1. The problem statement, all variables and given/known data NASA’s Vomit Comet simulates zero gravity by flying parabolic arcs of radius r and speed v to stimulate free fall. If the pilot flies a parabolic path which has a radius of 1km, calculate the speed (*in km/hr) the plane must travel at in order to stimulate free fall? 2. Relevant equations a = v^2/r 3. The attempt at a solution I get the answer as 356km/hr which I think is correct. I solved for v and used 1km for r and plugged in 'a' at 9.81 m/s^2 as freefall is when the only force acting on an object is gravity. However, after thinking about the problem I don't understand how this works in real life at all! I don't understand how you can assume the centripetal acceleration is 9.81m/s^2. If the plane is coasting through the air at any finite speed then surely due to its design if must experience lift so how can you make the only force it experiences gravity when you will always have some lift?