```
v = dx/dt
```
where:
* v is the velocity of the object
* dx is the change in the object's position
* dt is the change in time
If v is zero, then the object is not moving. If v is positive, then the object is moving in the positive direction. If v is negative, then the object is moving in the negative direction.
For example, if a car is driving down the road at a constant speed of 60 miles per hour, then its velocity is 60 mph. If the car slows down to 30 mph, then its velocity decreases to 30 mph. If the car stops completely, then its velocity becomes zero.
It is important to note that motion is relative. This means that the motion of an object depends on the frame of reference in which it is observed. For example, if you are sitting in a train that is moving at a constant speed, then you will not feel like you are moving. However, if you look out the window, you will see the trees and buildings moving past you. This is because you are observing the motion of the train from the frame of reference of the ground.
In conclusion, an object is in motion if its position changes over time. The velocity of an object is a measure of how fast it is moving and in what direction. Motion is relative, which means that it depends on the frame of reference in which it is observed.
