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  • File : 1318369942.png-(16 KB, 552x648, Untitled.png)
    16 KB FAGGATRON_3000 !!PEF7BVl3fW0 10/11/11(Tue)17:52 No.3886863  
    90% of first year students get this wrong, can you solve it?
    >> Anonymous 10/11/11(Tue)17:54 No.3886872
    Different pressures.
    >> Anonymous 10/11/11(Tue)17:57 No.3886887
    >>3886872
    are you a troll?

    its the same pressure.
    >> Anonymous 10/11/11(Tue)18:00 No.3886900
    Same pressure that the centre. Different pressures at the sides.
    >> Anonymous 10/11/11(Tue)18:00 No.3886902
    >>3886887
    There's 1/100,000th the water on the right than the left.

    There's more pressure on the right right.
    >> Krakengineer !!5XY+x7grkpt 10/11/11(Tue)18:01 No.3886905
    >>3886887
    The force of water pressure on an object is proportional to the fluid column above it, the mass of the fluid column to the right is less. They are not the same.
    >> Anonymous 10/11/11(Tue)18:03 No.3886910
    They have the same pressure even at the sides.
    >> Anonymous 10/11/11(Tue)18:06 No.3886924
    >>3886905
    >>3886902
    no1: the formula it P = g*rho*h
    and look! g, rho and h are the same in both!

    no2:
    pressure is force per area,
    force is mass * g, thus it is proportional to the area,
    take the force and divide it by the area, now the area dependence is gone!
    >> Anonymous 10/11/11(Tue)18:07 No.3886928
    >>3886902
    >>3886905
    Swim 10' down in a small but deep pool, like one of those practice diving pools.
    Swim 10' down in the ocean.

    Same pressure, or different?
    Answer: not exactly the same cause seawater weighs a bit more than pure water, but pretty darned close.
    >> Krakengineer !!5XY+x7grkpt 10/11/11(Tue)18:12 No.3886948
    >>3886924 force is mass * g, thus it is proportional to the area

    The mass of the column to the right is less. The area at the bottoms are the same in both cases. There is less pressure.

    >>3886928
    What makes this situation different is that the diameter of the column of water on the right expands at the bottom. The unit water pressure is distributed over a larger area. If we were dealing with two cylinders the water pressure would be equal regardless of the diameter.
    >> Anonymous 10/11/11(Tue)18:12 No.3886949
    depends
    >> Anonymous 10/11/11(Tue)18:15 No.3886962
         File1318371353.png-(923 B, 168x41, 51c1e96f5b03dceb3635b9e62170d5(...).png)
    923 B
    >>3886948
    Here is a hint for you.
    >> Anonymous 10/11/11(Tue)18:17 No.3886969
    Hydrostatic Paradoxon in da house, bitches.
    >> Anonymous 10/11/11(Tue)18:18 No.3886973
    >>3886948
    >The mass of the column to the right is less. The area at the bottoms are the same in both cases. There is less pressure.
    where are you getting this? have you studied engineering or are you only impersonating one? the tube width does not make a difference. only the height of the water.
    >> Anonymous 10/11/11(Tue)18:20 No.3886984
         File1318371653.png-(59 KB, 320x282, Boyle'sSelfFlowingFlask.png)
    59 KB
    >>3886948
    so you think this would work?
    >> Teacup !obkpuSWh5M 10/11/11(Tue)18:21 No.3886992
    Obviously the one on the right has more pressure because there's more water.

    A fucking housewife could get this right you ape.
    >> Anonymous 10/11/11(Tue)18:22 No.3886993
    saw this the other day and put it on the board in the break room of the astronomy group, as much as it is uncomfortable to say, the pressure is the same.
    >> Teacup !obkpuSWh5M 10/11/11(Tue)18:22 No.3886997
    >>3886992
    *left
    >> Krakengineer !!5XY+x7grkpt 10/11/11(Tue)18:24 No.3887006
    >>3886962

    P = F / A
    The question does not give the area at the bottoms of the tanks, let's assume it's 1m^2.

