Not able to understand weight on the surface of earth

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Discussion Overview

The discussion revolves around the concept of weight as it relates to gravitational force and normal force, particularly in different scenarios such as standing on the Earth's surface, in an elevator, or in free fall. Participants explore the definitions and implications of weight, normal force, and apparent weight in various contexts.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant states that when standing on the Earth's surface, gravitational force and normal force cancel each other, leading to no net force acting on the person.
  • Another participant explains that a scale measures the normal force, which is interpreted as weight, and this can vary with different accelerations, such as in an elevator.
  • A claim is made that weight is merely a measurement of normal force and does not directly relate to gravitational force, particularly in free fall where normal force is absent.
  • One participant provides an example involving an elevator to illustrate how normal force changes with acceleration, affirming the relationship between normal force and perceived weight.
  • A later reply challenges the terminology used, suggesting that "normal force" may not be applicable in physics and emphasizes that weight is fundamentally linked to gravitational force acting on mass.
  • Another participant introduces the concept of "apparent weight," distinguishing it from the gravitational weight of an object, particularly in the context of an astronaut in space.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between weight and normal force, with some asserting that weight is solely a measure of normal force while others argue for a more direct connection to gravitational force. The discussion remains unresolved regarding the definitions and implications of these concepts.

Contextual Notes

There are limitations in the definitions and assumptions regarding weight, normal force, and their relationship to gravitational force. The discussion does not resolve these complexities.

RohitRmB
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When i am standing on the surface of earth, there are two forces acting on me
1)the gravitational force towards the center of the earth
2)normal force radially oppt to gravity

as the normal force equals gravity, (that is why i don't sink into the ground or start floating in air), so they cancel each other.
now no net force is acting on me.
as gravity force is canceled by normal force, why do we consider weight rather than considering only mass?
 
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When you stand on a scale, the scale measures the normal force only and records this as your weight (this is why your weight as read on a scale can be different if you are for example in an elevator that is accelerating upwards vs accelerating downwards vs in free fall).
 
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So whenever we measure the weight of any object, we just measure the normal force that is been acted on that object.
it has no direct relation with gravity.
Now is my statement correct "When an object is experiencing a free fall, it is getting accelerated due to gravitational force and it also has mass, still it is weightless since there is no normal force acting.
Thus since weight is only a measurement of normal force, it can not give proper idea about (only gravitational force) that is present, but only give a idea about the net force acting on the object.
 
For example, if I am in an elevator accelerating upwards with acceleration ##a## then ##N - mg = ma \Rightarrow N = m(a + g)## so the normal force is the sum of the gravitational force as well as the ##ma## term due to the net acceleration of the elevator. This ##N## is what is read as my weight. Your statement about free fall and weightlessness is correct.
 
RohitRmB said:
So whenever we measure the weight of any object, we just measure the normal force that is been acted on that object.
it has no direct relation with gravity.

Hi RohitRmB. It would be best to avoid the term "normal force" as that is not an applicable term in physics. Weight is the force attributable to gravity acting on a mass. If there is no force opposing your weight, then you accelerate in free fall. If you are held in a fixed position (e.g., by the platform on a set of bathroom scales), then the dial on the scales registers the force it's exerting to hold you up. If there is a force partially opposing your weight, such as air resistance, then your acceleration towards the centre of the Earth is slowed because of the smaller nett force to accelerate your mass.

There is an equation that defines weight: weight = m x[/size] g
 
Sometimes the term "apparent weight" refers to the weight that would be measured by a scale, i.e. the normal force and "weight" refers to the force of gravity on the object. Using this terminology, an astronaut in the international space station has an "apparent weight" which is 0, but the astronaut's "weight" is about 88% of his/her weight on earth.
 
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