Social Social Thread - Talk About Anything (You Are Allowed to Talk About)!

[The Star King]

ballin, going into the hundreds for height doesn't matter AT ALL. It might seem bad to you because you're not used to it, but it's totally natural for other people, and it's easier to convert/standardized.

 

[cheeseball341]

Congrats america.

Time to show those hippy *****ez whats up.

Spoiler

 

[dandan]

decimal system is so much easier than duodecimal system.
you can also use decimeter if you want to (means 10 centimeters).

is ricky really 197, damn.
i am 188 and the highest smasher i knew off till now was smakis from sweden who is like 195.

 

[SuPeRbOoM]

high five 5'10 people

 

[ciaza]

use collapse tags for large images homo

like this:

Spoiler

yes, that was just an excuse to post my picture =3

 

[Olikus]

Im a good example why meter looks better. 179 cm. Whats that? 5'10 3/4 or something?

And dandan your not even the tallest in the euro chat. Both maddy and stan/ddiz are atleast 190.

 

[asianaussie]

me and boom are the same height

except im asian so i automatically get a 20cm handicap

 

[Surri-Sama]

I R 5'7

prob shortest player xP

 

[dandan]

Im a good example why meter looks better. 179 cm. Whats that? 5'10 3/4 or something?

And dandan your not even the tallest in the euro chat. Both maddy and stan/ddiz are atleast 190.

read the post again please :D

 

[Sempiternity]

Haha I'm actually grading my college's intro fluids class, they just went over this. This is a pretty general equation, applying it really depends on the situation but I'll do my best.

Basically sum of forces on the fluids is equal to the two integrals on the RHS. For steady state flow (which you should be dealing with no?) the first term is 0 because it includes a d/dt and in steady state, flow doesn't vary with time. For the most part you won't worry about this.

Now look at the second term. It is an intergral over a differential Area, which sounds tough but it ends up just being the values at the exit minus the values at the entrance (bear with me). For example, Vxyz2*rho2*Vxyz2 (dotted) A2 - Vxyz1*rho1*Vxyz1 (dotted) A1 . Now if you're dealing with incompressible flow density is constant, so rho2 = rho1 = rho. Vxyz2 and Vxyz1 are simply velocity vectors at the exit and entrance, respectively. A2 and A1 are vectors normal to the exit and inlet areas (I think in the outward direction? Whatever convention your class is using). Then you just pound out the dot product of Vxyz and A for entrance and exit, do the scalar multiplication and subtraction to find the sum of the forces.

I hope that helps, no guarantee I'll be on to answer more questions tonight sorry man.

Thanks! I actually have somewhat of a grasp on the equation, but thanks for the clarification on what cancels to zero and a more in depth explanation of the second integral. The hardest part of this class for me is recognizing the different types of problems, figuring out what assumptions I can make, and then knowing what certain assumptions do to the equation at hand. Now I know how steady and incompressible flow affect problems.

Any other tips you can give me in the meantime for dealing with different problem types? We've covered up to Bernoulli's Equation so far and I have an exam tomorrow. Just looking for tricks of the trade since our professor is pretty bad at teaching and the book is convoluted as all hell. I'm mainly looking for key words or situations to look for that allow me to make assumptions, which in turn let me get rid of terms in my giant equations.

Also, the second integral in the above equation is sometimes written as a summation in the solution manuals. Why is this? In what situations can you use a summation and not an integral? Or are they both basically the same thing?

 

[Peek~]

I R 5'7

prob shortest player xP

Im right in between 5'5-5'6

Feels bad man

 

[Surri-Sama]

Lol i never really cared to much about height...being a person who enjoyed playing sports in my youngest years, i definitely would have rather been tall / have more mass then i did. But i GREW out of that pretty quick.

