Our senses are designed specifically to not take notice of things, when those things are omnipresent. All sensory systems exhibit adaptation - if you walk into a room and smell it, you are unlikely to notice ten minutes later. The brain is designed to focus attention on changes in its environment. We get stuck in certain thought patterns based on the contexts in which we live, because they comprise our everyday experience.
We are designed to take things for granted, and so we do. This is one of the reasons Newton's discovery of the law of gravitation was so spectacular. He had to break with one of the most fundamental parts of our daily lives to realize that what he saw in front of him was the same thing that governed the heavenly bodies in space.
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Almost 150 years earlier, the entire world still took for granted that the Earth sat motionless at the center of the universe [geocentrism]. The Sun revolved around the Earth. Everyone 'knew' that this was reality. But in 1543, Copernicus published his
'On the Revolutions of the Heavenly Spheres,' in which he tabulated over a thousand years of astronomical data to show evidence that the Sun was indeed the center of our solar system [heliocentrism]. This was such a gigantic mind-shift in the populace that it is considered the catalyst for the scientific revolution. All based on his use of mathematics to revolutionize what everyone took for granted.
Copernicus gave us a completely new vision of our place in the universe, and its workings.
Galileo worked with this data almost 70 years later; still heliocentricity was not the common view, as it disagreed with many things the Church took for granted. But, with a telescope that he built himself, he noticed Venus, and could see it in all of its phases [just like the moon]. This, along with his discovery of four of the moons orbiting Jupiter, lent a new slew of evidence for heliocentricity; this created such a revolution that he was under house arrest for the last years of his life. Scientists don't have it good in our culture now, but we're doing better than we were! Here Galileo, one of the first real 'scientists,' shows us a fundamentally new truth about the universe, one that impacts every one of our lives on a daily basis [whether conscious or not], and he was forced into isolation for it.
In both of these revolutions, at one point in history there was a single person on this planet with a new, ultimately life-changing piece of information. How slow this information used to spread, before the internet!
Galileo had shown more evidence for the heliocentricity of the solar system, but still no one understood why these bodies moved around in quite the way they do.
The genius of Newton was realizing that when you drop an apple, it falls because of the same reason the moon stays in orbit. People saw things falling for 200,000 years before anyone realized this was true!
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Newton's law of universal gravitation says that every two things in our universe with any mass attract each other. This means the Earth is pulled toward the Sun, and the moon toward the Earth, but also that you are being pulled to your computer screen as you read this. And you are being pulled towards stars millions of light years away.
The big leap in logic is the realization that when an apple falls, it falls because the Earth and the object are pulling -each other- with the same exact force. Now, since the Earth is about a trillion times the mass of the apple, it moves a trillionth as much, but it does move toward the apple!
Aerodynamics is one aspect of falling objects that makes universal gravitation seem so complicated. It predicts that any two objects will fall at the same speed, because they are pulled with the same acceleration (g, about 10 m/s) toward the surface of the Earth. But in reality, objects fall at completely different speeds, because they fall through the medium of air, which creates a huge amount of drag. In some sense, these more advanced topics of aerodynamics required understanding before gravitation could be fully understood - this fact still causes many problems in introductory physics, since dropping a feather and a stone next to each other do not seem to follow the universal law of gravitation!
The discovery of the universal law of gravitation revolutionized our understanding of the world just as Copernicus and Galileo had done before - but what Newton showed us is that the laws governing the far off world of space are the same that govern our behaviors at home.
In some sense, the first scientific question we ever asked is: "Where are we?" and it is a question we are still working to answer.
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Try this at home: If you have kids and haven't watched the show yet, drop some things from different heights of different weights, and talk about why they fall at different speeds, and in fact, why they fall at all! How do these objects falling relate to the moon holding itself in orbit around the sun?
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