Motion in a straight line

Distance and speed

Walking a distance of 600m in 5 minutes or 300s does not mean that you moved in a steady 2ms-1 or that you moved along any particular direction. You may have walked slowly, jogged some of the ways, or even stopped briefly on the way.  The average speed of an object is defined by the equation

average speed = total distance traveled/ total time taken

In the above walk, to find out how fast you are moving at any particular instant you need to consider the small distance you move during a small time. So, instantaneous speed can be defined by the equation

instantaneous speed= small distance traveled by an object / small-time taken

when the smalltime gets closer to zero.

When we know not only the speed of an object but the direction in which it is traveling, the quantity being dealt with is a vector. It is called velocity.