Question

Why does the weight of an object in the air differ from its weight in a vacuum (remembering that weight is the force exerted against a supporting surface)? Cite an example in which this would be an important consideration.

Answer 1

It doesn't.

Weight is weight...period. Weight always equals the object's mass multiplied by the gravitational field strength.

Weight ONLY depends on:
1. the mass of the object
2. the environment's gravitational field


When we speak of reduction of weight of an object due to being immersed in a fluid...I highly recommend you speak of that without ever using the word "weight".

Don't call it weight...call it solid support force.

In CONTRAST to buoyancy...the support force that comes from the fluid.


Buoyancy and solid support force both SHARE the support duty to constrain against the object's weight.

We are LESS AWARE of buoyancy because it isn't as visible, it is difficult to measure directly, and it has a bit more uniformity to it than solid support forces.

BUT...if you are careful, you CAN FEEL buoyancy forces. There is a reason why your nerves aren't screaming "i'm falling" when you are floating on water...like they are "screaming" when you actually are in the state of free fall.