Question

What is average speed and how is it different from instantaneous speed?

Answer 1

Though both the terms appear more or less the same, as physicists we know that they are entirely different physical quantities. You could differentiate between these quantities by simply defining both the terms. You could also mention various similarities present between the two.

Complete step by step solution:
In the question, we are asked to differentiate average speed from instantaneous speed.
The physical quantity that tells you how fast an object is moving at a particular instant anywhere along its path is called the instantaneous speed. It can also be defined as the average speed between two points on the path that the object is moving where the limit is time between these two points approach zero. Instantaneous velocity can be mathematically expressed as,
v\left( t \right)=\underset{\Delta t\to 0}{\mathop \lim }\,\dfrac{x\left( t+\Delta t \right)-x\left( t \right)}{\Delta t}=\dfrac{dx\left( t \right)}{dt}
When a graph of position versus time is plotted, the slope of the tangent line at a particular point will give the instantaneous speed.
Now, let us discuss the average speed. It can be simply defined as the total distance travelled divided by the elapsed time. That is,
$\overline{v}=\dfrac{s}{t}$
Where is the total distance covered and t is the time taken for the same.
However, the dimension of both these quantities, that is, instantaneous speed and average speed is the same which would be the dimension of length per time.
Hence, from the very definition we get the difference between the two.

Note: We another set of quantities that is instantaneous velocity and average velocity. The definitions of these quantities will be very similar to the ones mentioned in the solution. But we know that velocity takes direction into account being a vector quantity. So, average velocity of a motion that starts and ends at the same point is zero as it considers the displacement not total distance covered.