Does weight scale as the cube of size?

[Chris333]

A bunch of my Nn3 rolling stock weighs next to nothing, the metal wheels probably weigh as much or more than the rest of the car. They all track just fine:

Not a valid vimeo URL

[nkalanaga]

The maximum rail weight of a 70-ton car is 220,000 pounds, so 217,000 would be about right for a loaded 70-ton boxcar.  For a loaded 50-ton car the maximum gross rail weight is 177,000 pounds, or about 19.6 grams in N scale.  Of course, having only loads in all trains is unrealistic, but the prototypes would love the revenue!

"Yes, 217,000 lbs, about 200 tons, is absurd."  It would be, but 217,000 lbs is only 108.5 tons.

[jagged ben]

Plastic has a lower density compared to every metal I can think of, except lithium.  How does that explain scaling the model up to 1:1 resulting in an unrealistically high weight(mass)?  I don't think that is the issue at all.

I thought the scaled mass is off because there is a metal base plate in the model that when scaled up is unrealistic and materially affects the mass, given it is a large proportion of the model mass to begin with.  Say the metal plate is 3 mm thick, that is 480 mm 1:1, nearly half a meter thick solid metal.

Totally agree with the second part, but with respect to the first part...

According to google, steel is about 8 times as dense as polystyrene.   The plastic walls and roof of an N-scale boxcar are probably at least 8 times as thick (adjusted for scale) as the corresponding steel parts of the prototype.   Probably 20 or 30 times.  So the plastic is probably adding quite a measure of additional mass as well, roughly 25/8 or 3 times the mass (adjusted for scale), which would actually account for most of the mass in the original post.

If both the plastic parts and the metal parts are equally over-thick, then they would account pretty equally for the over mass of the n-scale car.

[mmagliaro]

The maximum rail weight of a 70-ton car is 220,000 pounds, so 217,000 would be about right for a loaded 70-ton boxcar.  For a loaded 50-ton car the maximum gross rail weight is 177,000 pounds, or about 19.6 grams in N scale.  Of course, having only loads in all trains is unrealistic, but the prototypes would love the revenue!

"Yes, 217,000 lbs, about 200 tons, is absurd."  It would be, but 217,000 lbs is only 108.5 tons.

Whoops!  Forgot the "2".  Yes, about 108.5 tons. 

You guys are thinking more modern than I am.  I am looing at 40-foot cars with capacities of about 100,000 lbs, as printed on their
sides.  When it says "Lt Wt 45,000", that is unloaded, and the "Load Limit" is listed as 100,000 so does that mean the
car can be loaded with 50 tons of cargo, for a total weight of 145,000 lbs?

[Dave V]

I think it still comes down to the thicker sides, different material, and added weight of an N scale car as to why the weight doesn't scale by the volume.

[wazzou]

I am looing at 40-foot cars with capacities of about 100,000 lbs, as printed on their
sides.  When it says "Lt Wt 45,000", that is unloaded, and the "Load Limit" is listed as 100,000 so does that mean the
car can be loaded with 50 tons of cargo, for a total weight of 145,000 lbs?

No, 50T or 100,000 lbs is the loaded weight, so the car can be loaded with 55,000 lbs.

Edited to add....
This fact really illustrates the railroads desires to develop freight cars with larger capacities and weight limits.
Imagine how much more volume of freight is transported today versus the late 1950's, about the time the larger capacity 50', 70T cars started to gain more traction.

[up1950s]

What we need is very light cars with very heavy wheels or at least cars with the lowest cg as we can get .

[Kisatchie]

What we need is very light cars with very heavy wheels or at least cars with the lowest cg as we can get .

Hmm... I only have
flat cars with depleted
uranium wheels...

[ednadolski]

I think it still comes down to the thicker sides, different material, and added weight of an N scale car as to why the weight doesn't scale by the volume.

If you scale the gravitational constant, and the Planck length, then it all works out (allowing for inflation of course).

 

Ed

[Kisatchie]

If you scale the gravitational constant, and the Planck length, then it all works out (allowing for inflation of course).

Oh yeah. I completely forgot about the Planck length.


Hmm... and don't forget
to factor in the moon's
effect on the tides...

[unittrain]

A planck length is so small that if the period at the end of a sentence were the size of the universe a planck length would be the actual size of the period. So one atom in a freight car is like astronomically large compared to a planck length, hence  freight cars and anything else for that matter are mostly open space.

[ednadolski]

I forgot to mention, you also have to account for the additional spacetime dimensions beyond the 3 + 1.   So it scales not by the cube, but by the 10th (or is it 11th?) power.   This is because the curvature of spacetime is more significant in scales smaller than HO.

Ed

[nkalanaga]

mmagliaro:  Yes,  The "Capacity" is the nominal payload.  The "Load Limit" is the absolute maximum payload, and the "Light Weight" is just that.  The "Gross Rail Load" is the maximum weight as measured by a track scale.  The nominal capacity seldom changes, but if the LT WT is changed, for whatever reason, the LD LMT also changes. 

The CAPY is usually, but not always, standardized by truck capacity, which in turn is usually determined by journal size.  A car with "50 ton" trucks would have a nominal capacity of 110,000 lbs, or 100,000 before the early 60s, but the actual carrying capacity is determined by (GRL - LT WT).  That's why they finally, sometime in the 90s(?) quit putting the CAPY on cars.  It was basically useless.

[up1950s]

mmagliaro:  Yes,  The "Capacity" is the nominal payload.  The "Load Limit" is the absolute maximum payload, and the "Light Weight" is just that.  The "Gross Rail Load" is the maximum weight as measured by a track scale.  The nominal capacity seldom changes, but if the LT WT is changed, for whatever reason, the LD LMT also changes. 

The CAPY is usually, but not always, standardized by truck capacity, which in turn is usually determined by journal size.  A car with "50 ton" trucks would have a nominal capacity of 110,000 lbs, or 100,000 before the early 60s, but the actual carrying capacity is determined by (GRL - LT WT).  That's why they finally, sometime in the 90s(?) quit putting the CAPY on cars.  It was basically useless.

Good thing I don't model the modern age as I have a thing for capy bearers .

[peteski]

Good thing I don't model the modern age as I have a thing for capy bearers .

That is the largest hamster I've ever seen!  It will sure keep your lap warm, but it might fancy making a meal out of the train layout!