a body in motion的用法和样例：
- The tendency of a body in motion to continue in motion along a straight line is known as inertia.
- A body at rest remains at rest and a body in motion continues to move at a constant speed in a straight line unless acted upon by an external force.
- A body at rest remains at rest, and a body in motion moves with uniform speed in a straight line, unless a force acts on it.
- A ghost?A body in search of a soul?
- We see bodies in motion here and there.