Have you ever watched the Sun set? After it sinks below the horizon, Earth blocks your view of it. Even though you know it’s still out there in space, you can’t see it. Any and all events on the Sun remain invisible to you for as long as it is below the horizon. If the Sun suddenly turned purple, you wouldn’t see it happen.
In a similar way, once an object enters the extreme gravity zone of a black hole, the object disappears from view. Even though nothing physically blocks our sight, once the object is beyond the boundary of the zone, we cannot see what happens to it. Events beyond the black hole’s "horizon” are invisible to us. Because of this visual effect, scientists named the boundary the event horizon.
For example, imagine a fluffy snowball and a harder-packed snowball of the same size. The fluffier ball is made of less stuff. Its pull is wimpier than the pull of the densely packed ball.
You can feel this difference when you hold the two snowballs in your hands. Each one presses down on your hand because of the gravitational attraction it shares with Earth. The hard-packed snowball has a stronger attraction to Earth because it is made of more material. It presses more forcefully than the fluffy one. It feels heavier.
What do the differences in the two snowballs help the reader understand about gravity?
Which is the best example of a writer using an informal style?