From: Ron Kean (ronkean@juno.com)
Date: Sun Feb 21 1999 - 08:08:33 MST
On Sat, 20 Feb 1999 21:38:08 -0500 Ian Goddard <Ian@Goddard.net> writes:
...
You've
> explained how negative lift can occur but NOT
> how negative lift can accelerate an object from
> 0 vertical velocity to a fall rate faster then
> the fall rate in a vacuum. Please explain how
> negative lift can accelerate an object faster
> than the same object dropped in a vacuum.
>
>
Assume a case where there are two vertical force components: gravity and
net vertical aerodynamic force (which includes vertical drag). If
gravity and the net vertical aerodynamic force each point down, the total
downward force exceeds that from gravity alone, so the object would
initially accelerate downward faster than it would fall under gravity
alone in a vacuum. F = ma.
In practice, as the speed of fall increases, drag will limit the speed.
Things which fall a very long distance through air would be travelling at
terminal velocity for most of the fall. A sky diver reaches terminal
velocity in 3 to 5 seconds.
Ron Kean
.
.
.
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