Rearding Gravitational force

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mankavada
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Rearding Gravitational force

Post by mankavada » Thu Jan 06, 2011 9:05 am

Hello,
I am a new to this forum and I have a 'very basic' question regarding the gravity or gravitational force.

There is a gravitational force between Earth and Moon. That means both, the earth and the moon are attracting each other. So why have they not collided or why have they not touch each other :)

Is there any force which is keeping them away from each other ?

Thanks !
- MK

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Chris Peterson
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Re: Rearding Gravitational force

Post by Chris Peterson » Thu Jan 06, 2011 3:20 pm

mankavada wrote:There is a gravitational force between Earth and Moon. That means both, the earth and the moon are attracting each other. So why have they not collided or why have they not touch each other :)

Is there any force which is keeping them away from each other ?
There is no force keeping them away from each other. The reason they don't come together is because they are in orbit around their common center of mass (to a first approximation, you can say the Moon is in orbit around the Earth). What this means is that the bodies have a tangential velocity with respect to one another. If gravity were not present, the two would simply fly apart, along parallel lines in opposite directions. Gravity bends those parallel lines into ellipses, and the bodies now move around each other.
Chris

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neufer
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Regardingravitational farce

Post by neufer » Thu Jan 06, 2011 8:04 pm

Chris Peterson wrote:
mankavada wrote:
There is a gravitational force between Earth and Moon. That means both, the earth and the moon are attracting each other. So why have they not collided or why have they not touched each other :)

Is there any force which is keeping them away from each other ?
There is no force keeping them away from each other. The reason they don't come together is because they are in orbit around their common center of mass (to a first approximation, you can say the Moon is in orbit around the Earth). What this means is that the bodies have a tangential velocity with respect to one another. If gravity were not present, the two would simply fly apart, along parallel lines in opposite directions. Gravity bends those parallel lines into ellipses, and the bodies now move around each other.
Click to play embedded YouTube video.
Click to play embedded YouTube video.
http://en.wikipedia.org/wiki/Julius_Sumner_Miller wrote:
<<Julius Sumner Miller (May 17, 1909 – April 14, 1987) was an American physicist and television personality. He is best known for his work on children's television programs in North America and Australia.

Julius Sumner Miller was born in Billerica, Massachusetts the youngest of nine children. His Lithuanian mother spoke 12 languages, and his father was Latvian. Miller graduated with a Master in Physics from Boston University in 1933 but due to the Depression worked as a servant for the next two years during which time he married Alice Brown. A student of Albert Einstein, he was instantly recognizable by his casual hair and horn-rimmed spectacles.

In 1937 he obtained employment in the Physics Department of Dillard University, a private, black liberal arts college in New Orleans. He was to go on to the Physics Department of the Michigan College of Mining and Technology (1949–1951) and the Physics Department at El Camino College in Torrance, California (1952–1974), to maximum student enrollments due to his great popularity. From 1963 to 1986 he was the visiting lecturer for the Physics Department of the University of Sydney and from 1965 to 1985, the US Air Force Academy.

Miller began hosting his educational program, "Why Is It So?" in 1959 on KNXT Channel 2 in Los Angeles. From 1962 to 1964, Miller was Disney's "Professor Wonderful" on new introductions, filmed at Disneyland, to the syndicated reruns of The Mickey Mouse Club. During the same period, he appeared performing physics experiments, on Steve Allen's late night TV show in Hollywood; he was later an occasional guest in the 1970s on The Tonight Show Starring Johnny Carson. Miller is best known in Canada for his work as "The Professor" on the 1971 TV series The Hilarious House of Frightenstein.

Miller's first television appearance in Australia was on Bob Sanders People in 1963. In an improvised physics demonstration he attempted to drive a straw through a raw potato. A paper straw does not have the strength but if you pinch the end, the trapped air acts as a piston, easily piercing the potato. For the first time in his career he could not get it to work and loudly exclaimed "Australian straws ain't worth a damn". The next morning, Miller arrived at his Sydney University laboratory to find one million drinking straws on the floor with a telegram reading "You might find one of these fitting your requirements". He later stated "I sat amongst the straws with straws stuck in my hair and ears. But clearly I had made a mistake. I should have said: "Australian potatoes ain’t worth a damn," and I’d have cornered the potato market!"

