You use geometry for manipulating shapes. You use algebra for doing math with unknown numbers. You use trigonometry for studying triangles, and by extension, waves. So what's calculus for?

**Calculus is the study of change.**

When you differentiate something, you get the derivative, which represents the rate at which something increases or decreases.

Integration is combining derivatives, or minute changes, into a whole result.

Using these, you can handle changing values in anything: acceleration, electromagnetism, money... calculus can handle them all.

Useful, eh?