If you understand, you will find differentiation is how much useful in engineering.
Just assume a graph, Differentiation is a rate of change of Y axis quantity, in each point x axis quantity.
Here the blue one is sine, the input wave form
When we do differentiation we are getting red wave, lets see how it is possible
1, in 0 degree the value of blue increases very fast, that yields some value in output wave.
2, in 90 degree the value of blue is no more incrementing or decrementing(no change) so the output is zero.
3, in 180 degree point the value of blue is decreasing very fast, that yields negative value for output.
4, that is how we are getting cos wave form from sine when we do differentiate.
Applications:
simple applications of differentiation is velocity.
The rate of change of distance of a object with respect to time is velocity.
The rate of change of velocity over time is called acceleration.
In electronics,
The current flowing through a capacitor is proportional to the rate of change of voltage on its terminals.
In inductor the induced voltage is proportional to the rate of change of current.
To say actually the applications are countless.