Escaping from the Earth
The Earth has a force that pulls things toward itself. We call this force gravity(地心引力). This is something we live with all the time, and we take it for granted and hardly ever think about it. But it is a most important factor in rocket operation and must be overcome if we are to get anywhere in space, or off the ground at all.
Take the throwing of a ball as an example. The harder the ball is thrown, the faster and higher it will go. What is the secret Its speed. If we could throw the ball hard enough it would go up and up forever and never come down. The speed at which it would have to be thrown to do this is known as escape speed. Of course, we cannot throw a ball hard enough because the speed required to escape completely from the Earth’s gravity is seven miles per second, or over twenty-five thousand miles per hour.
Once escape speed has been reached by a spacecraft(宇宙飞船), no further power is needed. A rocket aimed
A. Few spacecrafts complete their flight operations.
B. The Earth’s gravity cannot be overcome.
C. No future power is needed after the escape speed is reached.
D. "Free fall" takes the place of the Earth’s gravity pull.
Escaping from the Earth
The Earth has a force that pulls things toward itself. We call this force gravity(地心引力). This is something we live with all the time, and we take it for granted and hardly ever think about it. But it is a most important factor in rocket operation and must be overcome if we are to get anywhere in space, or off the ground at all.
Take the throwing of a ball as an example. The harder the ball is thrown, the faster and higher it will go. What is the secret Its speed. If we could throw the ball hard enough it would go up and up forever and never come down. The speed at which it would have to be thrown to do this is known as escape speed. Of course, we cannot throw a ball hard enough because the speed required to escape completely from the Earth’s gravity is seven miles per second, or over twenty-five thousand miles per hour.
Once escape speed has been reached by a spacecraft(宇宙飞船), no further power is needed. A rocket aimed
A. To travel as fast as it can.
B. To overcome the Earth gravity.
C. To get away from the air resistance.
D. To have strong power in its operation.
The question of where insights come from has become a hot topic in neuroscience, despite the fact that they are not easy to induce experimentally in a laboratory. Dr. Bhattacharya and Dr. Sheth have taken a creative approach. They have selected some brain-teasing but practical problems in the hope that these would get closer to mimicking real insight: To qualify, a puzzle had to be simple, not too widely known and without a methodical solution. The researchers then asked 18 young adults to try to solve these problems while their brainwaves were monitored using an electroencephalograph (EEG).
A typical brain-teaser went like this. There are three light switches on the ground-floor wall of a three-storey house. Two of the switches do nothing, but one of them controls a bulb on the second floor. When you begin, the bulb is off. You can only make one visit to the second floor. How do you work out which switch is the one that controls the light
This problem, or one equ
A. The brainwave pattern
B. The EEG
C. The right frontal cortex
D. The transformational thought
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