This program shows a ball the travels in the path of an ordinary sine curve. That alone is nothing special. This program does demonstrate two key features: scaling and constant speed.
The graphical display area is scaled to the ratio of 1 mathematical unit equal 100 pixels. This is what geographic maps do: scale the earth to a ratio such as 1 mile equal 2.0 inches.
The ball in this example moves at constant linear speed. To move at constant speed everywhere is actually difficult to achieve except in simple paths such as straight lines and perfect circles. For objects moving in other shaped paths constant linear speed is difficult to do. This program will show how to modify delta_x and delta_y continuously during runtime in order to achieve the goal of constant speed.