Someone on Kaillera once told me i have a napoleon complex as well, which is odd because this is the first time I've ever mentioned my actual size :o ...except to marth...and it might have been him trolling me so who knows

 

[clubbadubba]

[COLLAPSE="Quoted"]

Thanks! I actually have somewhat of a grasp on the equation, but thanks for the clarification on what cancels to zero and a more in depth explanation of the second integral. The hardest part of this class for me is recognizing the different types of problems, figuring out what assumptions I can make, and then knowing what certain assumptions do to the equation at hand. Now I know how steady and incompressible flow affect problems.

Any other tips you can give me in the meantime for dealing with different problem types? We've covered up to Bernoulli's Equation so far and I have an exam tomorrow. Just looking for tricks of the trade since our professor is pretty bad at teaching and the book is convoluted as all hell. I'm mainly looking for key words or situations to look for that allow me to make assumptions, which in turn let me get rid of terms in my giant equations.

Also, the second integral in the above equation is sometimes written as a summation in the solution manuals. Why is this? In what situations can you use a summation and not an integral? Or are they both basically the same thing?

[/COLLAPSE]

You sound like you are on the right track. It's basically what you said, you have to make the right assumptions. At this point in your class, I highly doubt any flow you do would be anything other than incompressible and steady. Not really much I can tell you without a specific problem in mind, but make sure you know the assumptions required to use each equation (like Bernouli's, incomp, inviscid, steady? I think).

As far as the summation goes, an integral is just an infinite summation, so they could be the same thing. I haven't seen what this summation looks like though, maybe it is summing all the entrance and exit points from the control system which is what the integral does. Good luck on your test tomorrow!

Also as an engineer, English units are miserable. I used to be all about them, but they are just non-sensical. Nothing is on a decimal scale of 10. The scale for Fahrenheit is arbitray whereas Celsius is based on water. Pound force and pound mass don't convert directly, it's a mess.

 

[Sempiternity]

Spoiler

you sound like you are on the right track. It's basically what you said, you have to make the right assumptions. At this point in your class, i highly doubt any flow you do would be anything other than incompressible and steady. Not really much i can tell you without a specific problem in mind, but make sure you know the assumptions required to use each equation (like bernouli's, incomp, inviscid, steady? I think).

As far as the summation goes, an integral is just an infinite summation, so they could be the same thing. I haven't seen what this summation looks like though, maybe it is summing all the entrance and exit points from the control system which is what the integral does. Good luck on your test tomorrow!

Also as an engineer, english units are miserable. I used to be all about them, but they are just non-sensical. Nothing is on a decimal scale of 10. The scale for fahrenheit is arbitray whereas celsius is based on water. Pound force and pound mass don't convert directly, it's a mess.

What exactly does uniform flow mean? Does that mean the flow is inviscid and I can ignore surface forces? i.e. water flowing through a tube would have no shear stresses and would look like this:

Spoiler

_____
     |
     |
     |
-------

as opposed to:

_____
      \
       |
       /
-------

How can I apply the assumption of uniform (inviscid?) flow to that gnarly equation or all equations in general?

The body force is zero when there is no force due to gravity, i.e. working in a horizontal plane, yes?



Also, any chance you could sneak a peak at this Bernoulli problem?

http://www.engr.uconn.edu/~wchiu/ME3250FluidDynamicsI/solutions/Problem 6.42.pdf

I'm confused as to what they're doing with the velocities at point 2 in both parts. It seems like the first it goes to zero because its... stagnant? I really have no idea. Why is v2 in part b not zero?

Sorry for the bombardment of questions, haha, but this should all be fairly straightforward... Again, thanks so much for your time!

 

[ballin4life]

I dont think anyone disagrees that celsius is better than farenheit.

eh. farenheit gives a nice breakdown where 60s is cool, 70s is nice, 80s is warm, and 90s is hot. I don't see much advantage to celsius, but not much disadvantage either.

ballin, going into the hundreds for height doesn't matter AT ALL. It might seem bad to you because you're not used to it, but it's totally natural for other people, and it's easier to convert/standardized.

duh? of course it's totally natural to people who have used that system for their whole lives. That doesn't change the fact that the units are inconveniently sized.

decimal system is so much easier than duodecimal system.
you can also use decimeter if you want to (means 10 centimeters).

haha i know what a decimeter is. but no one ever uses those.

