Gravitational Constant (1 Viewer)

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to me, its just a number with a symbol "G"

but does anyone know how they got it????

 

[underthesun]

6.67 x 10^-11?

I think newton got it the same way as how planck got his constant.. using some strange technique.

Here's how they do it. They draw a paper with numbers 0, 1 , 2 , 3 , 4 , 5 all the way til 9. They then hold a pen, close their eye, and just move the pen / inkpen all the way through the page. The numbers that were crossed by the line were then taken.

Einstein must have gone through many 0s, and got a surprisingly small number. Because of this "phenomena", he thinks the number is special. It turns out it fits with all the motion equations.

Im not sure about planck, but this is a rumor i heard from a very trustworthy person.

 

[underthesun]

Im not quite sure whether you're required to talk about the G constant in the syllabus, really. In my second thought, because Einstein compared his gravitational and centripetal force equations with kepler's law, it could be that kepler was the first to take the constant (after doing the above technique)

 

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edit: that technique, u for real?!?!?!?!?!?!?!?

i was just wondering how they got it...thats all

 

[underthesun]

no man, i was just joking

 

[wogboy]

lol nice technique underthesun, maybe you can try it to predict your UAI

It was some eccentric Britich physicist & chemist that first figured out the value of G, called Henry Cavendish. He used a torsion balance (a dumbell mass hung on a string), and brought a heavy mass near the end of it. Due to the gravitational attraction, the string started to twist very slightly, and this can be measured by lasers. Read here for full details:

http://physics.usask.ca/~kolb/p404/cavendish/

Because gravitational attraction is so weak, G is one of the least accurately known physical constants.

 

[Affinity]

what are the others dubious ones?

 

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????

i was interested coz its in the syllabus, explain the escape velocity in terms of gravitation constant, i'm stuck on that...anyone enlighten me??

 

[underthesun]

It was something along the line of sqrt(2GM/r), right? (cant recall the formula)

Hence, the less mass the planet has, and the bigger the radius of the planet, the less initial velocity it is required to escape the planet (projectile). Im not sure about ignoring air velocity, forgot that part. Dont think that's involved in it though..

 

[underthesun]

Oh and im not quite sure on what much you have to say about the gravitational constant. Maybe, that it is involved in the equations? I have no idea..

 

[Huy]

Originally posted by underthesun
It was something along the line of sqrt(2GM/r), right? (cant recall the formula)

Yep, that's right

More info:

ESCAPE VELOCITY

If an object is projected upward with a large enough velocity it can escape the gravititational pull of the Earth (or other planet) and go into space. The necessary velocity to leave the Earth (or other planet) is called the escape velocity.

Ve = sqroot (2GMe/Re)