when u replace a balloon with less dense hydrogen, does the bouyant force on the ballon change if the balloon?

Question

remains the same size? Explain.

Answer 1

Not sure if I understand. You're going to replace the old hydrogen with some new hydrogen that's less dense? The only way for the density of hydrogen to be less is if the pressure is lower or the temperature is higher. Since this is a balloon, the pressure has to match the pressure of the atmosphere.

So I'll assume the new hydrogen is at a higher temperature. In that case, the balloon can be kept inflated to the same size with fewer molecules. Therefore the mass of the hydrogen will be less because there is less of it. So the bouyancy will increase. The balloon as a whole is less dense so it is more bouyant.