Also as an engineer, English units are miserable. I used to be all about them, but they are just non-sensical. Nothing is on a decimal scale of 10. The scale for Fahrenheit is arbitray whereas Celsius is based on water. Pound force and pound mass don't convert directly, it's a mess.

you know that 10 is an arbitrary number right? also celsius temperature makes no sense compared to kelvin. there's also no particular reason pound force and pound mass should convert, considering that they are different things, but a pound force is just a pound mass * standard gravity.

Anyway for science it really doesn't matter what system you use. My only point is that meters are an inconvenient length.

 

[The Star King]

duh? of course it's totally natural to people who have used that system for their whole lives. That doesn't change the fact that the units are inconvenient.

you know that 10 is an arbitrary number right?

Anyway for science it really doesn't matter what system you use. My only point is that meters are an inconvenient length.

OK, then WHY is it inconvenient? All you've said so far is that you have to use hundreds.

Uh, powers of 10 are the easiest number to multiply and divide by. Derp? Unless you're arguing for society using something other than base 10 >___>

 

[ballin4life]

OK, then WHY is it inconvenient? All you've said so far is that you have to use hundreds.

Yes. In order to describe something accurately you have to break out more digits, because meters are too big and centimeters are too small.

Uh, powers of 10 are the easiest number to multiply and divide by. Derp? Unless you're arguing for society using something other than base 10 >___>

multiples of 3 are going to have more divisors and thus will be easier to split up (i.e. will give integer values).

Maybe it's time to start the crusade for metric time. 10 hours a day, 100 minutes in an hour, 100 seconds in a minute right?

 

[dandan]

10 base is the easiest for people to grasp as our rudimentary math uses 10 base.

about getting into the hundreds, what about long distances?
in the metric system you just use kilometer as 1000 meters and the conversion is easy and simple, whereas you use miles, which are 5280 feet or 1760 yards.
no matter how you look at it, it does not make as much sense (unless i am overlooking something, and if that is the case, enlighten me).

 

[ballin4life]

Why does anyone need to know how many feet are in a mile anyway?

The mile is a pretty messed up one though haha.

Like I said my only gripe is that meters are too big for many day to day uses unless you go into decimals.

 

[Sangoku]

Meters are too big? What does that mean?

 

[Olikus]

eh. farenheit gives a nice breakdown where 60s is cool, 70s is nice, 80s is warm, and 90s is hot. I don't see much advantage to celsius, but not much disadvantage either.

With celcius. water freeze at 0 and boils at 100. it makes sence

 

[Sempiternity]

As an engineer (almost), the metric system blows the US customary way out of the water. The whole pound*force pound*mass thing is silly, and what's even more silly is that we use weight while the metric system uses mass in day-to-day measurements. I'm not entirely sure who's in the wrong, but with mass, there is zero confusion. We should really start measuring things in slugs. I "weigh" 4.35 slugs!

But the fact that the metric system is base 10 practically makes the world go round. It is so easy to go from unit to unit and change order of magnitudes. Whenever I get a problem in English units, I die a little inside, and if I'm really struggling, I'll just convert everything to metric and bang out the problem that way.

kip!? What the **** is a kip?! It's all about Nm, baby.

Oh yeah, and Celsius (I never know if that words looks right) is much better for doing calculations (converted to Kelvin) than Fahrenheit (not too sure about that one, either). Although, I do like the broader range of values, which makes describing weather easier. Rankine? Do people even use that?!

