Calculus is the mathematics of change, and how it can be measured. The concept of calculus can be used in many different ways such as to measure the volume of a 3D object. For example, it can be used to measure the objects with curves such as spheres, cones, barrels, and prisms, imagine you took the object then you cut it into many small disks that's volume can be measured, then you measure all those disks you then have the volume of the full object. Calculus also comes in two main different ideas Derivative Calculus which tells you the speed in which something is changing at and Integral Calculus which is used to tell you how much it is accumulating. The aspect of Calculus over time can be observed in the refraction of light. If a beam need to get from A to B through two different surfaces then it does it in the quickest way possible the longest way for light to travel between these two substances is straight from A to B and traveling straight down and then bending is also long, so light takes the quickest way possible which is to travel at an angle then bend back. The graph attached illustrates the angle that it is to be at as X and T need to be as low as possible.