Re: Explain the principle of friction in snowboarding.

I don't think there's a simple answer to this question - friction tends
to be a part of physics that's poorly understood in any sort of general
sense.  But let's look at some possibilities.

The simplest treatment of friction is often taught in introductory
physics.  Here, the "sliding" or dynamical frictional force is
proportional to the normal component of the gravitational force exerted
by an object on the surface.  "Normal" means perpendicular: if the
surface is flat on the ground, the normal force from gravity is
maximum; if the surface is vertical, the normal force from gravity
is zero.  For a hill, it's somewhere in between.

So, in this simple case, when you're sliding down a hill there are
two forces acting on you.  The first is gravity, which pushes you
down the hill, with a total force proportional to your mass.  The
second is friction, which pushes in the opposite direction.  BUT,
because (in the simple case) the frictional force is proportional
to the normal component of the gravitational force, it also is
proportional to your mass.  Therefore, if you plug all of this into
the equation F=ma, and solve for the acceleration, all of the masses
cancel out.  The heavy and light snowboarder get to the bottom at
the same time!

But real life is rarely so simple - the above is an approximation
to the force of friction that works in many cases.  The situation
with snowboarding sounds complex to me.  For example, the heavier
snowboarder will sink more deeply into the snow, which may result
in more resistance since he has to push more snow aside.  On the
other hand, the heavier snowboarder also packs the snow more, which
might lead to less friction.  How all of these things come together
is difficult to say, and probably depends on the particular
circumstances (like how powdery the snow is).  There may not even
be a general answer: sometimes the heavier guy might make it to
the bottom first, sometimes not.  Maybe the best thing to do is
get on a hill and try it . . .