1. The problem statement, all variables and given/known data A small balloon filled with helium is released. What is it's initial upward acceleration? The only data given is ρ air = 1.29 kg/m^3 and ρ helium is .18 kg/m^3 I assume the bouyant force ( FB ) = the weight of the air displaced by the balloon so BF = W(air) = ρ(air) * g * VolB = MassB * Accel and VolB = MassB / ρ(helium) 2. Relevant equations so Accel = [ ρ(air) / ρ(he) ] * g = ( 1.29 / .18 ) * 9.81 = 70.3 m/s^2 3. The attempt at a solution the answer in the book is 61 m/s^2, and I found that ρ(air) and ρ(he) change with temperature, but I have not been able to get the answer in the book. At ρ(air) 20degrees C, I get Acc = 65.4 m/s^2 which is still too high.