Acceleration of gravity

If you drop an object relatively near the Earth, it will speed up according to the acceleration of gravity (g).
Object speeds up

When you let go of the object, its velocity is zero.

    * Since g = 32 ft/s2 = 9.8 m/s2, the velocity will be 32 ft/s (9.8 m/s) after one second.
    * Because the object is accelerating, the velocity after 2 seconds will be 2 x 32 ft/s = 64 ft/s (19.6 m/s).
    * After 10 seconds, the velocity will be 10 x 32 ft/s = 320 ft/s or 98 m/s.

You can see how the velocity of the object gets faster and faster.
Terminal velocity

Although a falling object will continue to accelerate until it is made to stop, like when it hits the ground, air resistance will slow down that acceleration. Air resistance is approximately proportional to the square of the velocity, so as the object falls faster, the air resistance increases until it equals the force of gravity. The object has reached what is called its terminal velocity.

There have been many calculations on what the terminal velocity would be for a penny dropped from a high building or airplane. Because a penny would probably tumble, the calculations can become highly complex. One estimate is that a penny dropped from a high building will accelerate until it reaches around 230 mph.

Some dispute such a high terminal velocity. A better example of terminal velocity is that of dropping a baseball. Once a falling baseball reaches 94 miles per hour or 42 meters/second, it would remain at the velocity and no longer accelerate.

FROM:   www.school-for-champions.com/science/gravity.htm