Consider four scenarios:
(on a typical weighing scale)
- Measure the weight of a canister of air filled at atm pressure
- Measure the weight of a compressed canister of air
- Measure the weight of a canister with no air inside.
- Measure the weight of an empty canister on earth with no atmosphere
I would guess that 1 is the same as 4 and 2 and 3 weigh the same as the mass 2 plus the added or subtracted mass of air. Any explanations? This is just because a canister's volume doesn't or shouldn't change the force of it's weight being applied to the weighing scale. A weighing scale accounts for air pressure as it's applied equally on all sides and the machine is tared. When the canister is compressed the air is now heavier and tries to sink. I want to explain this more mathematically in terms of pressure resulting in a greater force on the scale. As you can probably tell, my reasoning doesn't hold much weight at the moment. (not sure if pun intended)