Science stories of the week

exchemist said:
It is because there is no way to neutralise this interaction, so far as we know.

In electromagnetism you have +ve and -ve charges, which when they are in balance cancel each other out so that no net force remains. For instance if you bring an -(-ve) electron close to a (+ve) proton it gets "smeared out" all round the proton and cancels its +ve charge, giving you a hydrogen atom which is electrically neutral and thus exerts little* electromagnetic force on anything at longer range. Something similar happens when subatomic particles are brought together under the influence of the nuclear forces. So all these interactions get neutralised by bringing fundamental particles of matter together. So in practice you never get large collections of "bare", unbalanced, fundamental particles of matter.

But with gravitation, there is no neutralisation when particles of matter are brought together. On the contrary, the gravitational effect is made larger when particles clump together. You don't have +ve and -ve gravitational charges - or not as far as we know. So there is no process to limit the effect of gravitation, in the way that there is for all the other interactions.



* Though another atom brought close to it will feel an electromagnetic effect, potentially causing the atom to form a chemical bond with it. This further lessens the electromagnetic effect, so that there is almost none at all between a a pair of hydrogen molecules. Though there is still actually a tiny bit, which can be imagined as due to a flickering motion of the electrons about the protons, which causes tiny random imbalances of charge. These produce a tiny attraction between molecules, known as "dispersion" or "London" forces. This intermolecular attraction is the reason why gases condense into liquids and then solids at low enough temperatures.. Apologies for the digression into chemistry.:wink:
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No apologies needed. :wink:

Is it safe to say that gravity seems stronger than it's given credit for, because it's always attractive?

I guess what stumps me a bit is suppose you're laying down under an apple tree, and apples begin falling from the tree, landing on your head. Wouldn't it seem that gravity (at that very moment) isn't weak at all? We tend to take gravity for granted in every day life, because we don't ''feel it.'' I guess what I'm asking is how can gravity be such a fundamental force, yet weak?
 
wegs said:
No apologies needed. :wink:

Is it safe to say that gravity seems stronger than it's given credit for, because it's always attractive?

I guess what stumps me a bit is suppose you're laying down under an apple tree, and apples begin falling from the tree, landing on your head. Wouldn't it seem that gravity (at that very moment) isn't weak at all? We tend to take gravity for granted in every day life, because we don't ''feel it.'' I guess what I'm asking is how can gravity be such a fundamental force, yet weak?
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A fly can walk across the ceiling without being pulled off.

The Earth is huge and is pulling your arm down but it doesn't take much effort/energy on your part to simply bend your elbow and counteract all that gravity.
 
wegs said:
No apologies needed. :wink:

Is it safe to say that gravity seems stronger than it's given credit for, because it's always attractive?

I guess what stumps me a bit is suppose you're laying down under an apple tree, and apples begin falling from the tree, landing on your head. Wouldn't it seem that gravity (at that very moment) isn't weak at all? We tend to take gravity for granted in every day life, because we don't ''feel it.'' I guess what I'm asking is how can gravity be such a fundamental force, yet weak?
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Being fundamental isn't a question of strength, it's a question of whether something can be explained in terms of something else or not. And gravitation can't. It just is what it is, so far as we know at the moment. That's what we mean by fundamental.
 
One way to compare the relative strengths of forces is to see how different forces act on the same objects.

Consider, for example, the electric force between two electrons, separated by 1 metre. The force is $2.3\times 10^{-28}$ Newton, which is a small force.

But compare the force of gravity between the two electrons at the same separation. That force is $5.5 \times 10^{-71}$ Newton.

In other words, for this example, the electric force is about $10^{42}$ times strong than the gravitational force.

That's 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times stronger.
 
James R said:
One way to compare the relative strengths of forces is to see how different forces act on the same objects.

Consider, for example, the electric force between two electrons, separated by 1 metre. The force is $2.3\times 10^{-28}$ Newton, which is a small force.

But compare the force of gravity between the two electrons at the same separation. That force is $5.5 \times 10^{-71}$ Newton.

In other words, for this example, the electric force is about $10^{42}$ times strong than the gravitational force.

That's 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times stronger.
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Yeah, but gravity says to electro -magnetism "Is that all you got? See you around"
:biggrin:
 
James R said:
One way to compare the relative strengths of forces is to see how different forces act on the same objects.

Consider, for example, the electric force between two electrons, separated by 1 metre. The force is $2.3\times 10^{-28}$ Newton, which is a small force.

But compare the force of gravity between the two electrons at the same separation. That force is $5.5 \times 10^{-71}$ Newton.

In other words, for this example, the electric force is about $10^{42}$ times strong than the gravitational force.

That's 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times stronger.
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Okay, when you compare the math equations, it's the weakest, but in terms of importance (because of its incredible range/reach), it should be considered the strongest, no? It's the most strongly present force in our lives, every single day. (Even though we can't detect it.)
And all things considered, gravity is inevitable.
 
wegs said:
Okay, when you compare the math equations, it's the weakest, but in terms of importance (because of its incredible range/reach), it should be considered the strongest, no? It's the most strongly present force in our lives, every single day. (Even though we can't detect it.)
And all things considered, gravity is inevitable.
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Actually the reach of the electromagnetic force is the same as that of gravitation. Both obey inverse square laws, i.e. if you double the separation between objects, the force falls to 1/2², i.e to 1/4 of what it was before.

