Good gravy its Gravity!

Posted: October 19, 2010 by fonnaguschakra in Science
Tags: , , , , , ,

Gravity…without it stars wouldn’t be born, matter wouldn’t clump together to

This picture taken 20 July, 1969, of astronaut Edwin E. Aldrin Jr. walking on the surface of the moon near the leg of the Lunar Module (ML)

create the planets and we wouldn’t be here to wonder at its usefulness. It’s the reason the planets stay in their orbits and don’t fly off into space and is responsible for the formation of tides. But what is it?

Well for one thing, it’s a lot more interesting than some might think.

Gravity is created by everything in the universe that has mass. That means me, you, the earth, the moon, the sun, and so on. Of course our gravity is very small; the strength of the gravity is related to the mass of the object so for us the earth is the most immediate thing gravity wise. Interestingly gravity is never actually felt directly by either a person or an object. Only the forces that resist gravity, or act apart from it, can be felt by people, or measured by accelerometers. The sensation and force of weight (such as the force of the ground pushing upward on the feet) are the result of these forces.

A more technical definition of Gravity goes as follows: Gravity is one of the four fundamental interactions of nature along with the strong nuclear force (which holds quarks and atomic nuclei together), the weak nuclear force (which causes radioactive decay), and the electromagnetic force (which is responsible for all the phenomena you encounter every day, except gravity). It used to be called a ‘force’ but since Einstein’s theory of relativity it is more properly referred to as a consequence of the curvature of spacetime.

Gravity used to be called a ‘force’ because of Isaac Newton’s theories on the motion of objects and universal gravitation which were all to do with force, mass, velocity and all those other really important but really boring mathematical equations. Basically Newton’s realization was that every massive particle in the universe attracts every other massive particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. As a result his theory of motion and theory of universal gravitation explained the movement of the planets and became Newton’s Laws and his calculations are still in use today. Without them there would have been no moon landing!

But enough with the history you say, tell me something I can use as pub talk with me mates. Well I hear ya so here goes;

A common misconception to do with gravity is to say that astronauts experience

Astronauts experiencing weightlessness inside a 'vomitcomet' - a fixed winged aircraft which essentially nosedives to give the astronauts the experience of free fall

zero gravity when in orbit on a spacecraft but this is not so. The astronauts are actually experiencing ‘weightlessness’ because they are travelling at approximately 25,000 km/h around the earth.

The space journalist James Oberg wrote: “The myth that satellites remain in orbit because they have “escaped Earth’s gravity” is perpetuated further (and falsely) by an almost universal misuse of the word “zero gravity” to describe the free-falling conditions aboard orbiting space vehicles. Of course, this isn’t true; gravity still exists in space. It keeps satellites from flying straight off into interstellar emptiness. What’s missing is “weight”, the resistance of gravitational attraction by an anchored structure or a counterforce. Satellites stay in space because of their tremendous horizontal speed, which allows them — while being unavoidably pulled toward Earth by gravity — to fall “over the horizon.” The ground’s curved withdrawal along the Earth’s round surface offsets the satellites’ fall toward the ground. Speed, not position or lack of gravity, keeps satellites in orbit around the earth.” http://www.jamesoberg.com/myth.html

It is important to note then that when astronauts are hopping around on the moon it is not because there is no gravity, it is because the moon is much less dense than the earth and so has much less mass and therefore pulls with much less gravity. When compared with denser bodies that have a similar volume the moon’s gravitational field may be seen as relatively weak but it still has one.

There is of course so much more to write about this such as; is there such thing as zero gravity?, what is a vacuum?, is anti-gravity possible?, what’s quantum gravity? and what’s the speed of gravity? but there is a lot to take in so for now here’s an interesting thought from Universe Today: “The pull of gravity on the Moon is so low that you could actually fly with wings attached to your arms (as long as you were inside an enclosed dome filled with air at the Earth‘s atmospheric pressure. Wouldn’t it be great to be able to fly around like a bird?” http://www.universetoday.com/19710/gravity-on-the-moon/

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