It is a mathematical fact that the casting of this pebble from my hand alters the centre of gravity of the Universe. 

THOMAS CARLYLE (1795-1881)

Centre of Gravity

Centre of Gravity

The centre of gravity (COG) – also called centre of mass - is the point at which all of the weight of an object appears to be concentrated, i.e. if you’re analysing the effect of gravity on an object you can do so by analysing the effect on this single point. (This insight is attributed to Archimedes (287-212 bc).
For regular objects such as spheres and cubes the COG is situated at the geometric centre of the object, but in an irregularly-shaped object, or one in which weight is distributed unevenly, the COG can sometimes be outside the object - e.g. the COG of a horseshoe is in the space between the two ends.
One way to find the COG of an area is to cut it out and try to balance it on one-finger at two or more points. At each point, the COG will lie somewhere on the vertical line directly above your finger, and therefore the intersection of all these vertical lines from different balance points indicates where the COG is. By cutting out a map of Great Britain, you can find the very centre, which turns out to be on Brennand Farm, about seven kilometres north-west of Dunsop Bridge, Lancashire.


Fosbury Flop

One of the interesting things about the High Jump is how long the current World records have stood. Javio Sotomayor’s 2.45m was set in 1993, and the women’s record of 2.09m has been held by Stefka Kostadinova since 1987. Records have been characterised by technical breakthroughs leading to step changes, rather than incremental improvements: the Scissors, followed by the Eastern Cut-Off (1.97m), then the Western Roll (2.03m), then the Straddle which took the record to 2.28m in 1964. But in 1968 Dick Fosbury won the Olympics using a technique of sliding over on his back and landing on his neck in a way which was made possible (or, at least, survivable) by using landing mats rather than sand pits (in its completed form, anyway – Fosbury actually developed the style as a teenager jumping into shavings).
Fosbury’s result (2.24m) set a new Olympic, though not a new World, Record. Four years later, Fosbury didn’t even make the team - but 28 of the 40 competitors who did were using his technique, and nowadays all of them do. Every world record since 1978 has been set by a flopper. The secret of the technique has as much to do with physics as physicality: the Scissors is very inefficient as one’s centre of gravity (COG) passes some 30cm above the bar. The Straddle is more efficient but your COG still passes over the bar (by about 5cm). But the Flop can actually allow your COG to pass under the bar, which gives you extra height in exchange for no additional take-off power.

The Moon and the Earth both orbit a common centre of gravity located about 1000 miles below the surface of the Earth.

When mounting a mate, an male ostrich spreads his wings for stability.

Moving Your Centre of Gravity Into Orbit

A 44,000 mile tall person would weigh nothing at all, because his Centre of Gravity would be in orbit.
The geostationary orbit is a circular orbit 22,236 miles (35,786 km) above the Earth's equator that follows the direction of the Earth's rotation. Any object in such an orbit is synchronised with the Earth’s orbit and thus appears motionless in the sky, to observers on the ground.
The physics are exactly the same as those that would (theoretically) enable a space elevator to operate. A space elevator is a cable with one end attached to the surface of the Earth near the equator and the other end in space beyond the geostationary orbit. The opposing forces of gravity, (stronger at the Earth end) and the outward/upward centrifugal force (stronger at the space end) would hold the cable taut and stationary above a single position on Earth. In effect, the cable would be suspended from the far end like a plumb line, rather than being supported from below like a tower.

Being able to transport people and equipment into space without using rockets is an exciting prospect and space elevators have found their way into the works of sci-fi writers like Arthur C. Clarke and Robert A. Heinlein. Unfortunately we haven’t yet developed a material light and strong enough to make the cable from, although something based on carbon nanotubes is theoretically possible. 


Opinion is like a pendulum and obeys the same law. If it goes past the centre of gravity on one side, it must go a like distance on the other

In 2005, an astrologer tried to sue NASA for 'upsetting the balance of the Universe'.


You may hate gravity, but gravity doesn't care.