# Retardation of a Balloon's Vertical velocity

1. Apr 22, 2010

### Lunar_Lander

Because I am working quite a lot with balloons (still theoretically though), I have come across reports of some balloon flights in the 19th century, which gave balloon ascent speeds of up to 15 m/s and descent speeds up to -40 m/s. I agreed to the comment to that text, that normally balloons would never exceed ascent speeds of 10 m/s and descent speeds of about 6 m/s.

However, I now have received an E-Mail saying that there should be no problem at all that a balloon could ascent or descent faster than 10 m/s. I think that is not possible due to air resistance, and I would like to calculate for an example. If we consider the forces acting, we got the gravitational force acting straight downward, and the lift straight upward. If the balloon ascents, friction will point downward too (in case of descent upward). The relevant formula should be, given that the balloon is a sphere, $$\textbf{F}=6*\pi*\eta*v$$, according to the law of Stokes. Is that correct or should Newton's law be used?

2. Apr 22, 2010

### Staff: Mentor

I'm no help on the calculations, but it would seem that weather baloon launches would provide some of the fastest initial velocities. I googled vidoes on weather baloon launch, and got plenty of hits. Take a look at the 2nd video on the hit list -- initial takeoff velocity looks to be more than 10m/s: