<P> To have a constant velocity, an object must have a constant speed in a constant direction . Constant direction constrains the object to motion in a straight path thus, a constant velocity means motion in a straight line at a constant speed . </P> <P> For example, a car moving at a constant 20 kilometres per hour in a circular path has a constant speed, but does not have a constant velocity because its direction changes . Hence, the car is considered to be undergoing an acceleration . </P> <P> Speed describes only how fast an object is moving, whereas velocity gives both how fast it is and in which direction the object is moving . If a car is said to travel at 60 km / h, its speed has been specified . However, if the car is said to move at 60 km / h to the north, its velocity has now been specified . </P> <P> The big difference can be noticed when we consider movement around a circle . When something moves in a circular path (at a constant speed, see above) and returns to its starting point, its average velocity is zero but its average speed is found by dividing the circumference of the circle by the time taken to move around the circle . This is because the average velocity is calculated by only considering the displacement between the starting and the end points while the average speed considers only the total distance traveled . </P>

Is speed the same as velocity or acceleration