What is derivative ?? Why it is used for?

 Derivative is a mathematical tool, which is extensively used in physics. According to me derivative is  a simple mathematical operation used to calculate the slope of a point on a graph of function.(If the function is continuous and differentiable at that particular point). But this is just the definition or general meaning of it. To understand its practical utility we will also need one more mathematical tool called integration. 

So, For example if we need to find the value of electric field( or force on test charge) on the axis of a circular ring, we can't actually apply coulomb's law directly as it is defined for a point charge, but ring is a continuous charge distribution of point charges, so here the concept of derivative is introduced. We will first assume a point charge(vanishingly small charge)  and apply coulomb's law on it as it is a point charge. After getting a relation/equation for that point charge we can use integration (mathematical tool) such that it defines or locates every point on the ring.

Actually I was not trying to explain, " How to calculate electric force on ring ?", but I was trying to explain the extensive use of this mathematical tools in physics or any math driven science (quantitative evaluation).

Hope you liked my short but simple understanding or application of calculus in life.

My goal is to make very short articles/ blog-post, which actually expresses my ideas about the topic and makes everyone understand the true spirit of topic
.