什么是牛顿第一定律？

Newton's first law states that objects at rest stay at rest and objects in motion stay in motion with the same velocity unless acted upon by an unbalanced force.

The tendency of objects to resist changes in their state of motion is called inertia, which is why Newton's first law is also known as the law of inertia.

When a bus starts moving, passengers fall backward because their inertia causes them to resist the change in motion, and when a bus stops, they fall forward because their inertia causes them to continue moving.