Why does the earth not fall onto the sun

This is because the earth is already going very fast. This means the earth is constantly trying to leave orbit and hurtle off into space like a ball attached to a string would if you spun it around. The only thing keeping that ball from going into your face it the speed.

Explanation:

The gravity is the string.

The earth doesn't really slow down because space offers little resistance.

wavelength divides in half and speed stays the same.