/*
   ###########################################################################
   This function computes the gravitational acceleration at the surface of a
   sphere with mass (M kg) and radius (R meters).

   ARGUMENTS:
   Mstr = Mass of sphere in kilograms as a numeric string.
   Rstr = Radius of sphere in meters as a numeric string.

   ERRORS:
   FALSE is returned if either argument is non-numeric.
   ###########################################################################
*/

   function BC_Grav_Accel ($MassKgStr, $RadiusMetersStr, $Decimals=16)
{
// Read mass and radius arguments.
   $M = trim($MassKgStr);
   $R = trim($RadiusMetersStr);

// ----------------------------------------
// Error if either argument is non-numeric.

   if (!Is_Numeric($M) or !Is_Numeric($R))  {return FALSE;}

   $G_UNI = '0.0000000000667430';
   $Q = 50;
   $q = trim($Decimals);

// -------------------------------
// Done.  Return force in Newtons.

   return bcDiv(bcMul($G_UNI, $M, $Q), bcMul($R,$R, $Q), $q);

} // End of  BC_Grav_Accel (...)