Shortly after, he was offered a job presenting science for ABC Television. When asked how much money he wanted he replied he never asked, he listened to an offer then "multiplied it by a factor between two and ten". Due to budget constraints the offer was withdrawn but later an agreement was reached for Miller to host his own science based TV series. Why Is It So? (his eventual stock phrase), was broadcast from 1963 to 1986 and became an instant hit, the 1960s program became Demonstrations in Physics. He introduced each episode with the line: "How do you do, ladies and gentlemen, and boys and girls [sometimes adding "and teachers"]. I am Julius Sumner Miller, and physics is my business."

"My first TV series on demonstrations in physics - titled Why Is It So were now seen and heard over the land. The mail was massive. The academics were a special triumph for me. They charged me with being superficial and trivial. If I had done what they wanted my programs would be as dull as their classes! I knew my purpose well and clear: to show how Nature behaves without cluttering its beauty with abtruse mathematics. Why cloud the charm of a Chladni plate with a Bessel function?"

Miller's on-air popularity was due to an enthusiasm not normally associated with serious science. Shows would be liberally sprinkled with phrases such as "He who is not stirred by the beauty of it is already dead!" and he also liked to trick the audience. A common ploy would be to hold up an empty glass and ask guests to confirm it was empty....then chide them for not noticing it was full of air. Before each demonstration he would usually ask for a show of hands to indicate which of several results they expected. Often he would then add "hands up those who don’t care".

In 1966 questions from his show with an answer to the previous day’s question were published as "Millergrams" for The Australian newspaper. 112 of these questions were published as a book "Millergrams; Some Enchanting Questions for Enquiring Minds". Further books were published in 1967: "The Second Book of Millergrams: Some More Enchanting Questions for Enquiring Minds" and 1988: "Why is it So?: The Very Best Millergrams of Professor Julius Sumner Miller".
..........................................
Sample Millergram:

Q: A juggler comes to a foot-bridge of rather flimsy design. He has in hand four balls. The safe load is no more than the juggler himself and one ball. Can he get across the bridge by juggling the balls, always having at most one ball in the hand (and three in the air)?

A: No. A falling ball exerts a force on the hand greater than its own weight. Rather, a 'thrown' ball exerts greater force than a 'held' one. That is, the additional force equal and opposite to that imparted to a flung ball, in addition to the juggler's mass, would exceed the bridge's tolerance (the bridge can tolerate a juggler and held ball, but not the additional downward force associated with forcing a ball 'up').
..........................................
Miller died on April 14, 1987, of leukemia in San Jose, California. Professor Miller's wife, Alice Brown Miller, wanted to perpetuate the memory and achievements of her husband, and so conceived the idea of the Julius Sumner Miller Foundation, which was established in 1998. Miller willed his body to the University of Southern California's School of Dentistry.

In 1993 the Australian Science Foundation for Physics established the Julius Sumner Miller Fellowship in his memory. The fellowship is currently held by Karl Kruszelnicki, best known as "Doctor Karl" for his appearances on Australian radio and television as a science commentator and author.>>
Art Neuendorffer

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Chris Peterson
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Re: Regardingravitational farce

Post by Chris Peterson » Fri Jan 07, 2011 1:11 am

neufer wrote:(Some links referencing centrifugal force)
I fear your response may confuse the original question. Centrifugal force isn't even a real force, and it isn't responsible for balancing the force of gravity in an orbiting system.
Chris

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neufer
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Re: Regardingravitational farce

Post by neufer » Fri Jan 07, 2011 3:19 am

Chris Peterson wrote:
neufer wrote:(Some links referencing centrifugal force)
I fear your response may confuse the original question.

Centrifugal force isn't even a real force, and it isn't responsible for balancing the force of gravity in an orbiting system.
Julius Sumner Miller explicitly states a number of times that centrifugal force is not a real force.

Nevertheless, every physicist knows that concept of centrifugal force is a very useful one even if it is simply the consequence of a poor (i.e., rotating) frame of reference.

The concept of gravitational force is, likewise, a very useful one even if it too is simply the consequence of a poor (i.e., non free fall) frame of reference.

(In any event, I doubt that MK can become much more confused than he/she already is.)
Art Neuendorffer

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