Calculating Kinetic Energy...

[Bruce]

...........Why hasn't there been a ban on posting homework questions?

 

[Chris Haynes]

...........Why hasn't there been a ban on posting homework questions?

Because we may not give the right answer!

 

[epepke]

Re: Re: Re: Re: Calculating Kinetic Energy...

I know that kg is sup[posed to be mass, but the way everybody screws around with the systems, it ends up being listed as weight, which is not mass, and I get sorely confused as to which I am given.

Stylus force on turntables is usually given in grams. That's just wrong.

 

[rwguinn]

Re: Re: Re: Re: Re: Calculating Kinetic Energy...

Stylus force on turntables is usually given in grams. That's just wrong.

so is selling "reality enhancer" by the Kilogram...
see the problem?

 

[epepke]

Re: Re: Re: Re: Re: Re: Calculating Kinetic Energy...

so is selling "reality enhancer" by the Kilogram...
see the problem?

Of course I see the problem. (Besides, stylus force is also called stylus pressure, which is also just wrong.) I'm agreeing with you. Earth to rwguinn, is anybody out there?

 

[Ziggurat]

Ok, so where do you live and do all your work?

When I say g isn't a constant, I really mean that, in every sense of the word. It is measurably different in different locations, even on the surface of the earth. It is affected by altitude, it is affected by lattitude, it is affected by the phase of the moon (hence tides), it is even effected by the kind of rock you're sitting on top of, and again, all these differences are measurable. So g is not a constant, but ANY definition.

 

[Ziggurat]

how stupid do you have to be to understand that when somebody says "all have the same unit" he is not equating the values--just the unit.

I'm afraid you're mistaken. You are confusing units with dimensions. Joules are a unit. An electron-volt is a unit. These units are NOT the same. They are both units of energy. Energy, however, is not a unit. It is a dimension. So you can say that electron-volts and joules have the same dimensions, but again, they are NOT the same units. Kilograms and pounds, however, do not have the same dimensions (one is mass, the other is force, aka weight).

It's always best not to get pendantic AND insulting in the same post: it can bite you on the backside if you mess up.

 

[rwguinn]

I'm afraid you're mistaken. You are confusing units with dimensions. Joules are a unit. An electron-volt is a unit. These units are NOT the same. They are both units of energy. Energy, however, is not a unit. It is a dimension. So you can say that electron-volts and joules have the same dimensions, but again, they are NOT the same units. Kilograms and pounds, however, do not have the same dimensions (one is mass, the other is force, aka weight).

It's always best not to get pendantic AND insulting in the same post: it can bite you on the backside if you mess up.

Engineers (Practical science practitioners) generally refer to them as units. One does dimensional analysis on the units of measure.
being pedantic on terminology and putting up false trails whilst avoiding the issue is a sign of the Id-10-T syndrome...

 

[Ziggurat]

Engineers (Practical science practitioners) generally refer to them as units.

"Them" being what? Energy, or Joules? Joules are a unit. Energy is a dimension. Units and dimensions are not the same thing. I'm not sure exactly what you're trying to say, but I really couldn't care if engineers confuse the two all the time, they're still different.

One does dimensional analysis on the units of measure.

Yes. Because units have intrinsic dimensions. But dimensions do not have intrinsic units, and there are multiple common units to describe many dimensions.

 

[rwguinn]

"Them" being what? Energy, or Joules? Joules are a unit. Energy is a dimension. Units and dimensions are not the same thing. I'm not sure exactly what you're trying to say, but I really couldn't care if engineers confuse the two all the time, they're still different.



Yes. Because units have intrinsic dimensions. But dimensions do not have intrinsic units, and there are multiple common units to describe many dimensions.

Units of measure:
Joule
meter
foot
pound force
pound mass
Newton
Gauss
dyne
horsepower
inch
gram
kilogram
volt
ampere
etc, etc
pressure has the units of force divided by area, or simply to support the yurpeen perversity, Pascal
and so on.
why bother?

 

[Ziggurat]

Units of measure:
...
and so on.
why bother?

Let's go back to what started this argument, your statement:
"It never obvious that a kg-m is a "Joule", nor that a Newton/m^2 should be a "Pascal", (what wrong with N/m^2 ?) or that an ElectronVolt, Calorie and Newton-meter should all have the same unit ("Joule")"

Smike was correct to point out that this statement is wrong. An electron-volt, a calorie, and a newton do not have the same units. After all, they ARE units. What they do have in common is their dimension, but dimesion is not the same as unit. One could argue that while not strictly correct, your statement could be understood easily enough in terms of dimensions instead of units. But that's not the position you took. You called Smike an idiot, said that he was wrong, and claimed that your original statement was correct. But Smike was right, your original statement is not correct.

 

[rwguinn]

Let's go back to what started this argument, your statement:
"It never obvious that a kg-m is a "Joule", nor that a Newton/m^2 should be a "Pascal", (what wrong with N/m^2 ?) or that an ElectronVolt, Calorie and Newton-meter should all have the same unit ("Joule")"

Smike was correct to point out that this statement is wrong. An electron-volt, a calorie, and a newton do not have the same units. After all, they ARE units. What they do have in common is their dimension, but dimesion is not the same as unit. One could argue that while not strictly correct, your statement could be understood easily enough in terms of dimensions instead of units. But that's not the position you took. You called Smike an idiot, said that he was wrong, and claimed that your original statement was correct. But Smike was right, your original statement is not correct.

Ok, all you folks.
Stay off the airplanes, automobiles, busses--and for the sake of your lives, stay off of and out of any constructed artifact.
Ziggurat the infallible has decreed that certainly everything I have done is totally incorrect and liable to break.
Most of the contributers here are not skeptics--they are cynics and sematicistswho simply live to be right.That's all, folks

Roger W Guinn, Licensed Engineer
F-35 JSF, MCI G4500, D4500L, Clementine, Tethered Satellite, SCATHA, TITAN 34D, F-16, F111
Analysis and loads.

 

[Ziggurat]

Ok, all you folks.
Stay off the airplanes, automobiles, busses--and for the sake of your lives, stay off of and out of any constructed artifact.
Ziggurat the infallible has decreed that certainly everything I have done is totally incorrect and liable to break.

I have little doubt that the engineering you do is probably quite good. I also have little doubt that you actually understand units and dimensions. None of that, however, will change the fact that what you wrote was, strictly speaking, incorrect. When someone pointed out that you were wrong on a semantic detail, rather than conceding the point but focusing on what your main point originally was (which was how the relationship of different units in the metric system isn't actually totally obvious), you called Smike an idiot. So I defended Smike, because he was correct. I really don't know why you attacked Smike rather than arguing what was originally your main point, and what Smike never actually refuted.

Roger W Guinn, Licensed Engineer
F-35 JSF, MCI G4500, D4500L, Clementine, Tethered Satellite, SCATHA, TITAN 34D, F-16, F111
Analysis and loads.

How nice. Argument from authority doesn't work here.