The reason for the effect of gravity at vast distance is that, unlike the electrostatic force, it does not get neutralised when objects attracted because of it come together. So it becomes cumulative.

If you could somehow get a mass of electrons together, on their own, that had the same mass as the earth, the electrostatic force they would exert on charged objects in space would be immense, far greater than gravity. But you can't do that, because such a collection of electrons would firstly fly apart under their colossal mutual repulsion, and even if that could be prevented, it would strip protons from everywhere around in space until it was largely neutralised by them. The same sort of thing applies to the other fundamental interactions too.

But not to gravity, which is why it alone can accumulate large amounts of matter together and thereby magnify its "weak" influence until it outstrips everything else.
 
exchemist said:
But not to gravity, which is why it alone can accumulate large amounts of matter together and thereby magnify its "weak" influence until it outstrips everything else.
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exchemist said:
Both obey inverse square laws
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I get that

But somewhere out there the inverse square law breaks down to a Planck Length

Soooo do you speculate there is a space (I'm thinking middleish between galaxies) where there is no Gravity

:) Asking for a friend :)

:)
 
Michael 345 said:
I get that

But somewhere out there the inverse square law breaks down to a Planck Length

Soooo do you speculate there is a space (I'm thinking middleish between galaxies) where there is no Gravity

:) Asking for a friend :)

:)
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Planck length remains a speculative theoretical concept, so far as I am aware, with no observable effects.
 
exchemist said:
Actually the reach of the electromagnetic force is the same as that of gravitation. Both obey inverse square laws, i.e. if you double the separation between objects, the force falls to 1/2², i.e to 1/4 of what it was before.

The reason for the effect of gravity at vast distance is that, unlike the electrostatic force, it does not get neutralised when objects attracted because of it come together. So it becomes cumulative.

If you could somehow get a mass of electrons together, on their own, that had the same mass as the earth, the electrostatic force they would exert on charged objects in space would be immense, far greater than gravity. But you can't do that, because such a collection of electrons would firstly fly apart under their colossal mutual repulsion, and even if that could be prevented, it would strip protons from everywhere around in space until it was largely neutralised by them. The same sort of thing applies to the other fundamental interactions too.

But not to gravity, which is why it alone can accumulate large amounts of matter together and thereby magnify its "weak" influence until it outstrips everything else.
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Thank you for explaining further. I guess what I'm getting at is that it just seems comparing gravity to the other forces, is like comparing apples to watermelons. I'm now understanding why gravity is considered the weakest of the forces, but the forces themselves don't seem entirely comparable?
 
wegs said:
Thank you for explaining further. I guess what I'm getting at is that it just seems comparing gravity to the other forces, is like comparing apples to watermelons. I'm now understanding why gravity is considered the weakest of the forces, but the forces themselves don't seem entirely comparable?
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They don't need to be comparable. They need to be forces and they need to be describable and when two are called the strong force and the weak force this brings forth the comment that gravity is the weakest especially in that it has a small role to play in particle physics where the standard model of the 4 fundamental forces comes from in the first place.
 
wegs said:
For this week...

http://www.insidescience.org/news/feeding-seaweed-cattle-could-help-curb-climate-change
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feeding-seaweed-cattle-could-help-curb-climate-change

im not sure seaweed can properly digest cattle

it would be more beneficial to feed humans seaweed & allow cattle to die out as a domesticated stock animal

if we look at the carbon transfer
you still need to grow the seaweed that will be eaten by th cattle
what happens to the paddocks of grass where the cattle live ?
over nitrating the cattle which then poops into the ground, then rns off
you would still need to have capture process i to re-capture the excess nitrates

the beef industry need to be reduced in size
did we see the beef industry out campaigning to block driver less taxis ?
nope
what about bio-fuel ?
did they campaign against that ? nope

beef farming has seen its day
meat eating is old world
birds no problem
cattle = huge problem
like driving old cars that are wasteful on fuel and produce lots of pollution
red meat farming is too high in methane & excess resources to produce it

it would be fine if they were open grazing o massively huge pastures hundreds and thousands of square kilometers wide
but hats not how money works
and thats not how greed drives human economics

its just a fact of human evolution and the terrible pollution and climate change human civilization has cast upon the world

cattle farmers should switch to mushrooms and turkeys & small beef production organic etc
 
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wegs said:
For this week...

http://www.insidescience.org/news/feeding-seaweed-cattle-could-help-curb-climate-change
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This is very interesting. I see from the article that CHBr₃ does however have potential to be an ozone-depleting compound, so they will need to assure themselves about that before implementing this commercially. However since it seems to be short-lived in the atmosphere, it may not be an issue. The great thing about this is that it makes the animals convert food more efficiently as well, so there is a commercial incentive for the farmer to use it, apart from its beneficial effect on methane emissions.

One just hopes there is enough red seaweed to go round.
 
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