 

[clubbadubba]

All I know is that I've never met a scientist or engineer or actually prefers English units. English units of height are more complex than metric because you actually use 2 different units (ft, inches), not to mention it can take as many digits to describe height in English system as in metric (5'10" = 3 inches). I do agree that we should just use kelvin or rankine as the temperature scale, and neither one is superior to the other there. The English system of force and mass sucks though. It wouldn't be bad if only lbf and slugs were used, but too often lbm is used, which requires a constant to satisfy the 2nd law. It's just an extra element of complexity with no redeeming qualities. And then an ounce is 1/16 of a lb, and lower than that anyone know? The metric system allows you to use prefixes to get whatever range you want, and always stays within the 10 base system. If English had like a 12 base system, it would be better as long as it were consistent, but it can't even do that. I can't think of a way English > metric, and the only reason the US doesn't convert is that the infrastructure is already in place and would cost $ to change.

What exactly does uniform flow mean? Does that mean the flow is inviscid and I can ignore surface forces? i.e. water flowing through a tube would have no shear stresses and would look like this:

Yes exactly.

How can I apply the assumption of uniform (inviscid?) flow to that gnarly equation or all equations in general?

Well you know that you can use one velocity to represent the flow across an entire area since there is only one velocity over the area.

The body force is zero when there is no force due to gravity, i.e. working in a horizontal plane, yes?

Ummm not quite sure what you mean by body force. Force due to gravity is certainly 0 in a horizontal plane though.

I'm confused as to what they're doing with the velocities at point 2 in both parts. It seems like the first it goes to zero because its... stagnant? I really have no idea. Why is v2 in part b not zero?

Yes the first goes to zero because it is stagnant, exactly. The second velocity is not stagnant though. Imagine shooting the jet to the right to a vertical wall, and at the wall the jet splits into up and down components along the wall. The first pressure tap is located right at the point where the jet splits, or where it hits the wall and becomes stagnant. The 2nd tap is located some distance up or down from the split location, so it has velocity.

 

[Sempiternity]

Well you know that you can use one velocity to represent the flow across an entire area since there is only one velocity over the area.

So is it safe to assume that most of the problems I'll be doing will be uniform in flow?

Ummm not quite sure what you mean by body force. Force due to gravity is certainly 0 in a horizontal plane though.

By body force, I mean F_b in the momentum equation we discussed earlier. As far as I know, it's basically mg, or rho*g*Volume, but zero in a horizontal plane.

Yes the first goes to zero because it is stagnant, exactly. The second velocity is not stagnant though. Imagine shooting the jet to the right to a vertical wall, and at the wall the jet splits into up and down components along the wall. The first pressure tap is located right at the point where the jet splits, or where it hits the wall and becomes stagnant. The 2nd tap is located some distance up or down from the split location, so it has velocity.

Thanks, that clears it up. The solutions hardly explain what they're doing...

Also, what exactly does this mean?

Spoiler

It looks like the second integral of the momentum equation, but that random rho is throwing me off.

 

[Battlecow]

Swear to god, we have the metric v imperial argument every other week.

They both work fine. Imperial's more AMERICAN, but Celsius is a little bit easier on OCD people, so eh, both about equal.

 

[clubbadubba]

Most likely uniform flow yea, unless it specifically says otherwise I would think.

Hmmm I think by body force it means forces exerted on the particles such as gravity and electromagnetism (the latter of which will not come up at all). Just know that the momentum equation you showed had already canceled out the "body force."

That equation is basically saying that what goes in must come out, i.e. mass flow is constant. Mass flow is equal to rho*V*A, or in integral from int(rho*V*dA), and that integral equals 0 going from an entrance to an exit. However you know incompressible flow means rho is constant right? Therefore in incompressible flow, rho is constant and can be pulled out of the integral, and since the whole thing equals 0 it just goes away. In compressible flow, rho is not constant but rather is a function of the cross-sectional area you are talking about, so you can't pull it out of the integral. So the incompressible version is just a simplified version of the compressible version with the assumption that rho is constant.

