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Re: [pygame] Why does my ball vibrate?



Hi,

On Nov 30, 2007 9:30 AM, Greg Ewing <greg.ewing@xxxxxxxxxxxxxxxx> wrote:
> Matt Smith wrote:
> > I can't quite get my head around WHY the ball sinks into the ground if I
> > don't set ypos back to 384 but it certainly works.
>
> It's probably because you're applying gravity to the ball
> even when it's touching the ground. So it repeatdly gets
> accelerated downwards for one time step, then moved back
> up to ground level.
>
> In real life, when the ball is touching the ground, the
> downward force of gravity is balanced by an upward force
> from the ground, so the net acceleration is zero. You
> can model that by only applying gravity if the ball is
> above ground level.
>

I believe this is the most reliable solution.
(AFAIK there is no upward force though; it's more to do with the
pressure the object exerts being insufficient to penetrate the ground.
So for a simple physics simulation, this solution is also more
correct.)

Matt: I assume you didn't mean to use a suggestive subject line, Every
time I look at my mail I see this conversation, read the subject line
rather differently than you intended, and delete it. And then someone
posts another reply, so it appears again.. ._.