Atmospheric pressure and weight measurement

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Discussion Overview

The discussion revolves around the significance of atmospheric pressure being referred to as 100 kPa and its implications for weight measurement, particularly in relation to digital weighing scales. Participants explore the relationship between atmospheric pressure, the weight of air, and how scales measure weight.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants question the meaning of 100 kPa and whether it equates to 10,000 kg/m² acting upon us.
  • One participant asserts that 100 kPa is what is measured, implying it is a standard reference for atmospheric pressure.
  • Another participant calculates that the force required to lift a column of mercury measuring 76 cm is 101,000 N, suggesting a discrepancy in understanding the relationship between pressure and weight.
  • Concerns are raised about why a digital weighing scale does not register the combined force of body weight and atmospheric pressure, with suggestions that scales may only reflect body weight.
  • A response clarifies that the pressure acts on all parts of the scale, indicating that the net pressure forces are zero, which may explain the readings observed.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of atmospheric pressure and its effects on weight measurement. No consensus is reached regarding the implications of atmospheric pressure on digital scales.

Contextual Notes

Participants discuss the assumptions underlying the measurements of atmospheric pressure and the mechanics of weighing scales, but these assumptions remain unresolved.

Who May Find This Useful

This discussion may be of interest to those studying physics, engineering, or anyone curious about the principles of pressure and weight measurement in practical applications.

cyriac
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Whats the significance of Atmospheric pressure being refereed as 100kPa ? Does that really mean 10000 kg/m2 acting upon us ?

If we are measuring only collision force on the surface and not the weight of the entire column of air above us, then why figure 100kPa (100000 N force/m2) which is huge and significantly more than what is required to raise mercury level by just 76 cm
 
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"Why 100kPa?" That is what is measured.
 
cyriac said:
why figure 100kPa (100000 N force/m2) which is huge and significantly more than what is required to raise mercury level by just 76 cm
The density of mercury is 13.54 g/(cm^3), so a square meter of mercury with 76 cm thickness weighs 10300 kg, and would need a force of 101000N to lift it up.
 
Hi
Thanks for replying
Then why a digital weighing scale doesn't pick that force. When we stand shouldn't it pick up 80kg + 10000kg ?
Or is the scale being adjusted only to reflect body weight
 
cyriac said:
Hi
Thanks for replying
Then why a digital weighing scale doesn't pick that force. When we stand shouldn't it pick up 80kg + 10000kg ?
Or is the scale being adjusted only to reflect body weight
The scale doesn't have to be "adjusted." The pressure acts on all parts of the scale, including parts facing downward (which receive an upward force from below). The net pressure forces on the scale are zero.
 
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