# The Characteristics Of Gravity If gravity ever stops working, incredible things will happen. For instance, everything not attached to the earth flies off into space, all the planets break free from the sun's pull and the universe as you know it ceases to exist. Gravity may never fail, but scientists continue to unravel the secrets of this mysterious invisible force that helps hold everything together.

## Universal Attraction: The Force

Gravity, along with strong nuclear forces, weak decay forces and electromagnetic forces, is one of the universe's fundamental forces It's also the weakest, even though gravity is so strong that one galaxy can attract another trillions of miles away. A well known idea in theoretical physics isn't that gravity is weaker than the other forces, but that we don't experience all of it's effects. That could happen if extra dimensions exist that cause gravity to spread out into those dimensions. Gravity is also the main force that gives structure to stars, galaxies and other massive objects.

## When Obects Fall

Contrary to popular belief, gravity exists aboard orbiting space craft. In fact, the gravitational pull aboard the International Space Station is 90 percent of its value on the earth's surface. Astronauts and glasses of water appear weightless on video because the planet's gravity is making them fall towards the ground, but they never reach the ground because of the trajectory of their orbit. This constant state of falling while never reaching the earth makes it seem as though they are floating. Gravity causes all objects to accelerate at the same rate, falling faster and faster each second. Drop an anvil and a feather from a 30 story building and they would reach the ground at the same time if air resistance did not slow the feather down.

## The Mathematics of Attraction

The acceleration due to gravity is a real entity whose value scientists denote with the lowercase letter "g." In a famous experiment, Galileo discovered a relationship between g and the distance an object falls over a period of time, as shown in the following equation:

d = 1/2 x g x (t squared)

The letter d represents distance fallen and t is the length of time in seconds the object falls. The gravitational force between two objects is proportional to their masses and inversely proportional to the distance that separates them. Use the following equation to compute that force:

F = G x ((m1 x m2)/r^2)

The letter F stands for the gravitational force, m1 and m2 are the masses of the two objects and r is the distance between them. The uppercase G is the universal gravity constant, 6.673 × 10^-11 N·(m/kg)^2. If an object doubles its distance from another, the gravitational force between them does not diminish 50 percent. Instead, the force drops off by a factor of 2 squared -- gravitational force decreases with the square of the distance between two objects.