Re: Why does it take more ballast to stabilize my helium balloon in cold

Hallo Griffin,

Welcome to physics!

An easy way to get to the root of any problem is to keep on asking why, 
what and how as long as you don't get to a satisfactory conclusion. Let's try 
this approach here.

q1. Why does the helium balloon go up?

ans  Obviously, there has to be a force pushing it up. but we know that 
     the weight of the balloon and the basket acts downwards. so this force 
     has to be stronger than the weight to push it up.

q2. What is this upward force?

ans. This is called the buoyant force. the surrounding air exerts this 
     force on the balloon.

q3. How strong is this force?

ans. This is as strong as the weight of air displaced by the balloon. The forces 
     balance each other if the balloon maintains level flight.

q4. Why do you have to adjust ballast(weight) with a difference of 
    temperature?

ans. The ballast balances this upward force. this force changes with      
     temperature. the ballast must change to keep the balance.

q5.  So why is this force different at different temperatures?

ans. Now we have come to the root of your problem. In q3 I said that this  
    force is as strong as the weight of air displaced by the balloon. Air  
    is lighter when hot and heavier when cold. Therefore, this        
    upward force increases when it is colder, so that you need more weight 
    (ballast) to balance it.

 I hope I have satisfied your curiosity. Let's hope we get together some 
 day and do some interesting experiments with your balloon.