How Does Gravity Work

One of the most important scientific breakthroughs of all times is Sir Isaac Newton's universal law of gravitation, all thanks to the falling apple. Gravity is an invisible force that pulls all matter together. Sir Isaac Newton studied the reason behind the falling apple and defined it as the law of universal gravitation,"Each particle of matter attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them."

Gravity is the reason behind, things staying on the Earth's surface as also for the formation and movement of all the planets and other heavenly bodies.

Standard Formula of Gravity
Gravitational force = (G * m1 * m2) / (d2)
where G is the gravitational constant, m1 and m2 are the masses of the two objects for which force has to calculated, and d is the distance between the centers of gravity of the two masses.

How Does Gravity Work
This is where the standard formula of gravity comes in. Let's consider the two objects; the Earth and us. As we move around the Earth's surface, it pulls us and we pull back. Mass is the amount of matter in any object, since the Earth's mass is more compared to us, we get pulled towards the Earth. Besides the amount of mass, gravity also depends on how far you are from a particular object. This is probably the reason why we don't get pulled towards the Sun, which has more gravity than the Earth.

Zero Gravity
The condition of apparent weightlessness, caused by the resistance of the gravitational force on the body is defined as Zero gravity or Free Fall. This is mostly experienced by astronauts traveling in the orbit.

Acceleration Due to Gravity
Acceleration is caused by a force on an object. A free falling object has an acceleration of 9.8.m/s/s, towards Earth. This numerical value for acceleration is known as the acceleration of gravity and has the symbol g to denote it. Galileo's theory that all things will fall with the same acceleration, in the absence of air was demonstrated 300 years later by the crew of Apollo - 15 on the moon by dropping a hammer and a feather. Since there was no air resistance, the feather fell at the same rate as the hammer.

Newtons Three Laws of Gravity, as translated from the Principia's Latin

Newton's First Law of Motion
Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

This is also called the Law of Inertia and is made up of two points. The first point says all objects will only move as long as there is a force moving it and the second point states that an object will not change its direction and speed until a force acts on it.

Newton's Second Law of Motion
The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.

This law is useful in classical mechanics, it means the change in momentum is directly proportional to the applied force. As mass is constant, the force will result in a change of velocity or acceleration. Since acceleration is a vector quantity, it involves magnitude and direction. So to accelerate, force must be applied to the object.

Newton's Third Law of Motion
Of every action there is always opposed an equal reaction; or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.

A force is an interaction that occurs in object pairs of the same type and same magnitude, in opposite directions and have different effects. Since action and reaction are exerted on different objects, they don't cancel each other.

How Gravity Affects the Plants
A British physiologist A. Knight, in 1806 demonstrated through an experiment, the control gravity has on the direction of root growth. The term geotropism was first coined by A. B. Franck in 1868. It is a growth movement by a plant in response to gravity. Positive geotropism is shown by the roots that grow in a downward direction and negative geotropism is shown by the stem that grows upwards. All other varying directions are called plagiotropic. It is believed that geotropism is caused by Auxins, the plant hormone.

Gravity accounts for the co-existence of the Earth, the Sun and all other heavenly bodies in their orbit. The formation of low and high tide and the varying temperatures are also due to the effects of gravity. Newton's law of universal gravitation has indeed solved the mystery of the fallen apple!