To learn more about the physics behind how grinding works check out Friction
The 50-50 is an intermediate level trick where the skater scrapes both of the trucks along a ledge, coping, or rail.
When the skater is locked on the 50-50, it means he/she is practically riding on top of the edge,
Whilst grinding the skater has to overcome friction, which slows the rider down.
Some surfaces create more friction than others.
Grinding a slick metal box will have a lot less friction than an old piece of wood, therefore making grinding easier.
Once the rider has overcome the first bit of friction, the grind become's easier.
Once the rider is locked in to the grind on top of the edge. Another force comes into play
This next force is known as motion.The motion or movement in the grind is also known as momentum.
Newton's law declares that now, the body wants to keep going forward and grinding.
To get out of the grind, the rider simply pushes down with the back foot and turns, and absorbs the impact upon landing.
Or you can ollie out or even kick flip out , depending on your level of expertise