I I fill a school bag with a small amount of helium gas ( in a small, leak proof chamber) and then put books in it , will it reduce the net weight the child has to carry ??
So long as the chamber floats before you put it in the bag.
Helium is lighter than air to the tune of a bit over 1 gram per liter at sea level. A school bag might have a volume approaching 10 liters, so the maximum benefit of the proposed scheme is around 10 grams.
IOW, it ain’t gonna be worth it.
Yes, but if it’s size allows it to be contained in the bag, it will have so little lift the child won’t benefit.
Anyone got any practical suggestions to reduce the weight of the bag ??( apart from carrying lesser books 
)
I’ve seen more and more kids use rolling backpacks, probably due to the concern of heavy backpacks. Probably the best solution, save for tying several helium balloons to the backpack (which may end up being a distraction).
Mythbusters did this one–sort of. If I remember correctly, it took 3500 helium balloons to lift a 44 lb. child.
So only 795 balloons to reduce the pack load by ten pounds - sounds like a plan.
Put the kid on a treadmill?
It will “reduce the net weight the child has to carry.”
ETA: I hope this wasn’t taken with offence… I wasn’t calling your kid roly-poly, I was referring to a long-standing (treading?) reference.
What about that guy who used helium balloons tied to his lawn chair to so flying? IIRC he was cited by the FAA. He had nowhere near that number of balloons.
Nonetheless, I agree that the amount of helium needed to float a backpack would be impractical.
Did you hear about the guy who thought he would get better gas mileage if he filled his tires with helium?
I don’t think he was using party-sized balloons…
True, there were about 45 weather balloons. Not sure how big a weather balloon is, but still, would that translate to thousands of toy balloons?
Weather balloons I’ve seen were maybe 5 or 6 ft in diameter. So that’s 100~200 times more lift than a 1-ft diameter balloon.
What would happen if Sealed Air switched to helium-filled Bubblewrap? Assume for a moment that their plastic is capable of holding helium for an extended period of time, and assume they’re not constrained by economics.
Even if it makes a minute difference per yard of the stuff, how much of it is traveling around the country in trucks and airplanes every day? Would the benefits/differences be cumulative?
Yep, because as already mentioned, you need an awful lot of helium to lift a decent amount of weight (100 cubic feet of helium lifts about 7 pounds). Larry Walters used 45 weather balloons that were each eight feet in diameter. A toy balloon is like a foot (maybe a bit more) in diameter.
Carrying fewer books?
Wait! I know! Let’s compress the helium, so we can get more into the bag! That’s sure to work.
Compress it enough, and we’ll get liquid helium, which is known to flow uphill! It’ll be great!
[sub]yeah, that’s the ticket![/sub]
Attach an airfoil to the bag and have your kid run to school. The faster he runs, the more lift he generates and the lighter the bag becomes!