How does gravity work?
Discussion
RTB said:
TwigtheWonderkid said:
I get where the op is coming from. It seems odd that gravity is strong enough for the sun to hold Pluto in an orbit, yet at the same time weak enough for me to be able to pick up my mug of tea.
What if your mug of tea was the size of pluto though? Boring_Chris said:
julian64 said:
I suggest less pies or pick a smaller hill.
I want this in an equation.where Ag is the acceleration due to gravity
G is the universal gravitational constant
M is the mass of the body
r is the radius of the body For comparison, Ag = 9.8 m/s^2 for the surface of the Earth. Otherwise known as 1g
ie. bigger radius (the further you are from the earths core) the smaller the acceleration due to gravity
Reference https://www.physicsforums.com/threads/more-density...
Pies are not factored in as physics geeks struggle to explain them
Is this not a question of thermodynamics, rather than gravity?
I mean, gravity will play a role but the bigger factors will be the weight of the bloke, the bike, his Team GB jacket etc then distance and incline. Then air density, available oxygen etc.
Everest is only 5 miles or so high. You're not exactly operating in a different dimension of time and space when climbing even the highest of mountains.
Edit. "earth were reduced to the size of a billiard ball, its surface would be smoother"
Would this not be due to it's large mass (but small size) compacting matter on a subatomic level? If you've squashed Earth to the size of a billiard ball, you're into gravity well territory. Like a friendly version of a black hole?
I mean, gravity will play a role but the bigger factors will be the weight of the bloke, the bike, his Team GB jacket etc then distance and incline. Then air density, available oxygen etc.
Everest is only 5 miles or so high. You're not exactly operating in a different dimension of time and space when climbing even the highest of mountains.
Edit. "earth were reduced to the size of a billiard ball, its surface would be smoother"
Would this not be due to it's large mass (but small size) compacting matter on a subatomic level? If you've squashed Earth to the size of a billiard ball, you're into gravity well territory. Like a friendly version of a black hole?
Edited by Boring_Chris on Tuesday 21st February 14:28
blueg33 said:
Boring_Chris said:
julian64 said:
I suggest less pies or pick a smaller hill.
I want this in an equation.where Ag is the acceleration due to gravity
G is the universal gravitational constant
M is the mass of the body
r is the radius of the body For comparison, Ag = 9.8 m/s^2 for the surface of the Earth. Otherwise known as 1g
ie. bigger radius (the further you are from the earths core) the smaller the acceleration due to gravity
Reference https://www.physicsforums.com/threads/more-density...
Pies are not factored in as physics geeks struggle to explain them
Mysteries of the universe... black holes, dark matter, and pies!
Boring_Chris said:
Went on a little science binge when looking up at the Moon and getting all confused last year... going in absolutely clueless, this stuff just knocked me for six!
From what I understood, gravity is a consequence of mass warping both time and space. 'Gravity' is a 'weak force' but is absolutely unstoppable... The greater the mass, the greater the pull. I seem to remember reading that even if you were impervious to heat, should you ever visit, you'd be spaghettified - or at least partially torn to bits - by the gravitational pull of the sun... ?
Spaghettification would be caused by a black hole. The sun's surface gravity is 'only' 28g, so you'd probably be crushed by your own body weight, but the tidal forces are the least of your worries.From what I understood, gravity is a consequence of mass warping both time and space. 'Gravity' is a 'weak force' but is absolutely unstoppable... The greater the mass, the greater the pull. I seem to remember reading that even if you were impervious to heat, should you ever visit, you'd be spaghettified - or at least partially torn to bits - by the gravitational pull of the sun... ?
Halmyre said:
Boring_Chris said:
Went on a little science binge when looking up at the Moon and getting all confused last year... going in absolutely clueless, this stuff just knocked me for six!
From what I understood, gravity is a consequence of mass warping both time and space. 'Gravity' is a 'weak force' but is absolutely unstoppable... The greater the mass, the greater the pull. I seem to remember reading that even if you were impervious to heat, should you ever visit, you'd be spaghettified - or at least partially torn to bits - by the gravitational pull of the sun... ?
Spaghettification would be caused by a black hole. The sun's surface gravity is 'only' 28g, so you'd probably be crushed by your own body weight, but the tidal forces are the least of your worries.From what I understood, gravity is a consequence of mass warping both time and space. 'Gravity' is a 'weak force' but is absolutely unstoppable... The greater the mass, the greater the pull. I seem to remember reading that even if you were impervious to heat, should you ever visit, you'd be spaghettified - or at least partially torn to bits - by the gravitational pull of the sun... ?
Boring_Chris said:
Edit. "earth were reduced to the size of a billiard ball, its surface would be smoother"
Would this not be due to it's large mass (but small size) compacting matter on a subatomic level? If you've squashed Earth to the size of a billiard ball, you're into gravity well territory. Like a friendly version of a black hole?
No, it's because the surface irregularities on a billiard ball are supposedly a larger percentage of its radius than the mountains of the earth. However, it seems as if it's a myth anyway.Would this not be due to it's large mass (but small size) compacting matter on a subatomic level? If you've squashed Earth to the size of a billiard ball, you're into gravity well territory. Like a friendly version of a black hole?
