• Question: We are making a balloon powered vehicle that will have a balloon that when the air comes out pushes the air out and pushes the vehicle. will making the size of the hole that the air comes out of make the air go out faster and will this make the vehicle go faster? we have some straws and elastic bands so will putting the straw in the balloon and then keeping it shut with elastic bands work and if so what should the diameter of the hole be to make it go the fastest?

    Asked by dave to Luke on 24 Jun 2014.
    • Photo: Luke Fry

      Luke Fry answered on 24 Jun 2014:

      Experiment Dave!! I believe that is the point of making the cars is it not? That is what we do if we aren’t sure of something, try things! My personal hypothesis would be that the narrower the hole is the slower the car will go, BUT it will go for longer. I could be wrong though!

Comments

  • Photo: Graham

    Graham commented on :

    Dave, that sounds like a fun activity, wrapped up in a layer of maths +science.
    You could…. measure the thrust produced by the balloons escaping gas, using different size “nozzles”. That way you’d find the most power.
    repeating using a stopwatch to time the deflation will give you the “power on” time
    then
    knowing how much thrust ( in grams, or Newtons) you can build a really light chassis ( car frame ) aiming at having the chassis weigh less than the available thrust from the balloon.
    – I’l leave centre of gravity, centre of mass, Dynamic centres calculations alone for now….
    I would have a look at the effect of using a long, thin “sausage” balloon instead of a “round” one, as the thin balloon will have less aerodynamic drag.
    looking at the “10%’s” …. thin wheels help. ( less aero drag, less rolling resistance )
    and finally, if you can, to paraphrase the Legend, Colin Chapman, “add lightness”
    by drilling sensibly sized holes allong all Neutral axis’ you can find, ( and that can support the drilling 🙂 )
    Zooooooooooooooom !
    Hope that helps,
    Graham