Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: imd321 on 26/06/2009 14:12:59

Title: How big before an object has a demonstrable gravitational effect?
Post by: imd321 on 26/06/2009 14:12:59

How big does something have to be before it would have a noticeable gravitational impact.  It would obviously be something bigger than Everest since people don't seem to feel any sensation of being pulled towards it.

Title: Re: How big before an object has a demonstrable gravitational effect?
Post by: LeeE on 26/06/2009 14:55:03

I recall reading somewhere that in large tournaments, with correspondingly large local audiences, the path of a snooker ball cannot be accurately predicted after six or seven (I think) rebounds off of the cushions because of the gravitational influence of the surrounding audience.

Dunno if it's true or not; I've never been good enough at snooker to tell, or play with a large audience.

Title: Re: How big before an object has a demonstrable gravitational effect?
Post by: lyner on 26/06/2009 18:27:44

On a slightly different tack- it's been said that the gravitational influence of the planets on a baby at birth (i.e. astrological influences) is no greater than the effect of the midwife who's standing next to the bed.

Title: How big before an object has a demonstrable gravitational effect?
Post by: Madidus_Scientia on 27/06/2009 07:59:49

And i've heard that a 747 flying above you has more gravitational effects on you than the planets even if they were all perfectly aligned.

Title: How big before an object has a demonstrable gravitational effect?
Post by: syhprum on 27/06/2009 10:20:56

I think there is about 1% truth in astrology, Jupiter's 11 year orbit could well affect the Sun spot cycle that in turn affects our lives.

Title: How big before an object has a demonstrable gravitational effect?
Post by: RD on 27/06/2009 10:44:40

Quote from: imd321 on 26/06/2009 14:12:59

How big does something have to be before it would have a noticeable gravitational impact. 

Depends on the sensitivity of the apparatus used to measure it ...

Quote

Michell conceived, sometime before 1783, the experiment now known as the Cavendish experiment. It was the first to measure the force of gravity between masses in the laboratory* and produced the first accurate values for the mass of the Earth and the gravitational constant. He invented and built, independently of co-inventor Charles Augustin de Coulomb, a torsion balance for the experiment but didn’t live to put it to use. His apparatus passed to Henry Cavendish, who performed the experiment in 1798.

http://en.wikipedia.org/wiki/John_Michell

[* So smaller than Mt Everest]

Title: How big before an object has a demonstrable gravitational effect?
Post by: lyner on 27/06/2009 16:36:42

The spacing of the orbital stations of geosynchronous satellites has to be kept large enough to avoid too much mutual gravitational effect. Even they have masses of only hundreds of kg, they have to be spaced thousands of km apart or they would start to tumble (orbit) around each other and consume too much station-keeping fuel.
Asteroids and the debris of Saturn's rings all are affected by mutual gravity.