Crab apples subject to Newton's Law of Universal Gravity
The fable children are taught at junior school about Sir Isaac Newton discovering the rules of gravity because an apple fell on his head is most probably just that, but he did come up with his ‘Law of Universal Gravity’* which is used today.
Gravity is something we take for granted. We seldom give it a thought, and yet all of us are subject to this mysterious ‘force’. Gravity is not a substance, but it is a property of anything with mass. The more mass an object has, the stronger the gravity; hence the moon having only 1/80th the mass of the earth, has 1/6th the gravity of the earth. It is believed by some that all forces of gravity extend infinitely into the universe, but the further away a body is from the earth or any other planet, the less powerful the gravitational force becomes. We stay where we are when standing on the earth by virtue of the fact that gravity exerts a force upon us towards the centre of the earth. Without this force keeping us to the ground, we would be flung into space by the centrifugal force generated by the rotation of the earth.
Without gravity the universe would not exist in its current form; for example, the force of gravity keeps the waters of the oceans where they are, while the sun and moon’s gravitational forces affect the oceans’ waters by drawing them or heaping them up, thus causing the flow of waters causing spring or neap tides. When the moon, sun and earth are aligned, the greatest influence of gravitational forces is exerted on the oceans so as to produce spring tides. Gravity also has an affect upon the pressure of the air we breathe by exerting its force on the particles that constitute it. The higher an ascending object is above the earth’s surface, the lesser is the air pressure exerted upon it. The average air pressure at sea level induced by gravity exerts a force of about 14.7 lbs on every square inch of our body, and if we were in a submersible at the location of the wreck of the Titanic, our submersible would have to withstand a pressure of 6,000 lbs per square inch! From this illustration you can see that water has a mass much greater than air.
From the time of Galileo (1564-1642) and later, Isaac Newton (1643-1727), scientists have been studying the nature of gravity. Much is understood about how it operates and the mathematical ‘laws’ to which it conforms, but to the actual question, “What is gravity?” there are varying theories, but no one proven answer. Meanwhile watch out for the banana skin, otherwise Gravity will have the last laugh.