spring scale question

Francis Oliver

If two 100-N weights were attached to a horizontal spring scale would the scale read 0, 100, or 200 N, or would it give some other reading?

mathmike

it would read equal

EnumaElish

IF IT HAS NEWTONS AS UNITS THEN A horizontal spring scale would read 200 N

Ordinary scales have KGs or LBs. So Newtons need to be converted to KGs or LBs.

Tide

Please explain how you arrived at 200N.

EnumaElish

The question doesn't say that the weights are placed at opposite ends. If you place 200N on the same side then that's what you'll "read": 200N.

HallsofIvy

But it does say that the spring is horizontal! Assuming this is just a simple, graduated, spring that stretches by the gravitational force on a mass, since it is horizontal there is no gravitational force and it will read 0!

EnumaElish

Do you think it's a "vertical" spring scale being held horizontally? I now realize that when I wrote my first post I replaced "horizontal" with "vertical" in my mind. Then I thought, "what's the point of holding it horizontally, maybe they meant a counter scale (see attached image)." But maybe not???

Site I downloaded the image from. Look under "Commercial" then "Counter scales."

HallsofIvy

That's a balance scale. It has no springs at all!

I really have no idea what the original problem actually said or intended. I would like to see the exact wording. The original post did specifically say "horizontal spring scale". I can only conclude that it simply isn't going to register any weight at all!

I suppose it could be a spring attached to the wall, set on a horizontal platform but with the weights to be measured hanging vertically. If that's the case, then it would measure 200 N.

Without knowing exactly what the situation is, my best guess based on the wording of the original post is that the spring is sitting on a horizontal platform as are the "weights" and so there is no extension- the spring reads 0.

EnumaElish

I guess that's right. Again I had pictured mentally that it (or some version of it) could have springs under each pan, but apparently not."I'm with you."

Francis Oliver

Hello,
Thanks a ton for all of your help. I should have been more specific though because the question is actually based off of a picture. It’s a horizontal spring scale lieing on a table with the weights attached at each end with ropes hanging off the ends of the table so that the scale is in the middle. So with that would it be 200? Really sorry about the confusion.

EnumaElish

Given this description, my answer would be 200N, or the Kg or Lb equivalent.

HallsofIvy

Aha! Yes, in that case, the spring would read 200 N. It is exactly the same as if the scale were attached to the ceiling and both weights were attached to the bottom. There would still be 200 N tension in the spring.

mukundpa

Nothing to say 'Aha'. The two weights are each of 100N and attached on each end creating tension of 100N in each string and hence the reading is 100N.
Just think you are pulling a spring from only one end. It will not get extended. To get the spring stretched we require force on either end of the spring and both are equal. These balancing forces produce elongation in the spring.
In case of vertically suspended spring one force is the weight and the other force is applied by the ceiling, which is equal and opposite. Here the two weights are providing the two forces to elongate the spring and hence the tension is 100N everywhere and the reading will be 100N.

VietDao29

mukundpa

please see the attachment
I think this was your question

Attached Files

spring balance.doc (20.5 KB, 34 views)

HallsofIvy

Yes, how foolish of me!

EnumaElish

mukundpa, I am sorry I don't "get" it: why would you read 100 and not 200N ? If two persons are tugging at a rope with 100N force each, isn't the tension 200N?