A sine is a trigonometric function of an angle of a right triangle. The sine (of an angle) is the ratio of the opposite side's length to the length of the hypotenuse (the longest side of the triangle).
A sine wave is a repetitive oscillating graph of the sine function. Therefore, as the function of the angle changes (usually by a clockwise rotation of the hypotenuse), the resulting y value follows. It provides a natural upward and downward wave that we're looking for:
It's specific equation is as follows. Let's take a closer look at it and its derivation:
f(x) = a sin (b(x − c)) + d
y = a sin (b(x − c)) + d
y = a sin (b(x − Pi/2)) + d