r/EducativeVideos

I wrote an app that lets you draw Magnetic Dipoles for students of all ages.

For the first 100 years after Europeans reached the New World, nobody wanted North America. Spain took the gold and silver of Mexico and Peru. Portugal took Brazil. The French and Dutch chased furs. North America was considered cold, empty and useless. The land that would become the United States was basically the leftover nobody fought hard for.

What happened next was not destiny. It was a chain of accidents, gambles and lucky breaks.

Columbus was looking for Asia and bumped into the wrong continent. The 13 colonies were a mismatched group of religious refugees, debtors and merchants who spent most of their early history arguing with each other. Independence itself was a long shot, won partly because France wanted to embarrass Britain.

Then came the breaks. Napoleon needed cash for his European wars and sold Louisiana for about 3 cents an acre, doubling the country overnight. Settlers stumbled onto gold in California right after the US took it from Mexico. Russia sold Alaska for almost nothing and it turned out to be packed with gold and oil. The Civil War nearly destroyed the whole experiment, but the Union survived and came out industrialized.

By the time the canals were built, the railroads connected the coasts and two World Wars wrecked every rival, America was the last big economy standing. A country nobody believed in ended up running the world.

Newton's 3rd Law is one of the first things you learn in physics. But what if it's not actually a law it's a consequence of something much deeper?
In this video we derive Newton's 3rd Law from scratch using momentum conservation, then ask the question nobody asks in school: where does momentum conservation even come from?
The answer takes us to Emmy Noether's theorem one of the most profound results in all of physics and reveals that every conservation law you've ever learned is secretly a symmetry of the universe in disguise.
But here's the thing. Noether's theorem is only as strong as the symmetries it assumes. And the universe doesn't always cooperate.
What we cover:

Deriving Newton's 3rd Law from momentum conservation
Why momentum is conserved the real reason
Noether's theorem: symmetry to conservation law
Translational, rotational and time translation symmetry
Why Newton's 1st Law and Noether's theorem have the exact same problem
Where time translation symmetry actually breaks and what that means for energy conservation globally

This is the rabbit hole behind the law your textbook treats as obvious.