It is generally agreed that Sir Isaac Newton did see the apple fall. He simply wondered why it did not fall up instead of down. Gravity was known long before Newton, but no one could explain why gravity behaved the way it did. Apples fall. Tides surge in. Planets circle the sun. What causes this? Because objects attract each other.
Newton 's explanation of gravity is very orderly in which everything is mutually attracted. Albert Einstein brought our understanding of gravity in the universe on a cosmic scale. His view is that gravity abounds in the entire universe. You cannot escape it, continuous and ever present. Although Einstein's explanation is very complex, it is also very precise. Newton's is a very close approximation, but is preferred; it still gets to our automobiles and to the moon.
Gravity is a learned trait. When we first arrive into this world, gravity begins it assault on us. After several months, our muscles allow us to lift our torso and head above the bed in our crib; when the muscles tire, down we go. Later we begin to crawl. Six points of contact: hands, knees and feet. Crawling is a somewhat safe mode of travel, but very slow. Then standing--clutching to everything to maintain balance. Finally the big one. Walking! It takes a while, but we do master it. Our backbones are cantilevers, and our arms are levers; we swing them to maintain balance in order to maximize mobility in one G. If you stumble--loose your balance--gravity is there to remind you of its presence.
Einstein stated in his theory that gravity and acceleration are equivalent. In a recent conversation with Apollo 16 astronaut Charlie Duke, he confirmed that Einstein is correct. If you are in a space craft traveling to the moon and the engines are fired, and you are not strapped in, you will be slammed against the wall. If strapped in, you will feel the acceleration on you body as the engines are fired. The term microgravity is now used to describe the conditions for traveling in space. Why do astronauts appear to float about uninhibited by gravity? Looks are deceiving. They actually are in gravity, just like a sky diver, both free falling toward earth. Because of the speed of the shuttle, it continually misses the earth in its fall as both the earth and the shuttle are moving through space. Orbital mechanics must be very precise in order to maintain the correct elevation above the surface of the earth while in orbit. Apollo 11 did miss its touchdown site by seven kilometers. Scientist determined that the area, the Sea of Tranquility contained a MASCON area. A mass concentration of Basalt is very dense and therefore exhibited a different gravitational influence than predicted. Future missions were corrected for this error and all landed on target.
Gravity is considered to be the weakest force in nature. After all, a child can easily pick up a two pound rock above the surface of the earth and overcome the pull of the planet's entire six billion trillion tons. Gravity cannot be reflected, stopped or slowed; it always attracts, never repels. It is ever present and just doing what it is intended to do. It gives us a reasonable prediction of how to build things, how to move about, what is safe and what is not. Engineers design machinery around gravity. Hydroelectric dams, clocks and almost all mechanical devices must take gravity into consideration in order to perform their intended tasks.
Humans are shaped by gravity as we moved about in one G. We are vertical on the surface of this planet. Creatures in the sea are shaped differently, they are horizontal. Gravity has shaped the destiny of every plant and animal species on this planet and has dictated the shape of our limbs and organs. The influence of gravity keeps us on this planet. It holds our atmosphere in place; it holds the earth together. Trade Earth's gravity field for that of Pluto's, and all would change. Humans would be extremely tall after generations, maybe thirty feet at age sixteen, but too spindly to engage in any sports activities. Bones would be basically hollow and weakened. That's alright, I will take Earth's gravity. After all, I am conditioned for it. It began when I first entered this world, and in the end, it will cause sagging skin and organs, arthritis and a failing heart, you cannot win against gravity. It is ever present.