| When an object like a penny
falls, it falls at an accelerated rate until Terminal Velocity is achieved. At Terminal Velocity, the downward force of gravity (Fg) equals the upward force of drag (Fd). Illustrated on the right hand side. This drag Force is defined simply as " resistance of an object in a fluid environment such as air or water" ("Drag Coefficient" Answers.com). Drag can be calculated as well based on the formula:  p is air density (mass per volume), A is area, and V is velocity. Terminal velocity takes this into account with the formula: Fg = D - ma, where Fg is the force of gravity on an object, m is the mass, and a is acceleration. This Fg is then plugged into the terminal velocity equation:  Using the values from aerospaceweb.org, which also ran through the same "penny drop" calculations, we can get the value for terminal velocity. These values are tabulated below (10). |
,
|
| Gravity | 9.81 (m/s) |
| Penny's Mass | 0.0025 Kg |
| Density | 1.225 (kg/m^3) |
| Drag Coef. | 1.17 |
| Area | 0.00028 (m^2) |
So the calculated value for Terminal Velocity is: 11.06m/s.
Calculate terminal velocity at NASA link:
http://www.grc.nasa.gov/WWW/K-12/airplane/termv.html
Click to discuss the complications with these calculations ...
Pic from Wikipedia: Drag Velocity Pic (15).
All equations found in "Fundamentals of Physics" 8th Ed.