Acceleration due to Gravity

Question

Okay so my father and I are having a debate about the acceleration due to gravity. I proposed that the acceleration due to gravity is constant for all falling objects (neglecting air friction in all problems). So an object freely falling out of an airplane will gain velocity with every second. This brought up the matter of sky diving. He believes this is not true, that an object does not gain speed with every passing second, otherwise sky divers would die. Now I said that with sky diving there is air friction and that slows them down a bit, but not to the extent that he thinks. We agree that body position affects the rate of velocity at which you fall. I can't explain to him to make him understand that a freely falling object is constantly gaining speed. Some one help me please.

Answer 1

You are both correct. A human body in free fall in the Earth's atsmophere will attain a a speed that will not increase, this happens when the drag of the air equals the pull of gravity, it is usually around 120 miles per hour. You must teach your father about the differences of falling in a vacuum and falling in an atmospere.  

Answer 2

the speed always remains constant your father is correct so as you are

Answer 3

You're both right, sort of. The acceleration of gravity is 9.8 m/s^2 and in the absence of other forces falling objects would always gain 9.8 m/s of velocity for every second of fall. However, the faster you move through the atmosphere, the larger the retarding force due to air resistance. At some speed (called "terminal velocity") this retarding force is equal to the force of gravity, and an object moving at terminal velocity falls at nearly constant velocity. Skydivers have some control over this: they spread arms and legs to reduce terminal velocity, tuck their limbs to increase it. Naturally, an open parachute reduces terminal velocity to a few miles per hour.