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In a poll of the 50 of the most respected scientists, only one man was on every list at or near the top – Greatest scientist of all time. The birth of physics starts: Isaac Newton had many discoveries, but perhaps his greatest united the earth with the heavens – The law of universal gravitation.
In the 1600’s, everything was a miracle. People believed in magic, curses, astrology and spells. It was commonly to think earth was 6000 years old. And they had other crazy ideas too.
20th century scientists like Einstein and Bohr, and even 19th century scientists like Maxwell had a body of scientific work that they could build upon. They could stand on the shoulders of other great scientists. Newton, however, had almost no shoulders to stand on.
Newton had 4 major accomplishments:
1) Developed calculus
2) Discovered many of the laws of optics
3) Developed the laws of motion
4) Derived the universal law of gravitation
Any one of these accomplishments is Nobel-prize worthy, and would have put Newton among the greatest scientists who ever lived. But to have done all four is staggering.
And, Newton came up with the theoretical basis of all of these accomplishments in a period of only 18 months. Newton published it 20 years later in 1687 – in an epic landmark book of physics called Philosophiae Naturalis Principia Mathematica (filo-sofi-eye Na-tur-alis Prink-ee-p*e-ah Mathematica) or Mathematical Principles of Natural Philosophy.
I believe Newton’s greatest discovery may very well be the law of universal gravitation, which brought together all his other laws of motion.
According to Newton, one fall day on his farm during those plague years, an apple fell at his feet. As he looked at the apple, and looked up at the tree from where it fell, he asked himself what is it that caused the apple to fall? It must be some kind of force from the earth acting on the apple without touching it – Action at a distance.
He had a brilliant insight that it may be the same force acting on the moon, but just with a different magnitude. He reasoned that whatever the force is, it may be proportional the total amount of stuff in the object, all the atoms, in other words its mass.
Newton also guessed that whatever gravity is, since it emanates from all parts of the earth, it must spread out like a sphere in all directions. And if that is the case then it must decrease in magnitude proportional to the surface area of a sphere.
Because surface area is proportional to the radius squared, and since this surface area gets b****r the farther away from earth you are, then the magnitude of this force must decrease by r squared as well. This means that the r squared must be in the denominator.
F = G M1 M2/d^2 — So this completes the formula for the law of universal gravitation. The force is proportional to a constant, now called the gravitational constant G, times the product of the two masses, divided by the distance between the two masses, squared.
So if gravity is pulling the moon, why doesn’t the moon hit the earth? If you have an object moving at a constant speed with no force like friction or gravity acting on it, Newton’s first law says that it will just continue moving in a straight line, at a constant velocity V. There is no acceleration.
If, you dropped that object from rest near something with gravity like earth. It will accelerate towards the earth. If we take an object traveling at a constant velocity while it experiences an acceleration, due to the gravity, it will have a different motion. It will experience a pull towards the earth. And if you take the tiny movements of the object towards earth continuously as it moves, the trajectory of this object will be circular. It will form an orbit. This is how the moon orbits the earth.
Another way to visualize this is to imagine a cannon on top of a mountain that fires a cannon ball at a certain speed. The cannon ball will land at some distance away from where it was fired as it gets pulled toward the earth. If you fire it at a sufficiently fast speed, it will go all the way around the earth and hit the back of the cannon. This is the same way the moon is also falling towards the earth.
Newton also showed that if you fire the cannonball at a somewhat higher speed than needed to just make it orbit in a circle, it will orbit in the shape of an ellipse. The planets orbit the sun in a similar elliptical shape.
#newton
#gravity
#lawofuniversalgravitation
Newton reasoned that this law of gravitation might be universal, not just limited to the earth and the apple and the moon. The idea that everything can be understood using the same principles of motion on earth as well as outer space, changed the paradigm that earth was somehow special.
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