University of Colorado
University of Colorado: Ph Et Interactive Simulations: Gravity Force Lab
Manipulate the mass and distance of two objects to see how these properties change the gravity force.
Physics Classroom
The Physics Classroom: Vectors: Inclined Planes
Through examples and interactive practice problems, this physics tutorial helps students understand how forces behave on an object on an inclined plane.
Khan Academy
Khan Academy: Particle Systems With Forces
Applying the forces of wind and/or gravity to a particle system so that the system can apply force to all individual particles. In addition, adding a repeller where all the force vectors have a different direction is illustrated.