Isaac Newton introduced the mathematical tools necessary to describe motion into mechanics. One of his great contributions to physics was his three laws of motion. It is very likely that the reader knows, above all, the second, which is usually expressed like this: “force equals mass times acceleration.”
These descriptions, already close to modern mathematics, allow us to do real tricks with pencil and paper. Newton’s laws are still used today in tasks as complex as building bridges or automobiles.
The same laws inside and outside the boat
With Newton’s second law, pencil, paper and a little patience, we can describe motion from two different reference frames. Let’s imagine that one is fixed on the ground and the other is moving at a constant speed, like the boat in our example.
When we do the math, we’ll see that Newton’s second law is identical in both systems: “Force equals mass times acceleration,” both inside the ship and outside of it.
This result would go down in history as Galileo’s principle of relativity, sometimes also called Newton’s principle of relativity. Reference frames that move relative to each other without acceleration are called inertial reference frames. Its extraordinary virtue is that The laws of mechanics are identical in all of them.. To avoid further complicating the terminology, we will call them inertial observers here.
Its extraordinary virtue is that the laws of mechanics are identical in all of them.
