
Time based animation and gravity
From: Darrel Plant <dplant@moshplant.com>
Subject: Re: Time based animation and gravity  Help!
To: DIRECTL@LISTSERV.UARK.EDU
At 4:07 PM 0700 8/10/00, Martin Pallett wrote:
1. How do you calculate acceleration in a time based
animation?
the basic formula I am using for the linear animation is
newloc = elapsedTime * vector / overallTime + startloc 
thanks to Darrel Plant
but I am stumped when it comes to including the math involved in the
acceleration
Gravity acceleration is itself a timebased formula, the standard
simple form is:
accel (t) = 32 ft / (t * t) (or 9.8m / (t * t) )
That's usually referred to as g.
Acceleration doesn't tell the whole story, though. What's more useful
is the distance travelled in free fall:
distance (t) = g / 2 * (t * t)
or in feet:
distance (t) = 16 (t * t)
Pretty simple. You'll probably want to futz around with the value you
multiply t squared by, unless you've got other animations conforming
to real units, this is probably not exactly what you want.
2. Should overallTime include the time taken for any bounces? or should
it be tacked on afterwards as a result of velocity at impact?
Unless you're making a simulator, just do what looks best.
There's lots of pages on the physics of freefalling bodies. Here's one:
http://www.mathcs.emory.edu/ccs/math190g/ModuleII/ModIIP5.html
