Weight in Vacuum vs Atmosphere: A Question

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Discussion Overview

The discussion revolves around the question of whether the weight of an object differs in a vacuum compared to an atmosphere, particularly considering the effects of buoyancy provided by the atmosphere on the weight measurement.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that weight, defined as the downward force an object exerts due to gravity, is affected by the buoyant force of the surrounding medium, such as air.
  • Others argue that while buoyancy has a small effect on the measured downward force, it may not fundamentally change the definition of weight, with some proposing the term "apparent weight" for clarity.
  • A participant mentions that the buoyant force of air is approximately 1.2 kg (12 N) per m³, and provides an example involving a person with a mass of 75 kg to illustrate the minor impact of buoyancy on weight.
  • Another participant notes that for precise measurements, one should consider the density differences between the object and the material used for weighing.
  • There is a discussion about how buoyancy in air varies with altitude, as the density of air decreases with height, affecting the buoyant force experienced by an object.

Areas of Agreement / Disagreement

Participants express differing views on the implications of buoyancy on weight, with no consensus reached regarding whether buoyancy fundamentally alters the concept of weight itself.

Contextual Notes

Some assumptions regarding the definitions of weight and buoyancy may not be explicitly stated, and the discussion includes varying levels of precision regarding the effects of buoyancy in different mediums.

northern expo
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not sure if this question has been asked before, but is the weight of an object the same in a vacuum compared to weight in an atmosphere. the concerns of this question is that do we need to consider that our atmosphere provides some boyancy on our mass to change the value of weight.
 
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If by "weight" you mean the downward force that a stationary object exerts on whatever is supporting it against gravity, yes, it depends on the buoyant force of the surrounding medium. If the medium is air, we usually ignore this effect, especially in introductory textbook examples, but if you need a lot of precision you may have to take it into account. Or if the medium is dense, e.g. water.
 
Weight is the force an object feels due to gravity.
So you only feel it if you are standing on (or near) an object

Yes the boyancy of air has a small effect on the downward force.
I suppose you could split hairs and say this doesn't change the weight, it only changes the total downward force but in everyday language this is the weight - you could always say "apparent weight" if you want to be more precise
 
what is the bouyant force of air??
 
northern expo said:
what is the buoyant force of air??
About 1.2kg (12N) per m^3

If a person has a mass of 75kg and the density of water, they will have a volume of 0.075m^3 so the bouyancy of air only makes about 100g difference.
 
It gets more complicated when you want to weight something - for really precise work you should take into account density difference between object and weights material.
 
northern expo said:
what is the buoyant force of air??

Buoyancy is the force exterted upward to keep a given object afloat. In the case of air, buoyancy is proportional to altitude. As an object rises in the air its buoyancy decreases as the density of the surrounding air decreases and vice-versa as the object falls.

Hope I was able to explain that well.
 

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