Atwood machine
http://www.thephysicsaviary.com/Physics/Programs/Labs/AtwoodLab/index.html
Change masses, friction, measure time
http://www.physicsclassroom.com/Physics-Interactives/Newtons-Laws/Atwoods-Machine
g on different planets
http://www.thephysicsaviary.com/Physics/Programs/Labs/AccelerationOnPlanetLab/index.html
Find your weight
Explore value of g on other planets
Dot pattern for gravity
http://www.stmary.ws/HighSchool/Physics/home/animations3/gravityIntro5.htm