text: free falling speed for object? i'd like to find out what equations are involved for calculating this (including calculating the air resistance) and if possible could you provide an example calculation. you can assume any surface area for the object in question but could we assume the density of air (starting at 10,000 feet). the required input data for this ? is: mass of object shape of object size of object air density = f(altitude)  i assume we are talking about the terminal velocity, which will not actually be constant, but vary with altitude.  the shape and size will determine the drag coefficient, cd.  cd for various shapes are found in aerodynamic texts.  the aerodynamic drag formula is d = cd*(ρv²/2)*a   where ρ is the density, v the velocity, and a is the reference area the cd is based on. the driving force for the motion is simply mg, the weight of the object.  at terminal condition, d = mg, and the above eqn becomes  mg = cd*(ρv²/2)*a  --->v² = 2mg/(cd*ρ*a)  to give you some numbers to play with, the cd of a teardrop shaped object is in the neighborhood of 0.10 based on its cross sectional (┴ to direction of travel) area.  air density @ 10kft = .001758 sl/ft³ and at sea level =.00238 sl/ft³.  you can assign any mass and area you like to put in the eqn.  area is in ft² and mg is pounds.  velocity will be in feet /sec.  good luck!