Black Holes




A black hole is a region of space-time from which nothing can escape, even light. This may sound strange, but it is possible. To see why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is traveling when it leaves your hand, and the higher the ball will go before turning back. If you throw it hard enough, it will never return because the gravitational pull will not be able to bring it back down. The velocity, or speed, the ball must have to escape is known as the escape velocity. Earth's escape velocity is about 7 miles a second.
As a body is crushed into a smaller and smaller volume, the gravitational pull increases, and the escape velocity gets bigger. Things have to be thrown harder and harder to escape. Eventually, a point is reached when even light, which travels at 186 thousand miles a second, is not traveling fast enough to escape. At this point, nothing can get out as nothing can travel faster than light. This is a black hole.
8
Which of the following is a good summary of the passage above?
A.
If you throw a tennis ball really hard, it will travel very fast when it leaves your hand. The faster it travels, the higher the ball will go before it turns back to Earth.
B.
Velocity is also known as speed. To escape gravity, an item has to go at a high escape velocity. The smaller an object is, the higher its escape velocity must be.
C.
Light travels faster than anything else in the universe. The speed of light is about 186,000 miles per second. That is not fast enough to escape a black hole, though.
D.
A black hole is a special region in space and time. Nothing can escape from a black hole, even light, because the escape velocity of a black hole is extremely high.