Edited by Boring_Chris on Tuesday 21st February 14:28
To answer the OP directly, the difference with going up a hill is simply that you're increasing your potential energy in doing so. If you imagine that gravity is a giant spring applying a force pulling you towards the centre of the earth (and the earth towards you, of course), then going up a hill is like stretching that spring out to a further distance, whereas riding on the flat keeps the spring the same length. Because when you're riding on the flat the tyres react against the ground stopping you falling towards the centre of the earth, you don't have to work hard to stay at the same distance from the centre of the earth. The only way gravity affects you when riding on the flat is that your weight causes the tyres to squash into a contact patch with the ground (which is proportional in area to your weight and the air pressure in your tyres, but curiously not proportional to the width of the tyre..), and that contact patch at the base of the tyre requires the tyre to squash into and out of shape constantly as it rotates, which takes energy. Note that the energy required to accelerate you is a factor of your inertial mass, which is different to your gravitational mass...
RobM77 said:
... your inertial mass, which is different to your gravitational mass.
Perhaps a little more precisely, they are the same thing but classical physics couldn't explain why. There's nothing in Newton's laws of motion and gravitation that explains why the "m" in the two models has to be the same thing. It was just observation that suggested it was, e.g. Galileo fly tipping from the tower in Pisa.
ATG said:
RobM77 said:
... your inertial mass, which is different to your gravitational mass.
Perhaps a little more precisely, they are the same thing but classical physics couldn't explain why. There's nothing in Newton's laws of motion and gravitation that explains why the "m" in the two models has to be the same thing. It was just observation that suggested it was, e.g. Galileo fly tipping from the tower in Pisa.
I was trying to keep things as simple as possible, but to be honest I slipped up there. I sort of inferred that they measured differently, whereas what I was trying to say was simply that inertia had nothing to do with gravity.To answer the OP, we don't know.
I've heard several explanations.
One was that everything is expanding, gravity is simply the acceleration caused by this expansion.
Another was that the zero point energy field flows towards massive objects. This creates a drag on every atom in your body. You feel that as gravity.
Mike McCulloch has some very interesting things to say about gravity on his blog "Physics from the edge". I think he's right. Take a look. If nothing else he'll make you wonder why we devote so much effort into supporting modern physics with invisible stuff that can't be detected such as Dark Matter and Dark Energy and Dark flow. He's right to point out that it all looks like increasingly desperate attempts to invent magic material with just the right properties to make everything agree with their existing theories.
I've heard several explanations.
One was that everything is expanding, gravity is simply the acceleration caused by this expansion.
Another was that the zero point energy field flows towards massive objects. This creates a drag on every atom in your body. You feel that as gravity.
Mike McCulloch has some very interesting things to say about gravity on his blog "Physics from the edge". I think he's right. Take a look. If nothing else he'll make you wonder why we devote so much effort into supporting modern physics with invisible stuff that can't be detected such as Dark Matter and Dark Energy and Dark flow. He's right to point out that it all looks like increasingly desperate attempts to invent magic material with just the right properties to make everything agree with their existing theories.
cymtriks said:
To answer the OP, we don't know.
I've heard several explanations.
One was that everything is expanding, gravity is simply the acceleration caused by this expansion.
Another was that the zero point energy field flows towards massive objects. This creates a drag on every atom in your body. You feel that as gravity.
Mike McCulloch has some very interesting things to say about gravity on his blog "Physics from the edge". I think he's right. Take a look. If nothing else he'll make you wonder why we devote so much effort into supporting modern physics with invisible stuff that can't be detected such as Dark Matter and Dark Energy and Dark flow. He's right to point out that it all looks like increasingly desperate attempts to invent magic material with just the right properties to make everything agree with their existing theories.
If we're getting into how gravity actually works (rather than my interpretation of the question, which was simply a Newtonian explanation of potential energy), before we deal with how it actually works, as you've described (and as you say, the correct answer is that we don't know), we need to take a step back and establish whether the OP is familiar with the Newtonian basics, such as I alluded to. Then we need to move on to ask if he's familiar with General Relativity, which as I'm sure many of us know, simply states that massive objects distort space-time, and as time (the 4th dimension in 'space-time') ticks by, that distorted space-time simply brings things closer together, much as two people walking parallel and north from the equator end up together because of the curved surface of the earth.I've heard several explanations.
One was that everything is expanding, gravity is simply the acceleration caused by this expansion.
Another was that the zero point energy field flows towards massive objects. This creates a drag on every atom in your body. You feel that as gravity.
Mike McCulloch has some very interesting things to say about gravity on his blog "Physics from the edge". I think he's right. Take a look. If nothing else he'll make you wonder why we devote so much effort into supporting modern physics with invisible stuff that can't be detected such as Dark Matter and Dark Energy and Dark flow. He's right to point out that it all looks like increasingly desperate attempts to invent magic material with just the right properties to make everything agree with their existing theories.
Our bodies are amazing things and perfectly adapted to living with 1g, so it feels easy.....but there is a reason our leg muscles are as big as they are.....as they are constantly fighting that 1g to even stay upright, you just don't notice. Try hanging from a bar and see how your arm & hand muscles stack up :-). Not so easy now ?
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