Real life application of calculus

[Eltahawy]

i want a real life application of calculus so that I can understand it

 

[Doug Huffman]

Radioisotope production and burnout in an operating fission reactor.

 

[Alexmer]

Simple motion over time helped me understand calculus better than anything.

 

[phyzguy]

Calculating how much money you have in the bank as a function of time given a starting amount of money and a certain interest rate.

 

[AMenendez]

Everyone likes donuts, so volume of a torus is a pretty good application of calculus.
Let's say you want to know how many calories are in the donut you're about to eat, but you only know the number of calories per unit volume. To find the total volume, you can rotate the cross section of the donut around the center of the empty hole in the middle (in this context, the empty hole is a distance form the y-axis).
This is a pretty typical application of integrating to find volumes by the method of summing cylindrical shells.