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Old 29th April 2008, 23:34   #1
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Default Weighing machine Puzzled me !!!

Guys, here is the situation I was weighing my suit cases with a weighing machine (The normal type, you stand up on that and see the weight on the dial). I kept the suit case on the machine and the corners were touching the ground, it was giving incorrect results.So I stood up on the machine and lifted the suitcase, and my weight was subtracted from the total weight to get the weight of the suit case.
Now the question is, when I lift the suit case just above the ground level, its showing a different weight and if I keep the suitcase on my head its showing a different weight!
Is this really possible? My understanding is that since me and suit case is acting as a single body it should show the same weight always. Is it the weighing machine showing incorrect results?
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Old 30th April 2008, 00:30   #2
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Quote:
Originally Posted by Superleggera View Post
Guys, here is the situation

Is this really possible? My understanding is that since me and suit case is acting as a single body it should show the same weight always. Is it the weighing machine showing incorrect results?

my first thought is if you just lift it above ground level, the weight shift of the platform causes a corner to touch the body too early without passing it on to the transducer.

let me guess, when you keep it on your head, it shows a higher weight. That is the correct weight!

another explanation is if you are not dead still, the weight will keep fluctuating and may be u saw a transient value. Ruled out if you kept noticing the reading for a couple of seconds.
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Old 30th April 2008, 00:33   #3
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Weighing machines are know to show correct weight when you stand straight. If your body is leaning forward or backward, the machine can show inaccurate results.

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Old 30th April 2008, 00:36   #4
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I've noticed this too,though the difference was always minimal.
Holding the suitcases on your head gives you better stability,and the weight is fairly accurate. Hold the boxes in your hands,and you'll tend to lean to a side,hence changing the weight.
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Old 30th April 2008, 04:23   #5
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An apt question coming from a guy named superleggera

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Originally Posted by Superleggera View Post
My understanding is that – since me and suit case is acting as a single body – it should show the same weight always.
You are correct here.
The combined weight never changes regardless of whether you hold the bag out in front of you, on your head or with a fishing pole. (Though the fishing pole's weight will be added as well).

What makes the reading change is the quality of the weighing scale, which can show different values when you move the weight around. Some weighing scales even show you a different weight if you put more weight on your right foot than your left! This is what is probably causing your problem.

cya
R

Last edited by Rehaan : 30th April 2008 at 04:24.
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Old 30th April 2008, 23:05   #6
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Problem is more of COG (Center of Gravity) than of the weight scale.

Theoretically, the COG of the weight and of the load cell/load springs must lie vertically in a straight line. This reason why the docs ask the cadets to stand straight and note the readings for defence physicals ;-)
Practically, the loadcell types of scales have least error but are expensive. The spring tension dial types are popular and more prone.

When you just lift the suitcase off the ground the COG of the combined body moves vertically off why the error in reading. Lifting the case overhead is the most accurate way of getting a fair figure but DO watch your back!

Cheers

Last edited by Rehaan : 1st May 2008 at 08:10. Reason: typos corrected.
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