Scale vs. mass vs. weight for

[wcfn100]

I like these topic just to keep by brain sharp.  Otherwise I'd end up buying something just to figure out how it works and unfortunately it's usually expensive electronic equipment.

So anyone need anyone need any of the following:

PSP
GPS BT reciever.
Palm Pilot (x3)
IPAQ
Playstion 2
Wall light timer
Internet security camera
Infrared parking sensor
and so on....

And if you ever need to take you laptop apart, I'm your guy.


Jason

[bicknell]

So, are we now all in agreement that if you took a real railroad car, scaled it to 1:160th in all dimensions and used the exact same materials to build it the resulting mini-car would weigh (drumroll), 1/(160^3) the original car?

(For the record 160^3 is 4096000.)

[asciibaron]

So, are we now all in agreement that if you took a real railroad car, scaled it to 1:160th in all dimensions and used the exact same materials to build it the resulting mini-car would weigh (drumroll), 1/(160^3) the original car?

(For the record 160^3 is 4096000.)

no.  you forgot that it would now weigh less than a duck and therefore you are a witch and we'd have to burn you.

-Steve

[wcfn100]

So, are we now all in agreement that if you took a real railroad car, scaled it to 1:160th in all dimensions and used the exact same materials to build it the resulting mini-car would weigh (drumroll), 1/(160^3) the original car?

(For the record 160^3 is 4096000.)

Except I still contend the materials are moot as to why the equation is correct and nothing here has changed that.  A scale car represents a real car regardless of what it's made of.  The material will indeed dictate if the model car if heavier than the proto car, but thats the whole point.  You could make the car out of foam or out of rock.  They happened to be made out of plastic and thus, become heavier than the prototype.


Jason


Jason

[asciibaron]

Except I still contend the materials are moot as to why the equation is correct and nothing here has changed that.  A scale car represents a real car regardless of what it's made of.  The material will indeed dictate if the model car if heavier than the proto car, but thats the whole point.  You could make the car out of foam or out of rock.  They happened to be made out of plastic and thus, become heavier than the prototype.

it is not a scale car, it is a 3 dimensional representation of the car, only correct in the length, width, and height of specific portions - like the outside, visible areas.  the wall sheeting is easily half a scale foot wide when the prototype is 2-3 inches.  a true scaled down car would be exactly 1/160th in all dimensions, but it would still not be 1/160th of the weight.

-Steve

[wcfn100]

So I don't really model in N scale I guess.

"a true scaled down car would be exactly 1/160th in all dimensions, but it would still not be 1/160th of the weight."

Why?


Jason

[bicknell]

So, are we now all in agreement that if you took a real railroad car, scaled it to 1:160th in all dimensions and used the exact same materials to build it the resulting mini-car would weigh (drumroll), 1/(160^3) the original car?

(For the record 160^3 is 4096000.)

Except I still contend the materials are moot as to why the equation is correct and nothing here has changed that.  A scale car represents a real car regardless of what it's made of.  The material will indeed dictate if the model car if heavier than the proto car, but thats the whole point.  You could make the car out of foam or out of rock.  They happened to be made out of plastic and thus, become heavier than the prototype.

My point is that is the right baseline for if it is "heavier" or "lighter" than the prototype.  Agreed the materials and slop in scaling down are the real factors.

[Mark4]

the calculations are incorrect - mass does not scale

Why not if you had a 2 pound box in N scale, the size of that box would be 160(boxes)x160x160 in real life.

Why wouldn't the weight be 2x160x160x160?


edit: Who's talking about mass anyway, we're talking about how much something weighs.

Jason

You quote pounds - it's a unit of mass. It is defined by reference to the kilogram.

[wcfn100]

You quote pounds - it's a unit of mass. It is defined by reference to the kilogram.

Well a ton is 2000 pounds, and that's the unit railroads use when talking about weight.  I suppose I could change all of my reporting marks to newtons.

So you would say that this statement is wrong?

"In United States customary units, the pound can be either a unit of force or a unit of mass"


Jason

[Mark4]

You quote pounds - it's a unit of mass. It is defined by reference to the kilogram.

Well a ton is 2000 pounds, and that's the unit railroads use when talking about weight.  I suppose I could change all of my reporting marks to newtons.

So you would say that this statement is wrong?

"In United States customary units, the pound can be either a unit of force or a unit of mass"


Jason

No. In my experience it is used in the US as a unit of force and of mass. It raises an interesting Newtonian corollary. F=ma. Units of pounds for force, units of pounds for mass. Acceleration is dimensionless.

Back to the freightcar.   A short ton is 2000 pounds. A pound is defined as a unit of mass, ergo a ton is defined as a unit of mass. The car weighs a given number of tons ergo weight is mass in this context. From time to time the car is weighed on a weighbridge. The weighbridge is calibrated with a reference mass, traceable (ultimately) to a primary reference.

[Mark4]

We talk about N scale being 1:160th scale...  but that's one-dimensional.  An N scale boxcar occupies 1/160^3 less space... That's why an N scale layout takes up roughly one quarter the space as an HO layout (as opposed to "half the size" which is the usual lame quote).

Sloppy!
An N scale boxcar occupies 1/160^3 times the space not 1/160^3 less space.
Furthermore, the statement uses "space" as a volumetric measure then you immediately use the same word as a proxy for area.

[wcfn100]

How can a ton be a unit of mass if a ton on earth would be a 332 pounds on the moon, and mass doesn't change?

Not to mention, a ton is even defined as a unit of weight. 


Jason

[Mark4]

Isn't the weighbridge calibrated by the force of gravity on that reference mass i.e. it's weight? If there were no gravity, what would get calibrated?

And how can a ton be a unit of mass if a ton on earth would be a 332 pounds on the moon, and mass doesn't change?

Not to mention, a ton is even defined as a unit of weight.  And the term 'weighgridge' has 'weigh' in it. ???



Jason

Halve the gravitation force and you could still calibrate the weighbridge. All the bridge does is determine the ratio between the object and the reference. Don't let the measuring instrument cloud the issue.

Why do you claim that a ton would be 332 pounds on the moon? Your ton is defined as 2000 pounds. Why would it become something different? Let's say your ton is a block of steel. By taking it to the moon the volume hasn't changed nor has the density so why is it no longer 2000 pounds?

I will accept your statement that the ton is a unit of weight. I will accept that it is 2000 pounds. Assuming that we have established that the pound (by NIST's definition) is a unit of mass is it not reasonable to conclude that in this context weight is synonymous with mass?

[Chris333]

I think my DCC issue if far more important  :-*

[Mark4]

I think my DCC issue if far more important  :-*

Isn't it past your bedtime, Chris? :

It's Friday night here. I've got beer, I've got pizza, I've got a physics discussion. What a great way to start the weekend!