AVERAGE SPEED VS AVERAGE VELOCITY

To know the difference between average speed and average velocity, first we have to be aware of the following basic stuff.

Distance Travelled :

The total distance covered by an object in a certain time period.

Time Taken Time Elapsed :

The time taken by an object to cover some distance.

Displacement :

Displacement is the distance between the starting point of the object and the final point where the object ended up.

Speed :

Speed is the distance covered by an object in unit time. Speed is a scalar quantity and it means it has no specified direction. Speed refers to how fast an object is moving, or essentially the rate at which the distance is covered.

Velocity :

Velocity is the total displacement of the object in a specified direction in unit time. Velocity is a vector quantity and it means it has a specified direction.

Velocity refers to the time rate of displacement of the object. Just imagine a person who walks for some distance before returning to his original position. Because velocity is the rate of displacement, this motion results in zero velocity. If a person wishes to maximize his velocity, he must maximize the displacement from his original position. Since velocity is a vector quantity, when evaluating it we must keep track of direction.

The main difference between speed and velocity is that speed does not take into account the direction. Because, it is a scalar quantity, and speed depends upon distance travelled, while velocity is a vector quantity which takes into account the direction, and velocity depends upon displacement.

Average Speed

Average speed is distance divided by time interval for the distance traveled.

Average speed = total distance covered/total time

Average Velocity

Average velocity is displacement divided by time interval of the displacement.

Let s₁ be the position of an object at time t₁ and s₂ be the position of the same object time t₂, then the average velocity over the time interval (t₂ - t₁) is defined by

= change in position/change in time

= [s(t₂) - s(t₁)]/(t₂ - t₁)

or

Average velocity = displacement/time elapsed

Example :

A car travels along a straight road to the east for 40 meters in 1 second, then go to the west for 150 meters in 4 seconds. Determine average speed and average velocity.

Solution :

Average Speed :

= total distance/total time

= (40 + 150)/(1 + 4)

= 190/5

= 38 m/s

Average Velocity :

= displacement/time elapsed

= (150 - 40)/(1 + 4)

= 110/5

= 22 m/s

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