Turn the crank

The other day in my Calculus I class, my professor used the term “turn the crank” whenever we had to solve the derivative[find the limit to be exact but they turns out to be the same, would they?] of some function. At that time, I only figured it means that we can just go a head and apply the theory(principle of derivatives),without the needs to modify the function (as in the case of some functiosn having the form of \frac{0}{0} and  \frac{\infty}{\infty} which is non deterministic), into the function to work the solution.

One example is such:

The question would read:

Find the derivatives of the following function:

f(x) = 2x^2

He would say: “Turn the crank”.

We would just work on it for a minutes and spit out the answer.[ f(x)' = 4x]

It[crank] turns out to be the crank of the Analytic Engine machine designed by Charles Babbage when I watched the videos of Princeton Algorithm I class.

Analytic Engine Machine - Charles Babbage
Analytic Engine Machine

His famous quotes :

Charles Babbage(1864)
“As soon as an Analytic Engine exists, it will necessarily guide the future course of science. Whenever any result is sought by its aid, the question wil arise – By what course of calculation can these results be arrived at by the machine in the shortest time”

So basically what I get out of this is that we just simulate a machine spontaneously applying the rule set to the problem, or we crank the machine, and turn it and turn it, and it is running, running, ….. and voila the problem solved. Well it “guided our way of solving the problem”, but I think it is just the tool.

Oh well, at least I know what my professor really means now.


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