Pressure
Buoyancy
Archimedes Principle
Fluid Mechanics
Potpourri
100
This is the mathematical formula for pressure.
What is F/A?
100
Things float in water when their density is less than this.
What is the density of water, or
what is 1.0 g/cm3 or
what is 1000 kg/m3?
100
Archimedes lived about this date in time.
What is 287 - 212 BC?
Any date between 300 and 200 BC is good.
100
This principle describes how airplanes fly.
What is Bernoulli's principle?
100
P (pressure) is defined to be ______/______?
What is a Force / Area?
(N/m2 is OK)
200
This is pressure measured at a depth in a liquid NOT including atmospheric pressure.
What is gauge pressure?
200
This is the density of water (in kg/m3).
This is the density of water (in g/cm3)
What is 1000?
What is 1?
200
The king of Syracuse, in Sicily, commissioned him to do something that really concerned the king.
What was, "he thought that his crown was not pure gold, but that the goldsmith had mixed in some silver with the gold and kept some of the pure old for himself."
200
Bernoulli's principle says that the faster that a fluid flows, the lower the __________________. (All else being equal.)
What is pressure?
200
What pressure is felt by a body 10.m below the surface of a lake?
P = ρgh = (103kg)(9.8 m/s2)(10m) = 98000 Pa
(98000 N/m2 is OK, and I will also accept about 100000 N/m2 or 100000 Pa)
300
This is the SI unit of pressure.
What is pascals (Pa)? (N/m2)
300
This is the buoyant force on an object that displaces a volume of 1 m3.
What is 9800 N? (1000kg is NOT acceptable - that's mass)
The density of water is 1000kg/m3 --> 9800 N
Fg = mg = (1000 kg)(9.8 m/s2) = 9800 N
The mass displaced is 1000kg since the density of water = 1000 kg/m3. But the weight is 9.8 times that.
300
This is what Archimedes was doing when he realized how to determine the volume of the irregularly shaped crown.
What is bathing in a public bath?
(Running naked in the street yelling "eureka" is acceptable... actually +100)
300
Fluids are not this. (Gases are...)
What is compressible?
300
A1v1 = A2v2 This formula is called what?
What is the continuity principle?
400
A coffee table has a mass of 12 kg and sits on 4 legs, each with an area of 15cm2. This is the pressure exerted on the floor by EACH leg. (Answer in N/cm2)
What is about 2 N/cm2? Better: 19600 N/m2
(3kg)(9.8 m/s2) = 29.4 N
15 cm2 = 0.0015 m2 -->
P = (29.4N)/(0.0015 m2) = 19600 Pa
400
Apparent weight is equal to weight minus this.
What is buoyant force (FB)
400
This happened in a public bath that caused him to realize how he could determine the volume of the king's crown.
What is water overflowed? He realized that the volume of the water that overflowed was the same as the volume of his own body.
400
Pascal's principle says that F1/A1 = this.
What is F2/A2?
400
A car weighing 9000 N is on a hydraulic lift. The size of the pad on which it sits is 40 m2 while the surface area of the place where the force is applied is 0.4 m2.
What force is need to lift this car, applying Pascal's principle?
F2/A2 = F1/A1
F2 = (9000N)(0.4/40) = 90N
500
This is the ABSOLUTE pressure experienced by a diver who is 10m below the surface of the ocean. (You can approximate g=10m/s2, answer in kPa)
What is 100 kPa?
pgh = (1000)(10)(10) = 100000 Pa = 100 kPa
(98 kPa is more accurate)
500
This is the apparent weight of a 10kg object, in water, with a volume of .002 m3.
What is 78.4N? ...80N is OK.
The weight is decreased by the weight of the water displaced:
Fg = (10 kg)(9.8 m/s2) = 98 N
(0.002 m3)(1000 kg/m3) = 2 kg --> 19.6N
2 kg weighs: FB = (2 kg)(9.8 m/s2) = 19.6N
98N - 19.6N = 78.4 N ... 80N is close enough for credit.
500
This is an invention of Archimedes' that allowed one to pump water out of a boat/ship.
What is Archimedes' screw?
500
This is a system in which force is applied to a piston in a small liquid reservoir, leading to a larger liquid reservoir and a larger piston upon which a greater force is then applied, though moving an object a much smaller distance.
Using such a device you lift a 1500N device by applying only 15N of force. If the area you applied a force was 20 cm2, what was the area under the device moved?
What is a hydraulic press?
Also, what is (20 cm2)(1500N/15N) = 2000 cm2
+100 for converting to m2 = 0.2 m2
500
A square pinewood raft is 4.0 m on a side and weighs 2000 N. How far down will it sink into the water?
What is 0.034m or 3.4 cm
ρwater = 103 kg/m3
FB = weight of displaced water, & since it floats = weight of raft (2000N).
FB = 2000N = (16.0m2)(103 kg/m3)(9.8m/s2)h
2000Nm = 58,800N(h)
h = 0.034m = 3.4 cm = 1 1/3 inch