pressure Atm press= 14.7 psi Tot press= 30 psi + 14.7 psi = 44.7 psi

28. Fluid Height Pressure = water weight density X height This can be used for any substance as long as you know the weight density

29. Fluid Height variable English SI Pressure P lb/ft2 kg/m2 Water wgt rw62.4lb/ft3 1000 kg/m3 Density Fluid height h ft m

30. Pressure in Tanks • The tank with the greatest fluid height has the greatest pressure (figure 1.26 pg 42) • If two tanks have the same height but different diameter the pressure at the bottom is the same (figure 1.28 pg 43) • Even if the tank funnels down to a small bottom surface, the pressure remains the same for thesame depthof fluid

31. Pressure in Tanks

32. Fluid Height Example A water tower is 300 ft high. What should the water pressure gage read at the bottom of the tower? Pressure = water weight density X height Pressure = 62.4lb/ft3 X 300ft Pressure = 18,720 lb / ft2