Is apparent weight really apparent weight or just net force?

Question

Is it that in water apparent weight is just net force which is 0 when floating like when we are standing on our floor than our net force is also 0 because normal force cancel outs gravity so we can say that in water weight may differ if we measure weight with a weighing machine as it calculates normal force but not the net force unlike spring balance right?

Answer 1

What is called apparent weight depends on your definition of weight as explained in the post What is actually weight?.

Taking the definition of (true) weight as the gravitational attraction on a body then you can say that the apparent weight of the body is the reading which would be obtained if the body was placed on some scales.

In the case of a body with a fluid around it the apparent weight of the body would be the true weight (ie no fluid around the body) minus the buoyancy force (upthrust / Archimedean force) produced by the fluid surrounding the body.
This means that if you weigh a body in vacuum (no buoyancy force - true weight) using some scales then the reading would be different from a reading taken when the body is in air, water etc, (apparent weight).

With a floating body the net force on the body is zero, ie its apparent weight (reading on scales) is zero, because its true weight (gravitational attraction of the Earth) has the same magnitude and is opposite in direction the the buoyancy force. Often the effect of air is neglected because the density of air is so much less than that of the body but with a hot-air balloon you can think of the apparent weight as actually being negative with the buoyancy force being greater than the true weight.

There are also examples where a scale reading (apparent weight) would alter when the body is accelerating.
For example a body in a accelerating lift or a body in free fall / orbiting the Earth where the body appears to be weightless.
For humans that sensation of a change in "weight" or "weightlessness" is due to the change in the force or lack of force pushing up due to the floor of the lift (normal force) or lack of any sensation that something is pushing up (weightlessness).

Answer 2

Is apparent weight really apparent weight or just net force?

The apparent weight is not the net force. When you stand on a horizontal floor, the net force is zero while the apparent weight equals true weight. Here the true weight is taken to be gravitational pull by the Earth, but the term weight is not strictly defined.

See related discussion where I discuss apparent weight for three cases: (i) object on an accelerating floor (elevator), (ii) object in free fall, and (iii) object in a fluid: How to find apparent weight?

There is no strict definition for the apparent weight - see related discussion: Is there a formal definition for apparent weight? It is defined differently for objects on a floor, in free fall or submerged in a fluid. Note that free fall is actually a form of sinking in a fluid, but with much smaller buoyancy and drag. It is said that the apparent weight is zero when in free-fall and when floating in a fluid.

When an object floats in a fluid, there is a force equal in magnitude and opposite in the direction to the weight. But this force acts over the whole submerged surface, i.e. the force is distributed over a large area. That is why we feel weightless when floating in water.

Answer 3

Apparent weight is force due to gravity (sometimes called “true weight”) minus buoyancy force.

If the apparent weight of an object is greater than zero (i.e. it sinks) then scales and a spring balance will both measure its apparent weight. The scales measure the normal force required to support the object in the liquid whereas the spring balance measures the tension in a spring required to support the object. But both forces have the same magnitude, which is force due to gravity minus buoyancy force.

Apparent weight is not always net force because there may be other forces as well as gravity and buoyancy acting on the object - in which case the net force acting on the object changes but its apparently weight does not.