Otherwise gravity will pull you back down to the Earth.
2
其中一个是地心引力的力量,这股力量试图把卫星拉向地球,就像一根把卫星绑住的绳子,防止卫星飞远了。
One of them is the force of gravitation (地心引力), which tries to pull the satellite towards the earth and is like a rope which keeps the satellite from flying away.