determining max falling speed

Post by **The Yosemite Bear** » 2006-05-07 02:35am

I know objects fall at 32ft/sec accleration, how does one determine when an iobject reaches it's maximum acceleration and "terminal velocity"

Cyborg Stan · Post by **Cyborg Stan** » 2006-05-07 02:47am

Well, I'm guessing you're using close-to-the-Earth approximations, since you're quoting the 32 ft/sec/sec (corrected for units) figure. In any case, think for a second.

The terminal velocity would be when the object is falling at it's maximum velocity, and would go no further. Acceleration is change in velocity. Thus, at terminal velocity the acceleration would be zero, the force of gravity and the force of air resistance matching each other. At a bit less than terminal velocity, the force of gravity would still be the same while the air resistance would be a bit less, because of the slower speed. So the net force would be a little bit higher. Keep going back and you'll realize that the net force, and thus acceleration would have to be the highest when the object started falling. Naturally, if it were an uneven object it would probably turn a bit, but this is just a simple example.

As for the terminal velocity, that's just when the force of gravity matches the force from the air resistance. This differs for different objects in different configurations, as anyone whose parachute failed can tell you.

Stile · Post by **Stile** » 2006-05-07 02:50am

HI-YAH!!! Google-Fu

+http://hyperphysics.phy-astr.gsu.edu/HBASE/airfri2.html

Dooey Jo · Post by **Dooey Jo** » 2006-05-07 06:18am

A few years back I worked out a formula for calculating the force exerted by a wind of a certain velocity on an object of a certain mass and cross-sectional area. I'd post it to solve for mg = F[wind], but it's pretty much identical to the stuff in Stile's link, so that'd be redundant.

Pretty cool though to see that my formula was actually correct

Post by **The Yosemite Bear** » 2006-05-07 06:18am

I was just tying to figure this out I caught the tail end of a mythbusters where they said that the terminal velocity of a bullet falling could be achieved by dropping it 500 feet, due to air resistance....

Post by **Darth Wong** » 2006-05-07 08:58am

In order to calculate it you'd need the coefficient of drag.