The direction of the acceleration is the direction of the net force.

加速度的方向与合力的方向相同。

The net force is ultimately the sum of the external force and all the internal forces.

合力是最终的总和,外力与所有内力总和。

If there had been a net force, then indeed it would also go down, if this force were larger than this.

如果没有净力，那就不会下降了,如果那个力大于这个。

Newton's second law of motion, net force equals mass times acceleration, tells us that if the acceleration equals zero, the net force must equal zero.

根据牛顿第二运动定律，净外力等于物体的质量与加速度的乘积，因此如果加速度等于零，净外力也必等于零。

Now there is a net force in the same direction as the acceleration down.

此时，有一净外力和加速度同方向。

Now there is a net force in the same direction as the acceleration -- down.

此时，有一净外力和加速度同方向，都是向下的。

And so the net, the sum of all forces on that object There is no net force on that wheel but there is a net torque, and that's why it's going to precess.

所以综合，物体受的所有力,车轮不会受到净力，但是有一个,净作用力，那就是我要推进的。

An object at rest or traveling in uniform motion will remain at rest or traveling in uniform motion unless acted upon by a net force.

一切物体在没有受到力的作用的时候，总保持静止状态或匀速直线运动状态。