If you're too heavy for one scale...

[Bogie]

...will two of them and a plank between them work to average the weight?

I _really_ would like to check the tongue-weight on my trailer - I'm supposed to have it under 500, but I don't know where to get an inexpensive scale that goes that high... Durn van looks like it's squattin' pretty heavy.

Bet y'all thunk there was a different reason?

[LisaS]

physics not my strongest suit - but it should work - when you are rehab-ing an injury you often stand on two scales to make sure only XX% of your weight is on the recovering leg -
you could always test it with yourself on the plank :)

[Gaelen]

or see if the local UHaul or Taylor Rental (anywhere that rents out trailers) has a truck scale you could drive it over...

[Bogie]

Yeah, but they charge every time. I know I'm not putting 2,500 in the trailer, but I want to make sure I'm not exceeding 500 pounds tongue weight.

[cmcole]

Are there any roadside scales that weigh transport trucks?
Perhaps they could let you ride over them for free?

[Bogie]

That generally works fine for axle weight.

Trailer 101: When you're loading a trailer, it is better to have the weight forward, to prevent it swaying as you drive down the road. This can be a bad thing when being passed by big rigs. However, if you put too much too far forward, you pass the recommended tongue weight for your hitch/vehicle.

[Nean]

:)Oh, is that what those wiggly, waggly trailer towin' folks are doing wrong! (we need a head smakin' smiley!)
I al's learn somethin' from you - just never know what it's gonna be.:D

[deirdra]

Can you weigh each thing you are putting in it? When I moved, my employer would pay for anything up to 3000 lbs, so I weighed my boxes (mostly books & other heavy things) and my 2995 sum was right on the mark. The movers had estimated 1500 based on volume.

Can you test your 2-scale theory by weighing yourself on 2 scales? I believe scales measure Force, in which case two scales may weigh most of you twice (part of the force would be on the other scale, but not necessarily half, which is why it would be good to test something whose weight you know). The plank idea would work if scales measured Stress (force per unit area) but I don't that is what scales measure (if they did, you'd weigh less in shoes, which have more area than feet). If something weighs 500 lbs, it may damage the springs or other mechanisms in a 300 lb max scale.

[hawk]

Got my curiousity up?? What weighs 2500 pounds in a trailer in the first place??

[mcsblues]

Can you weigh each thing you are putting in it? When I moved, my employer would pay for anything up to 3000 lbs, so I weighed my boxes (mostly books & other heavy things) and my 2995 sum was right on the mark. The movers had estimated 1500 based on volume.

Can you test your 2-scale theory by weighing yourself on 2 scales? I believe scales measure Force, in which case two scales may weigh most of you twice (part of the force would be on the other scale, but not necessarily half, which is why it would be good to test something whose weight you know). The plank idea would work if scales measured Stress (force per unit area) but I don't that is what scales measure (if they did, you'd weigh less in shoes, which have more area than feet). If something weighs 500 lbs, it may damage the springs or other mechanisms in a 300 lb max scale.

Scales measure force - either by levers acting on a calibrated spring (mechanical scale) or by levers deflecting a metal beam and that deflection being measured (electronic scale). Either way there is no possibility of you measuring this force (gravity x your mass) twice. You can shift your weight from one foot to another, from no weight resting on one scale to the other extreme and everything in between - in all cases the sum of the two readings will be the same. The same principle is in action on a single scale if you move your weight off centre the levers on that side will apply more force to the spring and the levers on the other side, less.

[Bogie]

Mostly it's a lot of camping crap, some t-shirt stuff, generators, etc., etc....

[hawk]

Do you just use it for storage? Nosey me..
I have a 5X7 full also.

[Bogie]

Oh, no... It goes camping, goes to the range. Benchrest shooters tend to have a lot of luggage.

And I think I've been, outside of matches, twice this year... Maybe next...

[deirdra]

You can shift your weight from one foot to another, from no weight resting on one scale to the other extreme and everything in between - in all cases the sum of the two readings will be the same.This may be true in theory, but not in practise due to the way bathroom scales are designed for humans with two feet. I weighed myself and then stood with my weight equally distributed with one foot on the scale and one foot on a book at the same height. The recorded weight was never half of my weight, it was always higher and highly variable, depending on where I stood. One reading for "half" my weight was 100 lbs - 47% higher than it really is. This same scale gives very repeatable readings to the nearest 0.2 lbs if I stand on it with both feet in the same spots like you are supposed to. The scale seems to get confused if you try to measure half humans and since trailers don't have feet, they would probably confuse it more.:rolleyes:

[mcsblues]

Eh? :lol: How do you know exactly half your weight is on the book? If your 'two feet' theory is right, do you weigh something different if you stand on one foot (with the other in the air) compared to both feet on the scale?

I know I shouldn't laugh, but you would be overturning some pretty fundamental laws of physics if you really couldn't weigh objects in as many fractions as you like.

