PhET Interactive Simulations: Gravity Force Lab
This site, provided by the PhET Interactive Simulations from the University of Colorado at Boulder, allow students to visualize the gravitational force that two objects exert on each other and to change properties of the objects in order to see how it changes the gravity force.
ComPADRE Digital Library: Newton's 3rd Law
This site, sponsored by the ComPADRE Digital Library supporting faculty, students, and teachers in Physics and Astronomy Education, presents a WonderHowTo video that shows how Newton's Third Law of Motion can be demonstrated using a low-friction "sled" and two rubber bands. The video includes a brief description of Newton's third law and explains the reaction force on the sled. Links are provided for other related videos within the site.
ComPADRE Digital Library: Goddard Space Flight Center: Newton's Third Law of Motion
This site, sponsored by the ComPADRE Digital Library supporting faculty, students, and teachers in Physics and Astronomy Education, provides a lesson plan for teaching Newton's Third Law, including activities and exercises. Among the activities are balloon rockets and ball drops. The lesson plan also includes background information illustrating the law.
HippoCampus project: Newton’s Third Law
This site, sponsored by the HippoCampus project of the Monterey Institute for Technology and Education (MITE), provides a comprehensive video on the topic of Newton’s Third Law.