    Case 1
    F =Mass*Acceleration = 1000 Kg * 9.8m/s/s = 9800 N
    P = F / A = 9800 n / 1m^2 = 9800 Pa


    Case 2
    F = Mass * Acceleration = 0.01 kg * 9.8m/s/s = 0.01 * 9.8 = 0.098 n
    P = F / A = 0.098 n / 1m^2 = 0.098 Pa


    9800 Pa does not equal 0.098 Pa. What seams to be the problem?
    >> Anonymous 10/11/11(Tue)18:25 No.3887015
    If we replaced the upper columns of water with movable, watertight weights equal to the mass of the water, we would not have the same pressure.

    Therefore, the pressures in the two cylinders are different.
    >> Anonymous 10/11/11(Tue)18:28 No.3887025
         File1318372083.png-(5 KB, 581x421, sss.png)
    5 KB
    sup?
    >> Anonymous 10/11/11(Tue)18:29 No.3887030
    >>3887006
    first case:
    F = 1000 Kg * 9.8m/s/s = 9800 N
    P = F / A = 9800 n / 1m^2 = 9800 Pa

    second:
    F = Mass * Acceleration = 0.01 kg * 9.8m/s/s = 0.01 * 9.8 = 0.098 N
    P at diameter change: F / A = 0.098 N/0.00001m = 9800Pa
    force on water in 1m^3 tube: 9800Pa*1m^3 = 9800Pa

    9800Pa = 9800Pa

    you fucking moron.
    >> Anonymous 10/11/11(Tue)18:30 No.3887032
    >>3887025
    Aw shit nigga,
    >> Anonymous 10/11/11(Tue)18:31 No.3887035
    >>3887006
    >2 different objects
    >same area?

    Idk if troll or just stupid.
    Tripfag at his finest..
    >> Krakengineer !!5XY+x7grkpt 10/11/11(Tue)18:33 No.3887047
    >>3887030 P at diameter change: F / A = 0.098 N/0.00001m = 9800Pa

    >> 0.00001m
    The diagram shows that the area where the rocks are stationed are the same diameter.
    >> Anonymous 10/11/11(Tue)18:35 No.3887052
    >>3887047
    thats why i used
    >force on water in 1m^3 tube: 9800Pa*1m^3 = 9800Pa
    >1m^3
    read the whole thing, that's the force btw, you need to divide it by 1m^3 again, (hint this gives 9800Pa)
    >> Anonymous 10/11/11(Tue)18:35 No.3887053
    >>3887015
    wrong. We would have the same pressure. You're stupid and a nigger.
    >> Anonymous 10/11/11(Tue)18:36 No.3887056
    p = rho * g * h
    >> Anonymous 10/11/11(Tue)18:37 No.3887057
    >>3886984
    Until friction and turbulence eliminate the flow, yes, in some sense it works.
    >> Anonymous 10/11/11(Tue)18:37 No.3887061
         File1318372664.png-(8 KB, 581x421, 1318372083593.png)
    8 KB
    if the presure is not the same, this would happen,
    >> Anonymous 10/11/11(Tue)18:38 No.3887062
         File1318372688.png-(24 KB, 1245x421, 1318372083593.png)
    24 KB
    >>3887025

    DUN DUN DUN
    >> Anonymous 10/11/11(Tue)18:38 No.3887065
    >>3887061
    This is exactly right. Anyone who still thinks it'd be the same is an idiot.
    >> Anonymous 10/11/11(Tue)18:39 No.3887066
    >>3887061
    actually, I should be nicer. This is 4chan, after all.
    Anyone who still thinks the pressures are different should pay better attention.
    >> Anonymous 10/11/11(Tue)18:41 No.3887074
    >>3887061
    Amazing. While all the VIOLENT SIMIANS here are squabbling over equations and imaginary science, this prime specimen proposes that you can solve this problem with experimentation instead.

    Now that, my primate friends- is real science. Take notes you lowly apes.
    >> Krakengineer !!5XY+x7grkpt 10/11/11(Tue)18:41 No.3887075
    >>3887061
    You are confusing pressure with force.
    >> Anonymous 10/11/11(Tue)18:42 No.3887081
    >>3887062
    No. Disk on the right needs a smaller surface area for it to be analogous.
    >> Anonymous 10/11/11(Tue)18:44 No.3887085
    >>3887062
    wrong, its not equivalent to the question

    first consider the top part of both containers (the skinny bit on the right one and the same part on the fat one), pressure scales only with depth so at the bottom of both of these parts have the same pressure.

