WHAT IS GRAVITY ?

Surprisingly weak yet mysteriously powerful, gravity is the super glue of the universe

Everything in the universe is made of matter the cosmic 'stuff' of creation. Mass is measurement of the amount of matter contained in any object, from planets to protons.

The Earth, for example,has a mass of 5.9742 x 1024 kilograms,while the mass of a single proton is 1.67262158 x 1027 kilograms.

When we think of gravity,we usually think of the gravitational force exerted by massive celestial bodies like the Earth,the Moon or the Sun.But the truth is that any object of any mass-even a sub-atomic particle- exerts a gravitational pull on near by objects.

Sir Isaac Newton proved that objects of greater mass exert a stronger gravitational force.That's why we typically talk about gravity in reference to planet sand not protons.

But the shocking truth about gravity is that even a colossal hunk of rock like the Earth exerts an exceptionally puny pull.An infant,in fact,can defeat the combined gravitational pull of every single atom on the planet by simply lifting a wooden block off the floor.

That's what makes Newton's discoveries so amazing,even today.Gravity-this wimp of a force-is somehow powerful enough to pull the moon in to orbit and keep the Earth cruising in a perfect elliptical path around the Sun.Without the constant tug of gravity,planets would crumble into dust and stars would collapse.

Gravity is also responsible for giving objects weight.But don't confuse weight with mass. While mass is a measurement of the amount of matter in an object,weight is the downward force exerted by all of that matter in a gravitational field.In the zero-gravity vacuum of space, objects are weightless,but they still have mass.

On the surface of the Earth, where the force of gravity is essentially constant,we consider mass and weight to be equal.But that same object-with the same mass-will weigh 17 per cent less on the Moon,where the gravitational pull is weaker.On Jupiter-not the best place to start a diet- that same object will weigh 213 per cent more.