Linear Scale

[Guest jezebel]

Hello, I put a box on a scale to see how heavy it was. The scale only went up to ten kilos but the box was heavier than that. However, the needle did spin around 1.5 times so I figured the box was about 15kgs. Then someone came out with the comment, "You're no scientist, are you! It's not a linear scale. Once it goes past that point it is no longer accurate." Is that true.

 

TIA,

 

Jez

[Ophiolite]

It depends upon how accurate you want to be. Your friend is correct that the response of the scale (probably determined by overcoming resistance to a spring) is not linear. In fact it is not linear over any portion of its weighing range - but how accurate do you want to be? I am assuming these are ordinary office scales for parcels - 10 kilos sounds a lot for kitchen scales. Within the designated range it will be pretty accurate: I would imagine an object that weighs in at 8kg would be within 100g either way of that weight. As you go beyond the upper limit you will become increasingly inaccurate. However, you covered that inaccuracy by noting 'about' 15 kgs. To me 'about' 15 kgs, means somewhere between 14 and 16 kgs. I think there is a good chance you still have that level of accuracy, but not much more than that.

[swansont]

No need to post the same question in multiple places.

[Asimov Pupil]

so how does it work is it one of those inversely proportional to distance formulas for the EP of the spring as you compact it more?

[mezarashi]

What he means is just that any device engineered by us has a range of operation. Beyond this range, you cannot expect any precise or accurate results. What was the scale on your scale? The cause of the inproportionality may be due to many things depending on the design of the scale, so I wouldn't know.