Also, that is not the second integral of momentum, it is mass conservation. They are two different conservation laws, and I'm actually grading HW's as I type where you have to use both in conjunction lol.

 

[Sempiternity]

Alright, thanks. I keep getting the different laws confused. They all look the same... I think I understand this a little better now, though.

 

[clubbadubba]

Rankine? Do people even use that?!

Anyone in the US who makes engines is using Rankine almost exclusively. Rankine and Kelvin are both absolute temperature scales with arbitrary degrees, so neither is really better.

 

[The Star King]

Yes. In order to describe something accurately you have to break out more digits, because meters are too big and centimeters are too small.



multiples of 3 are going to have more divisors and thus will be easier to split up (i.e. will give integer values).

Maybe it's time to start the crusade for metric time. 10 hours a day, 100 minutes in an hour, 100 seconds in a minute right?

...SO? You're getting on my nerves. You have to use hundreds. So? Is that too big for your brain to handle? You didn't seem to have a problem saying that you bench sub 135. Or was that so very INCONVENIENT for you?

Lolno. So what if you get more integers? 10 is easier to multiply and divide by in your head. I don't see how you can even argue against this.

The day is based off of one rotation of the Earth, so you can't divide it evenly with multiples of 10. NVM I'M DUM IGNORE THIS

How did you even get in the Debate Hall?

 

[asianaussie]

The same way everyone else did: by sticking to their guns no matter what, formatting posts appropriately and generally telling everyone else they're wrong, even when they're agreeing with you.

So Americans hate metric because three digits is way too much for them to handle?

 

[The Star King]

Apparently that's ballin's reasoning, even though you need three digits to describe your weight in imperial units as well as many other things, such as weightlifting, as ballin so kindly demonstrated for us in the previous freaking page. Incredible.

 

[asianaussie]

Can you hurry up and take over the US so you can formally convert the primary system to metric?

 

[The Star King]

ok brb taking over US

Oh, I just realized you COULD divide a day by 10s easily, and I'm not sure why I said otherwise. DERP. You would only be unable to change the number of days per year. That was pretty stupid of me. I can admit when I'm wrong.

 

[clubbadubba]

ok brb taking over US

Oh, I just realized you COULD divide a day by 10s by just changing how long a second is. DERP. You would only be unable to change the number of days per year. That was pretty stupid of me. I can admit when I'm wrong.

lol was gonna say this, but you caught yourself, good job.

But like I said the US has so much infrastructure related to the English system that it would be inefficient to change it. So rather than everyone in the US be sad that they are using an inferior measuring system they can't change, they just bash metric and live in denial. I used to be like that and honestly if I didn't work with numbers all the time I would still be like that.

 

[The Star King]

Yeah it would be extremely hard to change. Even as I joke that I'll start a revolution I'm not sure if we should do it. But pretending the imperial system isn't worse is silly.

 

[Sempiternity]

Anyone in the US who makes engines is using Rankine almost exclusively. Rankine and Kelvin are both absolute temperature scales with arbitrary degrees, so neither is really better.

Yeah, I realized that after... we actually used a wee bit of Rankine in thermo. Hell, the guy even has a famous cycle named after him...

 

[ballin4life]

...SO? You're getting on my nerves. You have to use hundreds. So? Is that too big for your brain to handle? You didn't seem to have a problem saying that you bench sub 135. Or was that so very INCONVENIENT for you?

You have to use hundreds for all sorts of day to day things where you don't want to get that specific.

Weight is different because 1) there is a large range of weights and 2) you usually want to be pretty specific. It IS more convenient to say "oh I bench 9 stone and weigh 12 stone", but you actually do need more precision than that because 1 stone is a large difference (we need more precision than that). It would be more convenient though for the sake of weightlifting if there were a unit of size ~5-10 pounds.

