11 Other Densities Platinum Diamond Chromium Tin (white) Tin (gray) 21.45 3/25/2017PlatinumDiamondChromiumTin (white)Tin (gray)21.457.157.2655.769
12 What is the mass in grams of mercury with a volume of 1cm3? 3/25/2017DensityWhat is the mass in grams of mercury with a volume of 1cm3?D = m / v13.6 g/cm3 = x / 1cm313.6 g = x
13 What is the mass in kilograms of balsa wood with a volume of 1m3? 3/25/2017DensityWhat is the mass in kilograms of balsa wood with a volume of 1m3?1m3 = __cm31m3 = 100cm x 100cm x 100cm= 1,000,000 cm3D = m / v.3g / cm3 = x / 1m3.3g / cm3 = x / 1,000,000cm3300,000 g = x300 kg =x
14 Density of a substance divided by the density of water 3/25/2017Specific GravityDensity of a substance divided by the density of waterBecause specific gravity is density/density the units cancel out and is written as a whole number
15 Specific Gravity Copper has a density of 8.9g/cm3 3/25/2017Specific GravityCopper has a density of 8.9g/cm3What is its specific gravity?Specific Gravity = density of substance= density of waterS.G. = (8.9g/cm3) / (1.0g/cm3)S.G. = 8.9
19 3/25/2017HydrometerInstrument that measures density or specific gravity of fluidsCan you drown in quick sand?
20 Force per unit area exerted by a fluid 3/25/2017PressureForce per unit area exerted by a fluid
21 Force on Airplane Windows 3/25/2017Force on Airplane WindowsAn airplane window has a surface area of 136 square inches.Air pressure inside the cabin is 12.3 lb/in2Find:The force pushing on the window
22 What happens to the pressure as we move away from the earth? 3/25/2017PressureWhat happens to the pressure as we move away from the earth?
23 Force on Airplane Windows 3/25/2017Force on Airplane WindowsAn airplane window has a surface area of 144 square inches.Air pressure inside the cabin is 14.7 lb/in2Air pressure outside the window is 6.7 lb/in2Find:The force pushing in the windowThe force pushing out the windowNet force on window
24 Outward force on window 3/25/2017Inward force on windowF = P x AF = (6.7 lb/in2)(144in2)F= 964.8lbOutward force on windowF = P x AF = (14.7lb/in2)(144in2)F = lb
25 Net Force on window Net Force = Force out – Force in 3/25/2017Net Force on windowNet Force = Force out – Force inNet Force = lb – lbNet Force = 1152 lbThe window is being pushed outward with a net force of 1152 lb.
26 3/25/2017Net Force on windowIf the plane rises to a higher altitude and the pressure outside the plane changes to 5.4 lb/in2How much stronger will the windows need to be in order to hold the pressure
27 Outward force on window 3/25/2017F = P x AF = (14.7lb/in2)(144in2)F = lbInward force on windowF = P x AF = (5.4 lb/in2)(144in2)F= 777.6lb
28 Net Force on window Net Force = Force out – Force in 3/25/2017Net Force on windowNet Force = Force out – Force inNet Force = lb – lbNet Force = lbThe window was originally pushing outward with a net force of 1152 lb.Therefore it needs to hold more pounds of pressure ( – 1152)
29 3/25/2017PressurePressure acts equally in all direction at any point in a fluid and therefore it is a scalar
30 Absolute vs. Gage Pressure 3/25/2017Absolute vs. Gage PressureWhen we fill a tire to 30lb/in2 is that the absolute or the gage pressure?Atmospheric pressure = 14.7 lb/in2
31 Absolute Pressure Gage Pressure 3/25/2017Absolute PressureTotal pressure compared to a perfect vacuumGage PressurePressure measured above atmospheric pressureG.P = Total pressure – atmospheric pressure
32 Gage pressure is generally measured “with a gage” 3/25/2017Gage pressure is generally measured “with a gage”Total Pressure
33 Pressure Tire gage reads 38lb/in2 What is the atmospheric pressure? 3/25/2017PressureTire gage reads 38lb/in2What is the atmospheric pressure?What is the gage pressure?What is the total pressure?
34 Pressure What is the atmospheric pressure? What is the gage pressure? 3/25/2017PressureTire gage reads 38lb/in2What is the atmospheric pressure?What is the gage pressure?What is the total pressure?14.7 lb/in238 lb/in238 lb/in lb/in2 =52.7 lb/in2
35 How does pressure change with depth? 3/25/2017How does pressure change with depth?Where is the pressure greater the shallow end or the deep end?Why?
36 Pressure increases with depth 3/25/2017Pressure increases with depthThere is more water sitting on top of the deep endThere is twice as much weightTwice as much forceTwice as much pressure
37 Relationship between pressure and depth 3/25/2017Relationship between pressure and depth
38 Water Pressure Calculation 3/25/2017Water Pressure CalculationGiven:The height of the water in a storage tank is 100 ft above the valve. The weight density of water is 62.4 lb/ft3Find:The pressure at the valve in lb/ft2
39 Water Pressure Calculation 3/25/2017Water Pressure CalculationP = pw x hP = (62.4 lb/ft3)(100ft)P = 6240 lb/ft2Given: 1 ft2 = 144 in2Now find:Pressure in PSI
40 Water Pressure Calculation 3/25/2017Water Pressure CalculationP = pw x hP = (62.4 lb/ft3)(100ft)P = 6240 lb/ft2Given: 1 ft2 = 144 in2p = (6240 lb/ft2)(1ft2/144in2)P = 43.3 lb/in2 (psi)
41 Balanced pressure across the valve 3/25/2017Balanced pressure across the valve
42 Unbalanced pressure across the valve 3/25/2017Unbalanced pressure across the valve
43 Pressure on bottom does not depend on the size of the tank 3/25/2017Pressure on bottom does not depend on the size of the tank
44 Pressure acts like forces 3/25/2017Pressure acts like forcesPressure is a prime moverMeasuring PressuresManometer – instrument used to measure fluid pressure
45 Hydraulic lift Liquids are incompressible 3/25/2017Hydraulic liftLiquids are incompressibleAir compressor increases the pressure to the fluidLarge pushing force is exerted on the lifting piston
46 Hydraulic jack? Large cylinder to a small cylinder 3/25/2017Hydraulic jack?Large cylinder to a small cylinderSame pressure = more force in the smaller cylinderSmall to large = allowable force but small increments?
47 3/25/2017An enclosed fluid under pressure exerts that pressure throughout its volume and against any surface containing it. That's called 'Pascal's Principle', and allows a hydraulic lift to generate large amounts of FORCE from the application of a small FORCE. Assume a small piston (one square inch area) applies a weight of 1 lbs. to a confined hydraulic fluid. That provides a pressure of 1 lbs. per square inch throughout the fluid. If another larger piston with an area of 10 square inches is in contact with the fluid, that piston will feel a force of 1 lbs/square inch x 10 square inches = 10 lbs.
48 3/25/2017So we can apply 1 lbs. to the small piston and get 10 lbs. of force to lift a heavy object with the large piston. Is this 'getting something for nothing'? Unfortunately, no. Just as a lever provides more force near the fulcrum in exchange for more distance further away, the hydraulic lift merely converts work (force x distance) at the smaller piston for the SAME work at the larger one. In the example, when the smaller piston moves a distance of 10 inches it displaces 10 cubic inch of fluid. That 10 cubic inch displaced at the 10 square inch piston moves it only 1 inch, so a small force and larger distance has been exchanged for a large force through a smaller distance.
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