University of Guelph Department of Physics.

http://www.physics.uoguelph.ca/tutorials /fbd/Q.fbd.html

A tutorial on free body diagrams that includes situations involving gravitation, the normal force, friction, push/pull and tensions. Good pictures with overlaid vectors, as well as the same situations reduced to Free Body Diagram (FBD) sketches. There is also a three level graphic-based FBD self-testing quiz which is elaborate but a little slow.

Tutorial written by Mariusz Kovler, School of Physical Sciences, Curtin University, Perth, Australia.

http://www.curtin.edu.au/curtin/dept/phys-sci/
gravity/index2.htm

This tutorial covers a range of topics, including Newton's Law of Gravitation, rotational and satellite motion, Kepler's Laws, gravitational potential energy, and modern physics application of gravitation (Black Holes and gravitational waves.

Online biography, MacTutor History of Mathematics archive, School of Mathematical and Computational Sciences University, St Andrews University, Scotland.

http://www-groups.dcs.st-and.ac.uk/~history/
Mathematicians/Newton.html

Newton's life and work in mechanics, optics, gravitation, and calculus, are described. There is an extensive set of materials describing Newton's theory of gravitation and the calculation of orbits in particular. Additional information on Newton is found in the Rice Catalog of the Scientific Community in the 16th and 17th Centuries.

Virtual Laboratory, University of Oregon, Eugene, OR.

http://zebu.uoregon.edu/nsf/friction.html

A simulation measuring and describing friction between a block and an inclined plane from the Virtual Lab.

IUPUI WebPhysics Project, by Professors Gregor Novak and Evelyn Patterson.

http://www.usafa.af.mil/dfp/
cockpit-phys/cp_home.htm

This is a very complex site which contains investigatory activities, theoretical descriptions and quicktime movies related to learning about forces, Newton's Laws, free fall, and gravitation. The US Air Force Academy's Cockpit Physics curriculum teaches introductory physics via airforce and military applications.