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Are normal force and apparent weight the same thing? I'll let ya know the context from which I am asking this question:

Is there a normal force on an object submerged in water?

So, from what I gathered from this question, you CAN treat buoyancy as the normal force in fluids. But if that was true, then why don't we treat buoyancy explicitly as the apparent weight in fluids. Why do we subtract it instead.(possible duplicate suggestions :

Why is weight in a fluid not equal to the buoyant force?

Why isn't the apparent weight of a body in a fluid equal to the buoyant force? Why does buoyancy reduce it instead?

Look this is the "context" from which I'm asking the question. You only have to answer them if you think that apparent weight and normal force are the same thing. Then you'd have to explain this particular situation. But if you think otherwise, well, then, case solved. But The question itself is broader than this.)

If they are not the same thing, then could you also please mention if there are separate formulas to find them.( It'd also be helpful if you described their relations with ' the weight we feel ' and ' the weight a weighing scale would read if you were to stand on it ')

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A normal force is simply a force that arises from contact between one object and another object or substance. There can be several normal forces acting on an object. For example, an object on a slope held in place by a wedge will have two normal forces acting on it - one from the slope, the other from the wedge. Neither one is equal to the weight of the object (or its apparent weight if the slope is in an accelerating lift).

Apparent weight is a very specific instance of a normal force - it is the normal force registered by horizontal scales on which the object rests. If the scales and the object are in an accelerating lift then the apparent weight will be greater than or less than the “true” (unaccelerated) weight of the object, depending on the acceleration of the lift.

Buoyancy is another type of normal force which acts on objects partly or fully submerged in a liquid. But it is not the same as apparent weight. If you take a submerged object that is denser than the liquid and rest it on unaccelerated horizontal scales, the normal force registered by the scales will be equal to the object’s weight in air minus the buoyancy force. This is the apparent weight of the (unaccelerated) object when submerged in the liquid.

If the scales (still in the liquid) are accelerated up or down then the apparent weight of the object (as registered by the scales) will increase or decrease. But the buoyancy force stays the same. So this also confirms that buoyancy and apparent weight are not the same - they are different instances of normal forces.

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  • $\begingroup$ But how do you calculate the apparent weight of an object in a particular situation? Is there a specific universal formula for it? $\endgroup$
    – ACRafi
    Dec 31, 2021 at 11:55
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    $\begingroup$ @AbdullahChowdhuryRafi Apparent weight is, by definition, the normal force as registered by horizontal scales. There are formulae for specific situations - if the scales are accelerated; if they are underwater; if they are on the Moon etc. But what if they are accelerated and underwater and on the Moon ? A "universal" formula would be complicated and not very informative - a clear understanding of the underlying principles of Newtonian physics is better. $\endgroup$
    – gandalf61
    Dec 31, 2021 at 12:16
  • $\begingroup$ So you are saying that it varies from situation to situation? That it’s kinda experimental? $\endgroup$
    – ACRafi
    Dec 31, 2021 at 12:31
  • $\begingroup$ @AbdullahChowdhuryRafi Yes, pretty much. Any "universal" formula would have too many factors in it to be useful. For example, apparent weight varies from place to place on the Earth because it is affected by (a) distance from the centre of the Earth and (b) rotational speed, which changes with latitude. $\endgroup$
    – gandalf61
    Dec 31, 2021 at 12:49
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The term “normal force” refers to the perpendicular component of the force from a surface. If there is a scale between the surface and the object under study, then the reading on the scale will give the normal force and the apparent weight. If the object is hanging below the scale, there may be no normal force (or the weight might be shared between the two). Buoyancy is generally treated as a separate force.

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