    at the transition from the skinny part to the fat part the pressure at the boundary match so the top of the fat bit of the one on the right has the same pressure as the same bit on the left one. below this again pressure scales with depth, hence the pressure is the same.
    >> Anonymous 10/11/11(Tue)18:44 No.3887087
         File1318373078.jpg-(38 KB, 400x400, 1307576907917.jpg)
    38 KB
    >gather 10000 straws
    >put them together to make a long chain
    >fill with water
    >put it on objects
    >break everything with shit loads of pressure>problem science?
    >> Anonymous 10/11/11(Tue)18:44 No.3887088
         File1318373078.png-(7 KB, 581x421, 1318372083593.png)
    7 KB
    the this will happen!
    >> Anonymous 10/11/11(Tue)18:45 No.3887090
    >>3887065
    Congrats, you've created a perpetuum mobile.
    >> Anonymous 10/11/11(Tue)18:46 No.3887091
         File1318373185.gif-(354 KB, 300x300, 1304060612231.gif)
    354 KB
    >swimming in the ocean
    >dive 1 feet
    >suddenly the pressure of the whole ocean is on you
    >explode
    >> Anonymous 10/11/11(Tue)18:46 No.3887092
         File1318373194.png-(9 KB, 581x421, 1318373078513.png)
    9 KB
    >>3887088
    add a turbine and free energy!
    >> Anonymous 10/11/11(Tue)18:46 No.3887093
    forgetting that its 1 ml - not 1m (10^-3)^2 which would be dividing by 1 millionth therefore it is equal.
    >> Anonymous 10/11/11(Tue)18:48 No.3887097
    >>3887088
    thank you for simply explaining that boyle's self filling flask does not work.

    You should put that mind to more productive use, like figuring out to make a bong out of a klein bottle.
    >> Krakengineer !!5XY+x7grkpt 10/11/11(Tue)18:49 No.3887103
         File1318373392.gif-(85 KB, 480x600, 10-son-i-am-disappoint.gif)
    85 KB
    >>3887085 pressure scales only with depth

    That is only when the area of the water column remains equal to the area the force is effecting, which is not the case here. MFW 95% of /sci/ falls for troll physics.
    >> Anonymous 10/11/11(Tue)18:54 No.3887121
    >>3887103
    im gonna assume you are a troll, no one can be this retarded.
    >That is only when the area of the water column remains equal to the area the force is effecting,
    no, see>>3887030
    >> Anonymous 10/11/11(Tue)18:54 No.3887122
    the /g/ thread is much more productive.
    >> Anonymous 10/11/11(Tue)18:54 No.3887123
    >>3887103
    i described that for the top part and the bottom part of the right hand container the pressure scales with depth. at the boundary between the top and bottom parts the pressure must match. so the bottom part starts with the same pressure ans the bottom of the skinny part, so yes pressure scales with depth, the extra pressure comes from the top of the fat part of the container around the end of the skinny part.

    try again this isn't troll physics.
    >> Anonymous 10/11/11(Tue)18:54 No.3887124
    P = gamma(h)

    H is the same. Gamma is the same. The pressure is therefore the same.
    >> Anonymous 10/11/11(Tue)18:55 No.3887128
    >>3887030
    this is only within the tubes. at the bottom the areas are equal.
    >> Anonymous 10/11/11(Tue)18:57 No.3887134
    >>3887128
    thats why I used the area of 1m^3 in both calculations.
    >> Anonymous 10/11/11(Tue)19:00 No.3887143
         File1318374054.png-(22 KB, 779x421, 1318372083593.png)
    22 KB
    BRB PATENT OFFICE
    >> Anonymous 10/11/11(Tue)19:01 No.3887145
    >>3887103
    Krakengineer, what do you think the pressure is just above the widening of the cylinder? How about just below it?
    >> Anonymous 10/11/11(Tue)19:02 No.3887156
    >>3887134
    if you're >>3887006
    then yes, you're right. but i was refering to >>3887030 who did it wrong.

