There is a constant search for means of attaining maximum acceleration;
which is limited by the power source. In any event the procedure
transpires in the following manor:
When grampa pushes grandson on a sled to get it going fast, so that he
can jump on the back and they can get a nice long slide, despite the
short slope; the energy thus transferred to the sled per second
dwindles slightly with increasing velocity, accompanied by a dwindling
of the force, exerted, and the energy transferred to the sled by
When grampa feels that the sled is no longer accelerating or responding
to his maximum effort, he either lets go, or jumps and lands with his
knees on the back of the sled, and whee they _go_.
This limit, or equilibrium, occurs despite the strength of the force
and energy transferred: That's why nothing but light can be accelerated
to, or travel at, the speed of light.