using System;

namespace Science.Physics.GeneralPhysics
{
	/// <summary>
	/// Gravitation
	/// </summary>
	public class Gravitation
	{
		public Gravitation()
		{
		}
		public Vector ForceOnSecondByFirst(Mass m1, Position r1, Mass m2, Position r2)
		{
			Vector del = r2 - r1;
			Position delr = new Position();
			delr.X = del.X;
			delr.Y = del.Y;
			delr.Z = del.Z;
			Vector f = this.Field(m1,delr)*m2.kg;
			return f;
		}
		public static double Constant
		{
			get{return 6.673*Math.Pow(10.0,-11.0);}
		}
		public static double RadiusOfEarth
		{
			get{return 6378100.0;}
		}
		public Vector Field(Mass m, Position r)
		{
			UnitVector rhat = new UnitVector(r);
			Vector v = (-Gravitation.Constant*m.kg/r.m/r.m)*rhat;
			return v;
		}
		public Vector Field(Mass m, Position positionofm, Position r)
		{
			Vector del = r - positionofm;
			UnitVector rhat = new UnitVector(del);
			Vector v = (-Gravitation.Constant*m.kg/del.Norm/del.Norm)*rhat;
			return v;
		}
		public Scalar PotentialEnergy(Mass m1, Position r1, Mass m2, Position r2)
		{
			Vector del = r2 - r1;
			Scalar s = new Scalar();
		    s.Magnitude = - Gravitation.Constant*m1.kg/del.Norm*m2.kg;
			return s;
		}
	}
}