Author |
Topic: How much does planet earth weigh? (Read 8565 times) |
|
hoferman
Newbie
Posts: 10
|
 |
How much does planet earth weigh?
« on: Aug 17th, 2005, 7:41am » |
 Quote  Modify
|
I am very curious what different methods this community can find to the question: How much does planet earth weigh?
|
|
 IP Logged |
|
|
|
towr
wu::riddles Moderator
Uberpuzzler
Some people are average, some are just mean.
Gender: 
Posts: 13730
|
|
Re: How much does planet earth weigh?
« Reply #1 on: Aug 17th, 2005, 12:02pm » |
Quote Modify
|
It doesn't weigh anything, because it's floating in space.
It also doesn't weigh anything because it can't operate scales, nor does it has any need to weigh things for that matter 
|
|
IP Logged |
Wikipedia, Google, Mathworld, Integer sequence DB
|
|
|
Icarus
wu::riddles Moderator
Uberpuzzler
Boldly going where even angels fear to tread.
Gender:
Posts: 4863
|
|
Re: How much does planet earth weigh?
« Reply #2 on: Aug 17th, 2005, 5:11pm » |
Quote Modify
|
I once read an article by Isaac Asimov called "The Man Who Weighed The Earth", about Cavendish. In it, Asimov bemoaned the terminology, saying that it actually should be "The Man Who Massed The Earth", but that popular usage (including his own colloquial descriptions) required the inaccurate title.
How did Cavendish mass the earth? By measuring G, the constant of proportionality in Newton's Law F = GMmr-2. If M is the mass of the Earth, and R is the radius of the Earth, then the acceleration due to gravity on the surface is GMR-2. The acceleration is easily measured and found to be about 9.81 ms-2. R had been determined to significant accuracy by French scientists some time in the 17th or 18th century. So, it had also been known for some time that GM = 3.97x1014 m3s-2.
Cavendish hung a crossbar from a thin metallic thread of known elastic properties, so that he could measure how much torque was being applied to the bar by the angle through which the bar was deflected from its rest position. This allowed him to measure very small forces. On the ends of the bar he placed as massive weights as the supporting thread could handle without risk of deformation, and placed two other large masses on stands very close by, placed to produce maximum torque from the gravitational attraction. By measuring the resultant force, dividing by the product of the masses, and multiplying by the square of the distance between their centers, he was able to calculate G = 6.67x10-11 kg-1m3s-2. (I'm not sure what accuracy he was able to obtain with this original measurement.)
Dividing 3.97x1014/6.67x10-11 gives a mass for Earth of 5.95x1024 kilograms. (A more accurate value is 5.975x1024 kilograms.)
|
|
IP Logged |
"Pi goes on and on and on ...
And e is just as cursed.
I wonder: Which is larger
When their digits are reversed? " - Anonymous
|
|
|
Eros
Newbie
Gender:
Posts: 7
|
|
Re: How much does planet earth weigh?
« Reply #3 on: Aug 25th, 2005, 10:11pm » |
Quote Modify
|
Weight is relative it depends on Gravitational pull that is acting on the object. So a person will have different weight on moon from what he has on earth. Now for us to weigh Earth it should be put under some standard gravitational force.| hidden: | I think i am deviating from the problem.  |
|
|
IP Logged |
|
|
|
|
RIDDLES SITE
WRITE MATH!
Home 
Help 
Search 
Members 
Login 
Register
Reply
Notify of replies
Send Topic
Print