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Gravity: What Is It?

I find that clicking on the links gives me a couple of paragraphs of text then a message saying I need to subscribe if I want to continue reading the item.

I am tempted to subscribe for the on-line version. I gave up the paper version as it was belt tightening time.
 
I find that clicking on the links gives me a couple of paragraphs of text then a message saying I need to subscribe if I want to continue reading the item.
I don't, as in:

1549924688291940.jpg


Maybe something to do with, 'cookies' from a previous visit to the web site?
 
Continued.... if you type in that URL, it does indeed take you to the 'subscribe' invitation... however, if you search for, 'new scientist gravity', the article is duly highlighted and that link evidently bypasses the subscription requirement.
 
I was pondering something in the early hours again;

If there was a sphere, say the size of a small town, and I were to walk from the 'North' to the 'South pole', I would know that I was upside down- the blood would be rushing to my head and I would probably feel a bit queezy- unlike when on a huge planet such as earth and there is no discernible effect.

At what size then, would the sphere have to be before it became like the earth, ie no effect was noticed?

And does the Sorites paradox then come into play as well?
 
I was pondering something in the early hours again;

If there was a sphere, say the size of a small town, and I were to walk from the 'North' to the 'South pole', I would know that I was upside down- the blood would be rushing to my head and I would probably feel a bit queezy- unlike when on a huge planet such as earth and there is no discernible effect.

At what size then, would the sphere have to be before it became like the earth, ie no effect was noticed?

And does the Sorites paradox then come into play as well?
You would notice because the Earth is very much more massive than the sphere you are walking on, and the Earth' gravity is what you will be feeling. If your sphere was outside of the immediate influence of Earth, it would have a very low, but equal, gravity all around the sphere, and you would not notice the difference. unless your little sphere was massively dense like a neutron star, in which case it would overcome the Earth's gravity (the Earth would fall into the sphere!)
 
Just to add some more variables, most of which I don't understand either :)

There is a certain size with natural objects when the accumulation of matter produces a sphere rather than an irregular lump. I think it is part of the definition of dwarf planets.

Mass plays a part as @SimonBurchell said.

With enough mass, tidal forces come into play as well.

Wasn't sure @Floyd1 whether you were thinking of a sphere floating close to the Earth, or one in space?

One thing I am pretty sure of though is that you won't be standing on the surface of a neutron star for long enough to worry about it as the gravitational pull is massive.
 
When they send space craft to sample asteroids they they seem to be able to land
and orbit them so even relatively small objects must have gravity,

Gravity is a myth the Earth suckes.
 
Just to add some more variables, most of which I don't understand either :)

There is a certain size with natural objects when the accumulation of matter produces a sphere rather than an irregular lump. I think it is part of the definition of dwarf planets.

Mass plays a part as @SimonBurchell said.

With enough mass, tidal forces come into play as well.

Wasn't sure @Floyd1 whether you were thinking of a sphere floating close to the Earth, or one in space?

One thing I am pretty sure of though is that you won't be standing on the surface of a neutron star for long enough to worry about it as the gravitational pull is massive.
I was thinking of the sphere as a stand alone 'planet' if you like, floating in space. I hadn't considered its proximity to earth or anything else.
 
I was thinking of the sphere as a stand alone 'planet' if you like, floating in space. I hadn't considered its proximity to earth or anything else.
Then wherever you are standing "down" would be where your feet are. Gravity would act to pull you toward the centre of the sphere. (Actually your gravity would pull on the sphere as well, so it would pull you to the centre of mass of the two of you)

https://en.wikipedia.org/wiki/Barycenter_(astronomy)

Of course if the sphere is small enough you may be able to jump off of it - this site is a bit of fun and shows how high you can jump on on different planets, comets, etc. https://cosmos-book.github.io/high-jump/index.html

Reminds me of Fritz Zwicky's insult where he called some of his colleagues "Spherical bastards," because "They were bastards whichever way you looked at them."
 
Landing on an asteroid is much trickier than expected. The Philae spaceccraft was supposed to land on asteroid Churyumov–Gerasimenko, which has about 1/10,000 the gravity of Earth. The lander was supplied with a cold-gas thruster and harpoons designed to stick it to the surface, but neither of these worked correctly.

Instead the lander bounced at 15:34, 16:20 and 17:35,reaching 1km high during the bounce, at which time it finally landed half-upside-down in a crevice (like a drunken bloke stuck behind the sofa trying to switch the Christmas tree lights on).
480px-Philae_close-up_labelled.jpg
 
S'funny. But yes, astrodynamics are super hard to nail. I remember Gene Cernan's description of nearly dying on a Gemini mission because he couldn't anchor anywhere on his module on a spacewalk in zeroG. It was a real bad trip, He was a bit pissed when Aldrin got the slippers in a later Gemini mission. Said he had it easy. Navy guys, eh.
 
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