The problem with meters is that the level of precision we usually need (say, to measure the height of a door) is in between the meter and the centimeter. You probably don't need to know that my door is 265 centimeters tall exactly, but it's also not precise enough to say that it's 3 meters tall.

Lolno. So what if you get more integers? 10 is easier to multiply and divide by in your head. I don't see how you can even argue against this.

12 would be a better base for divisibility. That's all I was saying.

It's obviously easy to divide and multiply by 10 in your head in base 10. I don't think this is that great of a benefit though for day to day use. Does anyone really care about how many feet are in a mile? I could refer to things as being in "milli-inches" or "kilo-feet" etc, and it would make sense, but ultimately miles would be more comprehensible to people that are used to thinking in miles. My ONLY POINT is that meters are of an inconvenient size for day to day use.

The day is based off of one rotation of the Earth, so you can't divide it evenly with multiples of 10. NVM I'M DUM IGNORE THIS

How did you even get in the Debate Hall?

it's great that these two statements were juxtaposed.

The same way everyone else did: by sticking to their guns no matter what, formatting posts appropriately and generally telling everyone else they're wrong, even when they're agreeing with you.

haha.

So Americans hate metric because three digits is way too much for them to handle?

So non-Americans just can't multiply and divide by numbers other than 10 huh?

 

[asianaussie]

Imperial is not an enlightened, superior or more practical system, even if you try to claim it is. Adding zeros to the end of things is far preferable to having to multiply, say, 3' 4'' by any integer.

Meters aren't impractical at all, especially when day-to-day use rarely ever goes past 'about __ metres'. Are you really going to be saying 'hey, that doorframe is 8 foot 10 inches'? I would rather say, 'a bit more than 2.5 meters' or 'about 2.6 meters'. The exception would be engineers/tradesmen, who need to be more specific, meaning that metric is better for them.

Also, I can tell you inability to perform basic integer multiplication is not the reason the world in general prefers metric. We're just picking the easier system to work with.

 

[The Star King]

You have to use hundreds for all sorts of day to day things where you don't want to get that specific.

Weight is different because 1) there is a large range of weights and 2) you usually want to be pretty specific. It IS more convenient to say "oh I bench 9 stone and weigh 12 stone", but you actually do need more precision than that because 1 stone is a large difference (we need more precision than that). It would be more convenient though for the sake of weightlifting if there were a unit of size ~5-10 pounds.

The problem with meters is that the level of precision we usually need (say, to measure the height of a door) is in between the meter and the centimeter. You probably don't need to know that my door is 265 centimeters tall exactly, but it's also not precise enough to say that it's 3 meters tall.

Sorry, but I still don't see the disadvantage the metric system has in convenience. You can use any number of figures for however specific you want to be - in your example, you can simply say your door is 2.7 meters tall. Seems neither too vague nor too precise to me. It's hard for a unit to be inconveniently sized when you can multiply and divide it by ten for a reasonable difference in size.

12 would be a better base for divisibility. That's all I was saying.

It's obviously easy to divide and multiply by 10 in your head in base 10. I don't think this is that great of a benefit though for day to day use. Does anyone really care about how many feet are in a mile? I could refer to things as being in "milli-inches" or "kilo-feet" etc, and it would make sense, but ultimately miles would be more comprehensible to people that are used to thinking in miles. My ONLY POINT is that meters are of an inconvenient size for day to day use.

So what's the value in obtaining integers when dividing?

Even if it's not very beneficial, the benefit exists. There's little reason not to use it as opposed to absurd arbitrary things such as 12 inches per foot, 5280 feet per mile, etc.

it's great that these two statements were juxtaposed.

IKR? But at least I caught myself, and I was never in the Debate Hall anyways

 

[kys]

Soooo who wants to be my partner in my ultra-cool low tier doubles tourney I'm about to host???? ANY TAKERS?

^ This is a really cool argument btw. You should all show your girlfriends to impress them.