That the car remains in motion is a demonstration of inertia.

3. 汽车保持运动状态是惯性的表现。

A train in motion remains in motion unless brakes are applied.

8. 行驶中的火车将保持行驶状态，除非踩刹车。

His first law states objects  in motion must remain in motion until another force changes that motion.

他的第一定律规定运动中的物体必须保持运动状态，直到另一个力改变该运动。

Momentum is often described as an object’s tendency to remain in motion, but technically, it’s an object’s mass times its velocity.

动量通常被描述为物体保持运动的趋势， 但从技术上讲，它是物体的质量乘以其速度。