Naked Science Forum
General Science => General Science => Topic started by: bigtim on 24/09/2006 11:28:49
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I recently and unwhitingly posted a comment on a few topics, stating that gravity is not a force. It was suggested to me that i start a new topic that might invite further discussion. Here we are then.
Below was my reply to people posting comments that contained the phrase "the force of gravity" or some similar expression:
"This is a common missconception. Gravity is not a force. The force is the product of mass and the strength of the gravitational filed, ie, the quotient of the ratio force/mass."
I have found a nicer way of describing gravity on Wikipedia:
"In physics, gravitation or gravity is the tendency of objects with mass to accelerate toward each other."
Any comments or other ways of describing gravity?
TW
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I think the problem is as much a question about what is a force as it is about what is gravity.
The problem is that the word 'force' is applied both to a measure and the supposed thing that induces that measure. That you can measure a force (i.e. weight yourself on a scale you measure your downward force) is one thing, but it is another thing to talk about a magnetic force, which is to describe the actual supposed source of the measurable effect.
Gravity can cause a downward force to appear, but equally one can use the word 'force' to describe the thing, namely gravity, that causes that measurable effect.
It is an unfortunate ambiguity in the English language, but it is not incorrect.
George
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quote:
Originally posted by another_someone
It is an unfortunate ambiguity in the English language, but it is not incorrect.
George
It is, is it not, dimensionally incorrect? Thus, does this imply that it is incorrect.
Big Tim
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Maybe gravity is not belonging to this universe at all
What you do speaks so loudly that I cannot hear what you say. (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.activity4life.com%2Fphoto%2Fsheepbouncing.gif+&hash=159acaa741febc5b65a3b1d93c7395d2)
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Gravity IS a force. its a force whats keeping us all on the earth u muppet lol its just that the way that the word FORCE is used that actually makes u right in saying its not a force.. but everybody knows it is really lol
an on explaining gravity thats simple, its a physical thing. We're living in the physical world.. and you cant see gravity but you do know its there, otherwise i could sit on the ceiling. Imagine a spring, and its connected to the edge of spice from the centre of the earth, but the spring is wide and all around the planet.. now when u jump u push on the spring, but the higher u get the spring pushes in the other direction out into space just to keep the same force on you. Thats how gravity works lol in a simple way. and we'll see gravity when scientists learn how 2.
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Ah I sense the certainty of youth [:D]
What you do speaks so loudly that I cannot hear what you say. (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.activity4life.com%2Fphoto%2Fsheepbouncing.gif+&hash=159acaa741febc5b65a3b1d93c7395d2)
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quote:
Originally posted by bigtim
quote:
Originally posted by another_someone
It is an unfortunate ambiguity in the English language, but it is not incorrect.
It is, is it not, dimensionally incorrect? Thus, does this imply that it is incorrect.
Actually not so.
What you said was that 'gravity is not a force' – the use of the indefinite article implies that you are not referring to a dimensioned entity at all, but a discrete entity.
If you had said that 'gravity is not force', then you may have been more correct.
The use of the indefinite article implied that you were not referring to a continuously measurable entity (something that could be measured in Newtons, or any fraction of a Newton), but that you were referring to a discrete entity (one discrete and identifiable force amongst many – e.g. magnetic force, Coriolis force, and gravitational force).
George
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quote:
Ah I sense the certainty of youth [:D]
I guess im not ranked in the youngest at this forum anymore. *sigh* oh well.
Earths gravity pulls you in the direction we call down. In space down does not exist, because the oreintation of gravity is not affecting us enough to notice it. Gravity is a pull from an object that is massive enough to have that effect. Any pull and/or push towards a direction is called a force. Any movement is an equation that shows the net force acting on an object. When you are falling, you go down because gravity is stronger than the force of wind resistance, which pushes up.