    for the record. rho g h only applies if you say V=h*A which is not the case here. the bottom cross section is the A and if you do A*h you get the volume of a cylinder the size of the one on the left when in reality its much less. pressure = weight/area. the area of the bottoms is the same, the right one has left weight. figure it out
    >> Anonymous 10/11/11(Tue)19:04 No.3887163
    I know hardly any physics at all. Here is my attempt: There is a larger mass of water in the left tank compared to the right, meaning a larger force will be exerted on the same surface area (Mass*Acceleration of Gravity). Since the surface area is the same, the pressure on the object and the bottom of the tank on the left is larger than the pressure on the object and bottom of the tank on the right. Where did I go wrong?
    >> Anonymous 10/11/11(Tue)19:06 No.3887179
    >>3887156
    i am >>3887030
    and i did it correctly, i used the smaller diameter up to the point where it became wider, then used the wider diameter of 1m^3, and get the and pressure.
    >>3887006
    is wrong
    >> Anonymous 10/11/11(Tue)19:08 No.3887194
    >>3887103

    Incorrect. Pressure only scales with depth. Look it up. Consider the force from the weight of the water in both situations. The first one is gamma(A)(h) where A is the cross sectional area of the tube and h is the height. The Force induces a pressure at the interface whose magnitude is F/A or gamma(h). The same analysis can be done on the other tube, but notice how the area cancels. Therefore Pressure scales only with depth. P = gamma(h). You're wrong. Take it from an engineer.

    >>3887163

    That's wrong because the surface area is not the same.

    >>3887179

    The force on the object is the same, but you certainly did not prove it correctly. 9800PA * 1 m^3 = 9800 Pa? Seriously? Your method was wrong, your units are wrong, and your proof is wrong.
    >> Anonymous 10/11/11(Tue)19:10 No.3887201
    >>3887194
    I figured that the equal and opposite force to the weight of the water must be applied along the bottom of the tank. Both tanks have equal surface area bottoms. Where did I go wrong this time?
    >> Anonymous 10/11/11(Tue)19:11 No.3887203
    >>3887194
    >>3887194
    ya, that last Pa should be N. congratulations! you are the first person to spot it so it seems the first person who even read it all the way through. have a doughnut.
    >> Rainbow Dash !!Q/yRC4LcWxp 10/11/11(Tue)19:11 No.3887205
    >>3887061
    That is what happens, though exaggerated.

    Two words:
    Capillary action
    >> Anonymous 10/11/11(Tue)19:13 No.3887215
    >>3887179

    no you did it wrong.
    force on water at transition is .098 newtons, you said it was the pressure. you wanted to say it was the force and then calculate the pressure with P=F/A with the new A at the bottom. what you did was calculate the pressure in the tube, say that that was the pressure in the bottom, and then reverse engineer the same answer as the left side.
    >> Anonymous 10/11/11(Tue)19:13 No.3887217
    Pressure is force per unit area, faggots.

    P = F/A
    F = volume * Density
    V = A * Height
    P = A*H*D/A

    P = H*D

    FUCKING HINT IF YOU'RE RETARDED:

    THE PRESSURE DOES NOT DEPEND ON
    HORIZONTAL AREA OF THE STRAW OF THE WATER.

    SAME PRESSURES.
    >> Anonymous 10/11/11(Tue)19:14 No.3887223
    >>3887194
    [x] Hydrotold!
    >> Anonymous 10/11/11(Tue)19:15 No.3887224
    >>3887215
    too bad, >>3887203
    already got the doughnut.
    >> Anonymous 10/11/11(Tue)19:17 No.3887235
    >>3887194
    you are wrong sir. so much for your engineering skills
    rho g h comes from P=F/A, F=ma. m=rhoV and V=hA.

    this is true sometimes but in OPs example V≠hA because A is the A of the bottom and if you take h* that A you get a volume equal to the tube on the left, not the right.

    instead you should use P=F/A or pressure = weight divided by area. the area is the bottom where the rock is, so they're equal, and obviously the left has more weight.
    >> Anonymous 10/11/11(Tue)19:17 No.3887237
    >>3887179
    >>3887194
    >>3887217
    please keep fighting the good fight i need sleep.
    >> Anonymous 10/11/11(Tue)19:18 No.3887238
    People who think the pressure is less in the setup on the right: what do you think is going on at the interface of the two tubes?

