Does standing on bathroom scale depress or compress spring

In summary, bathroom scales work by using a spring to measure the downward force of an object's weight. This force is then translated into the corresponding weight on the scale's dial. The spring is compressed when an object is placed on the scale, and the scale measures the restoring force of the spring to determine the weight. Some scales may also use strain-gauges to measure the movement of the spring.
  • #1
Conde
8
0
I am unsure how bathroom scales work. Does your weight compress or depress the spring? Do scales measure the upward or downward force? Please explain in detail.
 
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  • #2
Conde said:
I am unsure how bathroom scales work. Does your weight compress or depress the spring? Do scales measure the upward or downward force? Please explain in detail.

Welcome to the PF.

http://en.wikipedia.org/wiki/Weighing_scale

.
 
  • #3
Thanks for your reply. I am still confused as to whether when you stand on a scale you are pushing the spring down, which sounds more likely or whether as is written in some books, the spring is pushing up. Also is your weight measured from the scale pushing up, or from your weight pushing down. I appreciate the clarification so I can really understand how the scale works.
 
  • #4
Conde said:
Thanks for your reply. I am still confused as to whether when you stand on a scale you are pushing the spring down, which sounds more likely or whether as is written in some books, the spring is pushing up. Also is your weight measured from the scale pushing up, or from your weight pushing down. I appreciate the clarification so I can really understand how the scale works.

In the linear region of the spring's action, the following equation holds:

F = -kΔx

That means that the force F down on the spring will cause its size to shrink in proportion to the force (and in relation to the "spring constant" k). So if object 2 is twice as heavy as object 1, object 2 will cause twice as big of a Δx shrinkage. The movement down of the scale platform is used to turn the indicator to the corresponding weight of the object. The farther down the spring is compressed, the more the dial moves to show the heavier weight.

More info on springs:

http://en.wikipedia.org/wiki/Spring_(device [Broken])

.
 
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  • #5
Conde said:
Thanks for your reply. I am still confused as to whether when you stand on a scale you are pushing the spring down, which sounds more likely or whether as is written in some books, the spring is pushing up. Also is your weight measured from the scale pushing up, or from your weight pushing down. I appreciate the clarification so I can really understand how the scale works.
Both! You push the spring down and in return, it pushes you back up.

All forces come in similar pairs.
 
  • #6
Plus, it could be instructive to explore the use of strain-gauges in decent scales. Springs are not the end-all.
 
  • #7
Thanks everyone,
one last question which I still do not have clarified is whether the scale is measuring the restoring force or the actual force of the weight.
 
  • #8
Conde said:
Thanks everyone,
one last question which I still do not have clarified is whether the scale is measuring the restoring force or the actual force of the weight.
It must be both or neither: because they come in pairs, it can't be one or the other. But whether it is both or neither is a choice I leave to you. To explain what the scale actually does: the scale has sensors (as turbo suggested) that directly measure the movement (strain) of the spring. The scale then calculates the force required to cause that amount of movement.
 
  • #9
You have all really clarified this for me. Thanks for your time.
 

1. Does standing on the bathroom scale affect the accuracy of the reading?

Yes, standing on the bathroom scale can affect the accuracy of the reading. When you stand on the scale, your weight compresses the spring inside the scale, causing it to stretch and give a reading. The more weight you put on the scale, the more the spring will compress, resulting in a higher reading.

2. Can the spring inside the bathroom scale become permanently compressed from standing on it?

Yes, over time, the spring inside the bathroom scale can become permanently compressed from repeated use. This can lead to inaccurate readings and the need for the scale to be replaced.

3. How does the spring inside the bathroom scale work?

The spring inside the bathroom scale is designed to compress when weight is placed on it. The amount of compression is then converted into a reading on the scale, which is displayed in units of weight, such as pounds or kilograms.

4. What happens if someone with a much heavier weight stands on the bathroom scale after someone with a lighter weight?

If someone with a much heavier weight stands on the bathroom scale after someone with a lighter weight, the spring will compress even more, resulting in a higher reading. This is because the spring has already been compressed from the first person's weight, and the additional weight will cause it to compress further.

5. Can I get an accurate reading from a bathroom scale even if I don't stand on it in the same spot every time?

No, the accuracy of the reading on a bathroom scale can be affected by standing in different spots on the scale. This is because the spring inside the scale may be more or less compressed depending on where you stand. To get the most accurate reading, it is best to stand in the same spot on the scale each time you use it.

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