2
$\begingroup$

So the air density in Denver is 1.0 kg/m^3. And heated air has the density of 0.95 kg/m^3. So adding the weight of the basket and balloon I don't understand how a hot air balloon could get off the ground. In addition they boast to going 1 - 3 miles up! What am I missing here?

$\endgroup$
6
  • $\begingroup$ Did you mean density instead of pressure? $\endgroup$
    – David Z
    Feb 27, 2015 at 0:09
  • $\begingroup$ LOL just changed that, yes I did $\endgroup$ Feb 27, 2015 at 0:10
  • $\begingroup$ We have no idea what you are missing here, because you did not tell us what you did, or what the weight of the basket or ballon are. That said, there is no reason to believe there's anything but buoyancy at work here. $\endgroup$
    – ACuriousMind
    Feb 27, 2015 at 0:13
  • $\begingroup$ What's so special about Denver that their hot air balloon rides are so interesting? Or, another way, what makes Denver an interesting case compared to anywhere else in the world? $\endgroup$
    – Kyle Kanos
    Feb 27, 2015 at 1:25
  • 1
    $\begingroup$ I suppose Denver can offer hot air balloon rides because their population includes at least one person that owns a hot air balloon and is willing to give people rides in it $\endgroup$
    – Jim
    Feb 27, 2015 at 15:50

3 Answers 3

3
$\begingroup$

Given the imprecision in these numbers, that means that you can lift anywhere between 0 and 0.1 kg per m^3 of air. Per Wikipedia, a typical hot air balloon holds 2,800 m^3 of air in the envelope, so it can suspend something between 0 and 280 kg in the basket. A typical human weighs under 100kg, so you could probably lift between one and three people with a typical balloon, or more people with a larger-than-average one.

$\endgroup$
1
$\begingroup$

So I found the answer....I was not taking the final step of multiplying The difference in density between the surrounding air and the heated air and then multiplying by the envelope volume. I was just focusing on the difference and getting stuck there. I chose Denver because it's a mile above sea level with a known air density. I could have chosen Mt Everest with a density of 0.5 just as easily. So anyway the answer to my question was the Net Buoyancy Force Equation. Sorry if that was obvious to all of you but these concepts don't come naturally to me :)

Thank you for your time

$\endgroup$
1
$\begingroup$

There's no uniform density of heated air. It depends on the temperature (higher T -> lower density) but also on the ambient air pressure.

In Denver, cold air is less dense, because the ambient pressure is lower. But this same effect also increases the density of hot air, by the same percentage.

So, the result is that the lift of a balloon decreases with ambient pressure. Assuming the balloon itself doesn't change weight, the net paylod weight decreases even more. But the payload still can be positive if the balloon's lift exceeds the balloon's weight.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.