    Just above the interface, the pressure is the same in either case. There can be no finite jump in pressure across the interface. Consider a very thin cylindrical control volume straddling the interface (axis parallel to the symmetry axis). Its mass can be made arbitrarily small, the only way it can be in equilibrium is if the pressure is continuous across the interface: the pressure in the wide part is the same in both cases. The pressure at the bottom is the same in both cases.
    >> Rainbow Dash !!Q/yRC4LcWxp 10/11/11(Tue)19:19 No.3887245
    To whomever thinks the pressures are the same.

    If you step into a bathtub and I put a really long straw into it, do you really think I could crush you with 1 cup of water?

    Actually think this through, just because you know the equations doesn't mean you have to throw basic reasoning out the window.
    >> Anonymous 10/11/11(Tue)19:20 No.3887250
    >>3887239
    yes, it will crush you, assuming the bath is sealed airtight.
    >> Anonymous 10/11/11(Tue)19:20 No.3887252
    >>3887245
    yes it will.
    >> Anonymous 10/11/11(Tue)19:20 No.3887253
    >>3887239
    If the bathtub is sealed and the straw is 10m high, then yes. you can crush me with just water. It is possible, because each of the walls of the tub would need to push against the straw per unit area.

    Pressures are the same:

    P = D * g * H
    pressure, density, gravity, height.
    >> Anonymous 10/11/11(Tue)19:20 No.3887254
    These ones always trick people. Same goes for tension problems.
    >> Anonymous 10/11/11(Tue)19:21 No.3887256
    >>3887217
    see
    >>3887235
    V≠hA


    >>3887224

    i wasnt comparing your units im saying your method was wrong. you wanted to use the force and instead you used the pressure. you didnt mistype it, you actually did it wrong.

    >>3887006
    did it right
    >> Rainbow Dash !!Q/yRC4LcWxp 10/11/11(Tue)19:21 No.3887260
    >>3887250
    >>3887250
    No it won't.

    You are an ignorant little human who doesn't understand anything. Put a transparent straw in a cup of water, the water will actually flow up the straw above the water level.

    LEARN 2 CAPILLARY ACTION
    >> Anonymous 10/11/11(Tue)19:23 No.3887271
    >>3887201
    Someone answer me.
    >> Anonymous 10/11/11(Tue)19:24 No.3887274
    >>3887253
    >>3887252
    >>3887250

    NO

    thats not how science works. positioning of 1lb of water does not change the fact that it is 1lb of water.

    please god read
    >>3887235
    >>3887256
    and stop saying rho g h


    YOU CANNOT USE RHO G H HERE AS THE AREA AT THE BOTTOM IS DIFFERENT THAN THE AREA AT THE TOP, THIS V≠hA

    OK?
    >> Krakengineer !!5XY+x7grkpt 10/11/11(Tue)19:24 No.3887276
    >>3887145
    At the point just before the cylinder on the right widens the pressures are equal.
    P1 = F1 / A1 = 9800 n / 1m^2 = 9800 Pa
    P2 = F2 / A2 = 0.098 N/0.00001m^2 = 9800Pa

    After the tube on the right widens the area increases but the force of gravity from the water above remains the same, so the pressure drops.
    P2 = F2 / A2 = 0.098 n / 1m^2 = 0.098 Pa

    I can't believe all of /sci/ is being trolled because they don't realize their pressure depth formulas don't account for situations like this. The force of gravity on the two water columns is not equal, but the area the force acts on AT THE BOTTOM is equal, so the pressure is not equal.

    Saying the pressure is the same in both cases is like saying 100 men will be pushed down on by a shared load of 10kg as much as by a shared load of 10000kg.
    >> Anonymous 10/11/11(Tue)19:24 No.3887278
    >>3887260
    >>3887256
    ok you know what, fine, keep on being ignorant. im done, i dont care anymore, two more idiots among millions isn't going to make a difference. il be in a interesting thread if you need me.
    >> Anonymous 10/11/11(Tue)19:25 No.3887280
    >>3887271
    you had it right in the beginning, the other guy was wrong. the right one has less pressure.
    >> Rainbow Dash !!Q/yRC4LcWxp 10/11/11(Tue)19:26 No.3887291
    >>3887278
    You simply don't understand how the implementation of RhoGH works.
    >> Anonymous 10/11/11(Tue)19:26 No.3887293
    >>3887276

    Then please refer to this post:
    >>3887238
    There can't be a sudden drop in pressure as the tube widens in a steady state configuration.



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