An object is said to be in motion when its position changes with respect to a reference point. Motion is a change in the position of an object over time. It describes how an object's position changes from one point to another.

Mathematically, motion can be described using the following equation:

$$x_f=x_i+v_it+\frac{1}{2}at^2$$

Where:

- $$x_f$$ is the final position of the object.

- $$x_i$$ is the initial position of the object.

- $$v_i$$ is the initial velocity of the object.

- $$t$$ is the time taken by the object to move.

- $$a$$ is the acceleration of the object.

Objects can be in motion in different ways, such as:

- Linear motion: An object moves in a straight line. For example, a car driving on a straight road.

- Circular motion: An object moves in a circular path. For example, a planet orbiting the sun.

- Rotational motion: An object rotates around its own axis. For example, a spinning top.

The study of motion is called kinematics. Kinematics is a branch of physics that describes the motion of objects without considering the forces that cause the motion.