Obviously the force of gravity is acting vertically downward.
显然重力的作用垂直向下。
The direction of the force on the upper conductor is downward.
作用于上导体的力的方向朝下。
The force uptown equals the force downward so that the balloon stays at the level.
向下的力与向上的力相等，所以气球就保持在这一高度。副词成对出现，大多表示相反的意思。
The force uptown equals the force downward so that the balloon stays at the level.
向下的力与向上的力相等，所以气球就保持在这一高度。副词成对出现，大多表示相反的意思。
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