I accept no theory of gravitation. Present science has no right to attempt to explain gravitation. We know nothing about it. We simply know NOTHING about it.

LORD KELVIN (1824-1907)

Gravity

Earth Sandwich


If you wanted to build a gravity train directly through the middle of the Earth you’d need to find two places that are directly opposite each other (‘antipodal’) and both on dry land. As 70% of the surface of the earth is under water, such pairings are quite unusual - a fact which inspired the 'Earth Sandwich' challenge.
 
The 'Earth sandwich' goes as follows. The American satirist Ze Frank came up with the idea, saying: 'Never before have two pieces of bread been simultaneously placed on the ground directly opposite each other on the globe, thus making an EARTH SANDWICH. The fact that the Earth has never been a sandwich is probably why things are so screwed up.' He challenged his viewers to come up with one. The winners, two Canadian brothers named Jonathan and Duncan, completed the task in 2006 by sandwiching Spain and New Zealand. Unfortunately, they prompted immediate controversy because they used a baguette but didn’t check that the two halves were properly orientated, so the sandwich might have been disqualifiable for being X-shaped.
 
Other possible pairings include Indonesia/Colombia, China/the Falklands, Australia/Bermuda, and Greenland/Antarctica. Sadly, the UK can't join in, as all its antipodes are all underwater. The towns of Peking, Illinois and Canton, Illinois were named in the mistaken belief that they were antipodal to those places in China.
 
Mecca is very nearly antipodal to the Tematangi Atoll (aka Bligh’s Lagoon Island) in the South Pacific, so Muslims there ought to be able to pray in any direction they like – they will be facing Mecca whichever way they face. 

Newton's Apple


Gravity is by far the weakest of the four forces we know about (strong, electromagnetic, weak, gravitational). Even with that limitation, it gives us weight, causes planetary orbits and the very creation of stars, planets and galaxies. Gravitational pressure inside stars forces atoms together to form the elements.
 
Isaac Newton didn't discover the existence of gravity. His contribution was to work out the laws which describe its effects. The term ‘gravity’ was in use to describe the force which gives objects weight before he was born, and great thinkers like Copernicus and Kepler had already speculated about gravitational attraction.

The force of Newton’s originality lay in the fact that he demonstrated it mathematically, proved that it was a universal force, and proved the effects of invisible action at a distance. The source for the story about Newton’s train of thought being set off by a falling apple is none other than Voltaire, who got it from Newton’s niece Catherine – so it’s possible that it’s true. The tree which was traditionally associated with the anecdote stood until 1860.

ALBERT EINSTEIN (1879-1955)

Gravitation cannot be held responsible for people falling in love.

Most astronauts become two inches taller in space. This is due to the lack of gravity.

Gravity Trains


If you drilled a tunnel through the Earth from any point on the surface to any other point and then jumped down the hole (and managed to counteract the effects of friction/drag) it would take you exactly 42 minutes and 12 seconds to get to the other side. When you arrived there you would come to a momentary halt in exactly the right place (i.e. you wouldn’t either shoot out of the hole or remain stuck underground) before starting to fall back through the tunnel in the opposite direction. On the first half of the journey you would accelerate due to gravity, and on the second half you’d decelerate, but your momentum would always take you exactly to the other side.
 
You don't have to go through the middle of the planet; you could achieve the same result if you dug a tunnel from, say, London to Moscow as if you dug a tunnel from London to Paris or Sydney.
 
Of course, this is a merely theoretical possibility on Earth, if only because the planet has a molten core to contend with, as well as an atmosphere which would provide air resistance. A body like the Moon, though, has no molten core and only a very thin atmosphere, so maybe the 'gravity train' would be a practical possibility there. Every trip through the Moon would take exactly 53 minutes, which is longer than the journey on Earth despite the much shorter distance because the moon is much less dense and you'd gain less momentum passing through it.
 

Every time a woodpecker brings its head to a halt, the force is equivalent to 1,000 times the force of gravity.

If you were to open a can of beer in zero gravity, any beer you spilt would float around in spherical droplets.

It is impossible to cry in zero gravity.

JOHN F. KENNEDY (1917-63)

All men can fly, but, sadly, only in one direction.

Gravity is weaker around the Hudson Bay area of Canada than in the rest of the continent.

Ultra-cold helium can flow up hill.

If you could add more mass to Jupiter it would get smaller, as its increased gravity would make the giant ball of gas denser.