It would go against physics to not call gravity a force.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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quote:
Originally posted by ScouseLad
Gravity IS a force. its a force whats keeping us all on the earth u muppet lol its just that the way that the word FORCE is used that actually makes u right in saying its not a force.. but everybody knows it is really lol
an on explaining gravity thats simple, its a physical thing. We're living in the physical world.. and you cant see gravity but you do know its there, otherwise i could sit on the ceiling. Imagine a spring, and its connected to the edge of spice from the centre of the earth, but the spring is wide and all around the planet.. now when u jump u push on the spring, but the higher u get the spring pushes in the other direction out into space just to keep the same force on you. Thats how gravity works lol in a simple way. and we'll see gravity when scientists learn how 2.
quote:
Originally posted by science_guy
When you are falling, you go down because gravity is stronger than the force of wind resistance, which pushes up.
It would go against physics to not call gravity a force.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
To the 1st quote, I find it offensive that you use the word muppet, followed by LOL as if to counteract the insult. I started this as a topic to invite well mannered debate. Whilst I can take critisism, I feel it is inappropriate to use such insults. Howerver, back to the real question:
The second quote. I see what your saying, however the "downward" force is not gravity alone. The "downward" force is the product of your mass and the gravitaional field strenght, by the equation F=ma. If it were true that gravity were a force, then objects of differing masses would fall with the same force. they do not. They fall with the same speed because they are expiriencing the same acceleration due to gravity, however, say a mass of mkg(lets call it mass1) and a mass of 2mkg(mass2) were realease, the "downward force of mass1 would be halve that of mass 2. However, they are both falling under gravity, and so if gravity were a force, it would be uneven(I know gravity varies from place to place: that's a different topic of conversation)
I will say again, I would like to invite constructive criticism where appropriate.
TW
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I see what your saying, but your a little mixed up. Gravity is stronger the closer the objects are, and the more massive they are. If you dropped a bowling ball at the same time as a golf ball, they would land at different times EXCEPT for the fact that the bowling balls greater inertia (natural resistance by matter to movement), The difference is canncelled out to become an acceleration of 9.8 m/s/s.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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So what is the force in the "Air-force"? [:D]
May the force be with you all! [8D]
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quote:
Originally posted by science_guy
I see what your saying, but your a little mixed up. Gravity is stronger the closer the objects are, and the more massive they are. If you dropped a bowling ball at the same time as a golf ball, they would land at different times EXCEPT for the fact that the bowling balls greater inertia (natural resistance by matter to movement), The difference is canncelled out to become an acceleration of 9.8 m/s/s.
I don't mean to sound silly, but i really don't get what u r saying.
I get the first bit obviously, since F=(GMm)/(r^2)
Big Tim
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gravity is not a force scientifically speaking, but it is a force in the common usage of the word, just like a hurricane is a force or the police are a force. get it?
but i still agree with bigtim, in matters of actual scientific talk, which this site is 60% of the time, gravity is not a force.
"force" is startign to lose its meaning in my mind as i keep repeatign the word!
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quote:
Originally posted by gecko
gravity is not a force scientifically speaking, but it is a force in the common usage of the word, just like a hurricane is a force or the police are a force. get it?
but i still agree with bigtim, in matters of actual scientific talk, which this site is 60% of the time, gravity is not a force.
"force" is startign to lose its meaning in my mind as i keep repeatign the word!
OK, would you like to tell me what is a force?
I know what force (without the indefinite article) is, but that is not the same as a force, with the indefinite article preceding it.
Or are you saying that there is no such thing as a force?
George
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im not sure how "A" effects the word. really i have no idea. youre thinking way broader than my scope, which was just to comment on colloquial usage.
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quote:
Originally posted by gecko
im not sure how "A" effects the word. really i have no idea. youre thinking way broader than my scope, which was just to comment on colloquial usage.
If one asks 'what is a force acting upon a mass', then it implies that there are a number of different forces that are (or may) be acting upon a mass, and one is asked to specify one of them (e.g. gravity, coulomb force, magnetism, etc.).
If one asks 'what is the force acting upon a mass', one may be either suggesting that there can only possibly be one force, or that one wishes to know the composite value of the force (e.g. the total of the all the forces acting on the mass may amount to 5 newtons, and this could be used to calculate the acceleration of the mass).