[deirdra]

With a Ph.D. in Geophysics, I know quite a bit about the laws of physics and also how difficult it is to apply them to nature or any non-theoretical problem because the accuracy of the measurement tool is critical (and led to a 500-year controversy concerning the weight of Earth);) . Your first assumption, that bathroom scales measure weight perfectly, no matter where the weight is positioned, is what is questionable, and why I suggested a trial run with two scales & a known weight. I don't know that I perfectly divided my weight between the book and the scale, which is why I tried it a dozen times, and found it curious that none of the readings were less than half my weight, they were all more than half my weight (yes, I know that >30 tries are needed for a statistically valid sample). If I had used a different brand of scale, I probably would have gotten a different answer. The design of a digital scale requires you to stand in the same spots to get the same weight and it is designed to be accurate over a particular range. Just try measuring something that weighs a kilo on your bathroom scale and a kitchen scale to see that 100% errors are possible; I used this argument to get my vet to buy a baby scale to weigh cats, when I noticed that my cat's weight varied by 50% on the big dog scale (kitty was sitting still in a carrier, not wiggling around on the industrial scale). I suspect the same is true at the high end of the scale's range since Young's Modulus for metal varies with temperature and applied stress in a non-linear fashion. I hope no anorexics buy a scale like mine, since it apparently "reads high" :eek: in the 68-lb range and they would think they need to lose more.

[mcsblues]

Of course any inaccuracies of your scale(s) need to be taken into account , and if you use multiple scales the errors will be multiplied, but as I recall, your original objection to this method was that parts of your body could be measured twice ... which is very definately contary to physics, and could not happen regardless of the scale design. As for your sample size, when none of the tests eliminates the human factor (I'm sure you could put less than half your weight on the scale if you wanted/tried to, just as you obviously can put more) it wouldn't make any difference to the validity of the experiment to add more 'samples'.

[deirdra]

There are 2 endmembers of weighing with 2 scales. Put the scales at infinity and the center of gravity in between and the object will weigh 0 (the force vector is not in line with either scale). Put one scale on top of the other and the total weight will be 2X the weight of the object plus the weight of the upper scale. With 2 scales side by side and the center of gravity wavering above both (and the digital scale measuring non-instantaneous strain, not force directly, according to your description), it would be very difficult to get an accurate instantaneous force measurement with a couple of bathroom scales. This is what I meant by weighing twice - not that you actually weigh twice as much, but that you cannot take two readings instantaneously so the sum of the two scale readings could be as high as 2X the actual weight (or more if the weight is swaying and there is an additional acceleration term).

What Bogie really needs is a large fish/mammal weighing scale, with the spring above, not below, the weight. It is the only way to know that the center of gravity is aligned with the spring along the force vector. The scale would also have to be corrected for elevation relative to the geoid and Bogie would have to make sure there are no nearby mountains or ore bodies or he will end up weighing part of them too. As someone else mentioned, no wonder you see so many wobbly trailers on the road. Accurately weighing and distributing the contents is not easy!

[mcsblues]

We probably should let this go :lol: but the "force vector" you are measuring here is gravity - and as we all remember from elementary science, your weight or the weight of Bogie's trailer is your/its mass times the acceleration of gravity. Now ignoring minor anomalies, on Earth for the purposes of this exercise the 'force vector' is straight 'down' (ie perpendicular to a scale or scales on a level surface) and at sea level on this planet (well certainly this side of the equator) by definition mass and weight will be identical. It doesn't make the slightest difference where the COG is in relation to the scales, and measuring this force from above or below will also have no impact on the result. Imagine what would happen if you had two fish scales with the weight supported somewhere along a beam connecting the two - again this would be an effective way to use two scales to weigh something outside of the capacity of one. Balance beam scales work in a similar fashion by shifting the pivot point and using a smaller weight proportional to its distance from the pivot.)

So! - if you or the trailer are not jumping around - this force can be measured by one scale (by the combined action of the force applied to the four levers) or multiple scales with in the accuracy limits of the scales themselves. If you put an infinite distance between the scales with the the COG resting anywhere in between , you would doubtless end up with a nonsense result (just as you would with fish scales) ... because at least one of the scales would be be measuring the effects of gravity in some other galaxy! ... but in the real world, the suggestion that Bogie uses two scales with a tared plank between them is practical and should be reasonably accurate (the scales' accuracy being the only limiting factor).

[Bogie]

Sheesh, guys, I'm weighing camping stuff, not gunpowder...

FWIW, I've got two nice balances, and a $100 piece of crap electronic dealie that I use for that...

I've also got a mg scale that I bought sight-unseen from a guy, and it turned out to be one of those electronic analog abominations... I hate it because I can't get it to keep anything even remotely resembling a zero (including closed container, solid rest).

I'll just go buy a scale or two, analog, thank you very much, and see what they say... Since I know what I weigh, I may be able to test them in the store (at least close enough for horseshoes, hand grenades, and small tactical nuclear weapons...).