Genre: Information/Explanation

When describing the motion of objects in terms of distance , time , and direction , physicists use the basic quantities of speed and velocity . Two terms , two distinct meanings . Yet , not uncommonly , we hear these terms used interchangeably . So , what 's the difference ? Why is it incorrect to use the terms speed and velocity interchangeably ? The reason is simple . Speed is the time rate at which an object is moving along a path , while velocity is the rate and direction of an object's movement . Put another way , speed is a scalar value , while velocity is a vector . For example , 50 km / hr ( 31 mph ) describes the speed at which a car is traveling along a road , while 50 km / hr west describes the velocity at which it is traveling . The mathematical calculation for speed is relatively straightforward , wherein the average speed of an object is calculated by dividing the distance traveled by the time it took the object to travel the distance . Velocity , on the other hand , is more complicated mathematically and can be calculated in different ways , depending on what information is available about the object's motion . In its simplest form , average velocity is calculated by dividing change in position ( Δr ) by change in time ( Δt ) .