What Causes Gravity?
Isac Newton brought gravity to our attention hundreds of years ago. But do you really understand how gravity wotks, and what effect it has on your life? It's all explained here in simple, layman's terms.
You’ve probably heard the story of how Isaac Newton discovered gravity when an apple fell on his head some 300 years ago. Well, that’s only part of the story. You see, Newton observed that an object dropped from a height, such as an apple, would fall straight down whereas one that was thrown forward would follow a curved path as it fell. Applying this finding to the orbiting planets, Newton theorized that if thrown fast enough, the object (or planet) would circle the earth in an orbit. From this he deduced that the moon is bound in an orbit around the earth because of the pull of earth’s gravity and the planets kept in their orbits by the sun’s gravity.
The above observations gave rise to the formulation by Newton of a precise mathematical description of this universal law:
All objects, small or large, exert a pull on each other, the strength of that pull being dependant on the size of the objects and the distance between them.
Scientists today still use Newton’s formula for such things as sending out space probes. Edmund Halley used it to predict the next appearance of the comet that has come to bear his name. Yet, Newton’s theories were by no means the last word on the subject of gravity.
In 1916 Albert Einstein suggested that gravity not only shapes the universe but also governs the way we see and measure it. He presented this idea in his general theory of relativity. Simply put, if we imagine space to be like a boundless rubber sheet, then placing an object (planet) on that sheet will cause an impression or dimple . According to Einstein the earth, the sun and the stars are like objects on a flexible mat, causing space to curve. If you roll another object onto the rubber sheet, it will be deflected into a curved path by the depression area around the first object. Similarly, the earth, the planets and the stars, move along curved paths, following the natural depressions in space.
The discoveries of both Newton and Einstein demonstrate that laws govern the movements of heavenly bodies and that gravity acts as a bond holding the universe together. Without it, we simply could not exist. It is gravity that holds our Sun together, it keeps our spinning earth in orbit around the Sun and it prevents us from being thrown off as it does so. Without the amazing effects of gravity we, in fact, wouldn’t even be here.