George
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quote:
Originally posted by another_someone
... forces that are (or may) be acting upon a mass, and one is asked to specify one of them (e.g. gravity, coulomb force, magnetism, etc.)
...
George
They do, do they not, really mean the force due to the interaction of the mass with gravity, or the force due to a current carrying conductor being situated at a right-angle(or any angle between 0 and (pi/2)) to a magnetic field?
Big Tim
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I've siad for a long time that if IDers refuse to believe in evolution, i refuse to believe in gravity. so there is no matter to argue whether or not it is a force because it doesn't exist :)
Are YOUR mice nude? [;)]
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intelligent design fully explains the origin of life.
king of like the stork fully explains the origin of babies.
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Wait, you mean that the stork isn't the origin of babies?
but seriously, any explanation of life is about as likely as the second law of thermodynamics being violated. So the conclusion is that it cannot happen, or that it was intelligent design or evolution. The first option is ruled out, other wise I wouldn't be posting here, so that leaves either intelligent design, or evolution. There are numerous arguments for, and against both sides, for example, on the side of intelligent design, in order for life to be created, every single gene has to be placed in the right place in the right time, and has similar likelyhood of a stopwatch being formed from the raw materiels and being set at the right time by itself. But on the side of evolution, if the universe was created by God, then who created God? Putting that point aside, It is not likely that we will know for sure in the near future.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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this stopwatch thing has been exaplined to me several times and i still dont get the point.
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Gravity is a "field", as is electric charge and magnetism. A field is an area in which objects that can respond to the field can experience a force dependant on the property of the object and the property of the field.
All bodies with mass greate a gravitational field about them (in theory this field extends out to infinity) and when we are in the earth's gravitational field we experience a force towards the earth's centre of gravity that is proportional to our mass.
When we speak about the "force of gravity" we should really say the "force due the earth's gravitiaional field" but most people are lazy and contract it.
To my mind this contraction is not critical as long as we all understand what we are talking about and remember to express ourselves clearly where absolute precision is essential but this and many other linguistic somplifications and approximate models can cause problems when they are applied pedantically and beyond their limits.
For example I referred to the earth's centre of gravity (or mass) earlier in this reply. It is in fact unlikely that the gravitational attraction at any point on the earth's surface is exactly towards this mathematical point (which does exist at a location from instant to instant) at any time because the varing topology of the location and the varying density of rocks will deflect and modify the local gravitiational field. This is a fact that is used for prospecting for minerals. the exact variations in the magnitude abd direction of the earth's local gravitiational field can give useful information on what lies below the surface.
Learn, create, test and tell
evolution rules in all things
God says so!
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I guess the first question is "What is a force?" My understanding is that it is defined by this statement "A body in motion tends to remain in motion unless disturbed by an external force." So we can tell if there is a force by whether a body is disturbed from its "natural motion". I once read the following interpretation of Newtons law: "A body in motion tends to remain in motion unless it doesn't and then we call it an external force." The problem is what does remaining in motion mean? According to Newton it was constant velocity measured against a rectilinear grid that is "not accelerating" - roughly not accelerating "relative to the fixed stars" which I assume means the center of mass of the universe but really think it was undefined. By this definition there is a force of gravity as can be seen by throwing a ball slowly into the air and watching it not keep going up, but rather come back down. My understanding is that Einstein latter changed the meaning of "remaining in motion" to mean traveling on a "geodesic" of a curved spacetime. The ball I throw upwards travels on this geodesic and so it "remains in motion" even as it falls. Therefore there is no "force" of gravity. It is just traveling on the straightest line it can in spacetime. The good thing is that it makes it easier to see why when you hold a ball in your hand you have to apply a force! You are making it deviate from its geodesic motion so you have to apply a force! However even in Einsteins world gravity can rip you appart because if the spacetime is curved enough the "natural motion" of your feet will be different from the "natural motion" of your head and so you get torn apart even if there is no force! I think these are called "tidal" "gravitational forces"... which further confuses the issue. P.S. I am not a scientist so be careful listening to me.
