CK-12 Foundation
Ck 12: Physical Science: Einstein's Concept of Gravity
[Free Registration/Login may be required to access all resource tools.] Explores Einstein's theory of gravity and the warping of space-time.
CK-12 Foundation
Ck 12: Physics Simulation: Black Hole
[Free Registration/Login Required] Watch a clock slow down in the strong gravitational field near the event horizon of a massive black hole. A PDF worksheet and a video tutorial are also available. [2:57]