11Other Densities Platinum Diamond Chromium Tin (white) Tin (gray) 21.45 3/25/2017PlatinumDiamondChromiumTin (white)Tin (gray)21.457.157.2655.769
12What 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
13What 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
14Density 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
15Specific 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
193/25/2017HydrometerInstrument that measures density or specific gravity of fluidsCan you drown in quick sand?
20Force per unit area exerted by a fluid 3/25/2017PressureForce per unit area exerted by a fluid
21Force 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
22What 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?
23Force 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
24Outward 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
25Net 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.
263/25/2017Net 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
27Outward 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
28Net 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)
293/25/2017PressurePressure acts equally in all direction at any point in a fluid and therefore it is a scalar
30Absolute 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
31Absolute Pressure Gage Pressure 3/25/2017Absolute PressureTotal pressure compared to a perfect vacuumGage PressurePressure measured above atmospheric pressureG.P = Total pressure – atmospheric pressure
32Gage pressure is generally measured “with a gage” 3/25/2017Gage pressure is generally measured “with a gage”Total Pressure
33Pressure 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?
34Pressure 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
35How 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?
36Pressure 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
37Relationship between pressure and depth 3/25/2017Relationship between pressure and depth
38Water 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
39Water 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
41Balanced pressure across the valve 3/25/2017Balanced pressure across the valve
42Unbalanced pressure across the valve 3/25/2017Unbalanced pressure across the valve
43Pressure 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
44Pressure acts like forces 3/25/2017Pressure acts like forcesPressure is a prime moverMeasuring PressuresManometer – instrument used to measure fluid pressure
45Hydraulic 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
46Hydraulic 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?
473/25/2017An 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.
483/25/2017So 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.