If we believe the story of the apple falling on Newton's head or not, it certainly started him thinking about what force had been exerted upon the apple, which had been stationary on the branch one moment, and accelerating to the ground the next. Lesser mortals just accepted that if you dropped something, it fell to the floor, but Newton's inquisitive mind and mathmatical ability, was not to be so easily satisfied. He realized that the force called "gravity" must make an apple fall from a tree. Furthermore, he deduced that gravity forces exist between all objects. He found that some objects required more force to move than others. For those who are mathematically minded: the force needed to push an object at a given acceleration rate was proportional to the object's mass. Newton's most famous formula says that the force needed to move an object of a given mass at a specific rate of acceleration, was equal to the product of the mass and the rate. Newton also proposed that an artificial satellite be made to circle the Earth, if it was given enough speed in the correct direction.

Having investigated the Earthly effects of gravity, he went on to look at the planets orbiting the Sun, and he found that the force exerted upon the apple, was the same force that held the Earth in orbit around the Sun. This was the force of gravity shown as:

Gravity is a force of attraction that exists between any two masses, any two bodies, any two particles. Gravity is not just the attraction between objects and the Earth. It is the attraction that exists between all objects.

Saturn's rings which are composed of millions of small ice particles, orbit in circles held in place by Saturn's gravity.

Ocean tides are another effect created by gravity. The Moon's elliptical orbit brings it closer to one side of the Earth than the other, with only 93% of the attraction on the far side as compared with the near side. As the Moon orbits the Earth, it's gravitational pull draws the Oceans towards it causing the sea to rise giving high tides at point A & B and low tides at point X & Y. As the Earth rotates once each day, this means that there are two high tides and two low tides each day, at any one place on the Earth. At certain times the Sun and the Moon are both in line with the Earth.Whenthis happens, there are extra high tides called Spring Tides. At other times the Sun and the Moon are at right angles to the Earth. When this happens their gravitational pull tend to cancel each other out. This produces lower high tides, called Neap Tides.

Despite being the weakest of the forces, gravity is the only really important force on the cosmic scale. Nothing can escape it's attraction, from a knife falling from the dining table, to the galaxies being held together by the attraction of the stars, the dust, and gases within it.