On 12/5/07, Patrick Mullen <[EMAIL PROTECTED]> wrote:
> Well pong is viewed from above, so downward acceleration makes no
> sense. (ping pong)
So it would be a case where the bounce is sideways, like hockey or soccer.
> As for bouncing indefinitely, pong takes place in
> a magical universe where no energy is ever lost :)
And now, for your random amusement:
Well, some energy must be lost from the ball, and transferred into
the wall, (so the walls should move as well as the ball). That way,
the energy would be temporarily lost to the ball, but then given back
to it when it hits the other wall, which is moving towards it.
Actually, that's sort of what happens. The energy of the ball goes
into the Earth, accelerating it VERY slightly. If collisions were
totally elastic, and friction was zero, the ball would bounce forever.
Either that or the ball must be infinitely light, in which case,
it would be accelerated to the speed of light by a touch. However, as
long as the object it comes into contact with remains motionless, the
bounce will just be a bounce, and not a speed change. (Velocity
changes because the direction does). On the other hand, since the
ball is massless, the ball's velocity can be changed instantaneously.
Because the contact time is nonexistent, the speed of the paddle per
unit of time is irrelevant, so it would always bounce and never
accelerate. Even friction would have no effect. (Air friction,
caused by air molecules, for example, would cause the ball to bounce
rapidly between the atoms- no energy would even be lost as heat, or
would it?).
Note that these two cases only work if the ball has a set speed to
begin with. If it was at rest, a single atom of gas would accelerate
it to light speed. If it was going at light speed, there is no way to
stop it because it would retain the speed of any collision. If it hit
another atom of gas, it could not transfer energy because it does not
have any mass to carry the energy. Or would it? Physics says that
the same force is required to stop a particle as took to accelerate
it. So identical atoms at identical speeds could both stop and start
the ball? However, Physics, as far as I know, does not say what
happens with a particle of no mass.
Now, according to Wikipedia, the mass of a photon is zero. Yet we
know that photons carry energy (shine this:
http://www.youtube.com/watch?v=vXDYCGVEMac into your face (don't)).
Since energy is mass (the conversion factor is the speed of light
squared), photons must have effective mass. Yet they don't! Somehow,
they can obviously be created and accelerated. So, there are your
magic particles, but we don't often see them going slower than the
speed of light, not to mention small, so they're useless for Pong.
Of course, there is a paradox in all this, that the ball can
retain kinetic energy, yet have no mass. It could be viewed that, by
Physics, it could not impart energy with no mass, because energy
transfer is proportional to the mass and speed of an object. But
photons accelerate, at least, so ??? Incidentally, ask someone what
(1/infinity)*(infinity)
is. I want to know.
Best not to analyse it too much. :-)
Ian
