From YouTube, produced by Phil Plait
This is a live video chat. The narrator was asked, “Why do black holes have such stronger gravity than the stars they formed from?” Here's the answer, gravity depends upon two things, the mass of the object and how far away you are from it. The mass of a star when it collapses the core forms a black hole, so now you can get closer to it and the gravity draws you in. Video is somewhat confusing - the narrator speaks fast and may be hard for young students to understand. Run time 04:11.