jan 1, 1687 - Isaac newton published the three laws of motion

Description:

The three laws of motion: 1. Every object in a state of uniform motion will remain in that state of motion unless an external force acts on it.
2. Force equals mass time acceleration.
3. For every action there is an equal and opposite reaction.

I believe this was Sir Issac Newtons greatest accomplishments because it finally gave a understanding for gravity.