themes and issues

Newton’s apple and more

So, we have just discovered the several beneficial effects of the apple; but this fruit is very important also because it let one of the greatest minds of all times formulate the law of gravity, too.

I’m talking about Isaac Newton, an English mathematician, physicist and alchemist. Indeed, according to a tale, while he was sleeping under an apple tree, suddenly a mature fruit fell down and he woke up. The scientist asked himself why the apple had fallen down and, after several studies, he formulated the famous law of gravitational attraction.

This story is actually an exasperation of one episode told by Newton: he was looking out of his window and saw a falling apple; later the same Newton invented this story to demonstrate how he took inspiration from events of every day.

The force of gravity is one of the four fundamental physical forces and is applied to bodies because of their mass.
The word gravity derives from the Latin gravis, which means heavy: the bigger the mass of an object, the greater the G-force that it exerts on it. And while gravity is responsible for the motion of galaxies and planets, it is small in the interaction between the proton and electron in one hydrogen atom. So the force of gravity depends on the mass of objects; it’s present in the Moon, too, but our satellite is smaller than the Earth, so its attraction is lower than that of the Earth: if we wanted to weigh less, we should go on the Moon (but actually our mass wouldn’t change) 😉 .

Indeed the weight of a body is the gravitational force that attracts it towards the centre of the Earth:

P = m X g

where m is the mass of the body and g is the acceleration of gravity: it’s constant and equal to 9,81m/s² on the Earth, while it is 1,67m/s² on the Moon because its mass is lower. So everybody falls to the ground with the same velocity if we don’t consider air friction.

As I wrote, the gravitational force that attracts us towards the centre of the Earth is the same that “attracts the planets” (according to Newton): the Sun is bigger than the Earth so it exerts a bigger G-force. This allows the Earth and the other planets to keep their orbit around the Sun, forming the Solar System.

On the other hand, according to Einstein, gravity is the property of deforming space-time, a concept that mixes those of space and time.

The mass of a body generates a gravitational field that bends the lines of the space-time, so the other masses have to move in these orbits. The orbits are elliptical because gravity bends the lines of space-time, not because of the force of gravity . This theory is included in that of the general relativity and gives an explanation to the “weak points” of Newton’s theory, such as the “strange” movement of Mercury around the Sun.

Surfing the Net, I’ve read that perhaps there’s a link between the Japanese earthquake and the gravitational force exerted by the Moon on the Earth. There’s a period called “SuperMoon”, when the Sun, the Earth and the Moon are aligned and the Moon is at its shortest distance from the Earth. So the gravitational attraction is bigger and this could cause extreme variations of tides (they’re an effect of the gravitational forces exerted by the Moon, the Sun and the rotation of the Earth) that, in turn, cause earthquakes, heavy storms and volcanic eruptions.

Incredible! Starting from Newton’s apple  we have come to talk about the solar system: perhaps this is one of the magical effects of the “Queen of fruits”? 😉

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