Nib asked, and Nib — askNib's tutor — drew the answer live at a whiteboard. This is the spoken transcript; enable JavaScript to watch it drawn.
What is a black hole, and what would happen if you fell in? (for a curious adult who has not studied physics). Cover, in this order: What is a black hole?; How can gravity be strong enough to trap light?; How does a black hole form?; What is the event horizon?; What happens if you fall into a black hole?; If nothing escapes, how do we see black holes?; Do black holes really suck everything in?; Can a black hole die? — page 2: Gravity that traps light
Throw a ball up and gravity hauls it back. Throw harder, it climbs higher. Gravity never stops pulling, but its grip weakens with distance.
Throw fast enough and the ball never comes back down. That threshold is escape speed, about eleven kilometers every second for Earth, so rockets must be enormous.
Escape speed rises with a body's mass and with how close you start to its center. The Moon needs 2.4 kilometers a second, Jupiter about 60.
Imagine crushing Earth smaller, same mass. Your surface is now closer to the center, so escape speed climbs. Keep squeezing and it nears light speed.
Light is the speed limit of the universe. Squeeze mass until escape speed beats light, and even light can't get out. That's a black hole.
A black hole isn't magic: it's escape speed pushed past the speed of light, so even light falls back.