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I guess the first question is "What is a force?" My understanding is that it is defined by this statement "A body in motion tends to remain in motion unless disturbed by an external force." So we can tell if there is a force by whether a body is disturbed from its "natural motion". I once read the following interpretation of Newtons law: "A body in motion tends to remain in motion unless it doesn't and then we call it an external force." The problem is what does remaining in motion mean? According to Newton it was constant velocity measured against a rectilinear grid that is "not accelerating" - roughly not accelerating "relative to the fixed stars" which I assume means the center of mass of the universe but really think it was undefined. By this definition there is a force of gravity as can be seen by throwing a ball slowly into the air and watching it not keep going up, but rather come back down. My understanding is that Einstein latter changed the meaning of "remaining in motion" to mean traveling on a "geodesic" of a curved spacetime. The ball I throw upwards travels on this geodesic and so it "remains in motion" even as it falls. Therefore there is no "force" of gravity. It is just traveling on the straightest line it can in spacetime. The good thing is that it makes it easier to see why when you hold a ball in your hand you have to apply a force! You are making it deviate from its geodesic motion so you have to apply a force! However even in Einsteins world gravity can rip you appart because if the spacetime is curved enough the "natural motion" of your feet will be different from the "natural motion" of your head and so you get torn apart even if there is no force! I think these are called "tidal" "gravitational forces"... which further confuses the issue. P.S. I am not a scientist so be careful listening to me.
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One of Big Tim's corrections was aimed at me in relation to something I'd said about woodpeckers hammering into trees.
I'm grateful to Tim for highlighting this sloppy phraseology, which I will endeavour to avoid in future. You're quite right Tim, it is a silly thing to say.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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quote:
Originally posted by chris
One of Big Tim's corrections was aimed at me in relation to something I'd said about woodpeckers hammering into trees.
I'm grateful to Tim for highlighting this sloppy phraseology, which I will endeavour to avoid in future. You're quite right Tim, it is a silly thing to say.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
hehe, sorry Chris.
quote:
"When we speak about the "force of gravity" we should really say the "force due the earth's gravitiaional field" but most people are lazy and contract it." (soul surfer)
I am willing to accept that, as soul surfer points out, that it lazy shortening and will be impossible to iradicate. I still do maintain that gravity is not a force, though will not be so snobby as to criticise people for alikening gravity to a force.
Big Tim
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quote:
Originally posted by bigtim
I am willing to accept that, as soul surfer points out, that it lazy shortening and will be impossible to iradicate. Big Tim
Sorry Tim, but I can't resist giving you a dose of your own medicine, but you've spelled ERADICATE incorrectly.
Everyone, I'm starting a new discussion topic in which we scrutinise all Tim's posts for spelling mistakes... [;)]
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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quote:
Originally posted by chris
quote:
Originally posted by bigtim
I am willing to accept that, as soul surfer points out, that it lazy shortening and will be impossible to iradicate. Big Tim
Sorry Tim, but I can't resist giving you a dose of your own medicine, but you've spelled ERADICATE incorrectly.
Everyone, I'm starting a new discussion topic in which we scrutinise all Tim's posts for spelling mistakes... [;)]
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
Hmmm yes, it appears as though you're right. Indeed, when trying to write ERADICATE I did wonder whether I had spelt it correctly. To avoid further embarrassment, I have put this through a spellchecking thing so I can use big words/phrases, such as “chiropody” and “Public Expenditure Review”, if I so wish.
I never was good at English. Oh well…never mind…[:(]
Tim
Big Tim
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Tch. Careless. ;)
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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As I understand it rate of relative motion can only be changed by the application of a force thus f=ma (force = mass times acceleration)
so when a mass accelerates it is due to a force acting upon it.
In the case of objects falling to earth that force is due to gravity
thus the correct term should be "Acceleration due to gravity" rather than
force of gravity - or am I talking bollocks again?
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When the force is also proportional to the mass (i.e. M1 M 2G/rsquared) then the acceleration is all that counts.
m/secondsquared is the equivalent to newtons /kg .
Not "bollocks", I think.