But how does it change that constant velocity?

但是力是如何改变速度的呢？

Or you actually could say an object with constant velocity will stay having a constant velocity

具有恒定速度的物体将一直以这一恒定速度运动，直到有一合力作用于这一物体上。

So now we're dealing with a scenario where the block has a constant velocity.

假设物块向下具有不变的速度假设物块向下具有不变的速度。

And so the constant velocity, v, is equal to-- I don't know.

假设速度v等于5米/秒 方向沿斜面往下。

And for the sake of this video, we'll assume that that constant velocity is downward.

假设速度v等于5米/秒 方向沿斜面往下假设速度v等于5米/秒 方向沿斜面往下。

And now instead of assuming that this block is stationary, let's assume that it's moving with a constant velocity.

假设它以匀速运动，假设它以匀速运动。

200 meters. 50 meters. Constant velocity.

200 米。 50 米。恒速。

Whether that means they’re standing completely still, or moving at a CONSTANT velocity.

这是否意味着他们完全静止不动， 或以恒定速度移动。

Whether that means they're standing completely still, or moving at a CONSTANT velocity.

这是否意味着它是静态的 完全，或者它以恒定的速度移动。

The other was that light travelled in a vacuum at a constant velocity, regardless of the motion of its source.

另一个是光在真空中以恒定速度传播，无论其光源的运动如何。

If the box has no acceleration (it's standing still, or moving at a constant velocity) they'll also add up to zero.

如果盒子没有加速度（如果它是常数 或以恒定速度移动）也将加到零。

It tends to concentrate on disproving one or other of Einstein's grandiose assumptions: the impossibility of determining absolute motion, and the constant velocity of light.

它往往集中于反驳爱因斯坦的一个或另一个宏伟假设：确定绝对运动的不可能性和光速恒定。