[knarf]

"At 80 psig and 30 F, the density of air is 0.5236 lb/ft3 At 80 psig and 80 F, the density of air is 0.4870 lb/ft3."
SO .. I assume THAT is why light aircraft like to lift off in cooler air ... early morning, f'rinstance ?

That's as far as I could get with my pea brain ... I'm still lookin' for the transition from air to he ... it just magically appeared (in MY way of reading, anyway)

[Pikachu_Dad]

That was because the source that was cut and pasted from was comparing a football filled with air and one filled with helium...

:)

[Pikachu_Dad]

lets see if we can post their calcs without the word wrap.

Calculation of Weight

Weight of Air in Football
= WAir = mWAir = [PfVf/(mV)*Pa] = 9.67 g

Weight of He in Football =
= WHe = mWHe = [PfVf/(mV)*Pa] = 1.34 g

Weight of Football with Air
= WF(Air) = WF + WAir = 421 g = 0.421 kg

Weight of Football with He
= WF(He) = WF + WAir = 412 g = 0.412 kg

Conclusion: The He-filled football is about 2% lighter than the Air-filled football.