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Is gravity a pull?


Capiert
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If yes please prove it.

All I observe is,

gravitational acceleration "g is only an acceleration".

That does NOT imply (only) "pull" to me.

I get hints, it's (=the acceleration is) the opposite (direction), instead.

Please clarify.

 

Wiki's "Centrifugal force", says,

"fictitious forces, like gravity, pulls.."

 

If they are NOT real forces,

then are they in the right direction, at all?

E.g. Gravity is NOT a force?

 

Wiki gives no reference to [1]:

"The centrifugal force

is an outward force (which I recognize as, only "acceleration", of mass)

apparent in a rotating reference frame;

it does NOT exist
when measurements are made
in an inertial frame of reference[1]."

I find the (Wiki) statements admirable, & courageous (against ridicule).
But I don't know what the status quo is. (..But can (sure) guess.)

 

 

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According to Newton's law of universal gravitation, all objects with a certain mass exert some attracting force towards each other.

 

That fact has nothing to do with eventual other forces to which an object is exerted (e.g. centrifugal force by rotational movement).

 

The force by which 2 objects attract each other is expressed by the following formula

 

[math]F=G\cdot\frac{m_1\cdot m_2}{r^2}[/math]

 

F being the attracting force, G being the gravitational constant, m1 being the mass of one object, m2 being the mass of the other object and r being the distance between the centres of mass of both objects.

 

So surely, earth and its gravitation are attracting you.

 

To come to the gravitational acceleration g we all know:

 

[math]F=m\cdot a[/math]

 

F being the resultant force exerted on an object with mass m subjected to an acceleration a.

 

Let's combine this with the earlier formula. Let's say you have a mass m2 and earth has mass m1.

 

If we want to know the acceleration a we are subjected to as per result of the gravitational force, given that we are not subjected to any other force:

 

[math]F = m_2 \cdot a[/math]

 

[math]\Leftrightarrow \frac{F}{m_2}=a=G\cdot\frac{m_1}{r^2}[/math]

 

[math]\Leftrightarrow \frac{F}{m_2}\approx 6.67408\cdot 10^{-11}\text{ }\frac{\text{m}^3}{\text{kg}\cdot\text{s}^{-2}}\cdot \frac{5.972\cdot 10^{24} \text{ kg}}{6,371,000^2\text{ m}^2}[/math]

 

[math]\Leftrightarrow \frac{F}{m_2}\approx 9.82\text{ }\frac{\text{m}}{\text{s}^2}\approx g[/math]

 

So yes, the g you mention is the acceleration we are exerted to by the force which fundamentally pulls us towards earth (but also pulls earth towards ourselves, but in a quite negligible way (try to find out the acceleration we exert on earth by pulling it towards ourselves), as is proven by Newton.

 

Luckily enough we can withstand this force and its acceleration with our muscles.

 

Note that as the distance between yourself and earth increases, the force by which you are attracted towards it will decrease exponentially, as will the acceleration you would be subjected to, so at a certain distance, it may become negligibly small, but it will never be 0.

Edited by Function
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What are you on about? Centrifugal force and gravity are two seperate things.

 

Now, according to general relativity, gravity isn't a force as such, it is the curvature of spacetime, which is why objects gravitate around it. You are mistaken about gravity not being attractive, because everything that spins exhibits the centripetal force which keeps the less massive objects spinning around the larger mass without them bumping into each other.

 

If there was no centrifugal and centripetal force, the two objects would surely collide. Gravity is attractive and it is foolish to claim otherwise.

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#2 Function

 

1.

Sounds great!

We've got a "constant" G,

with a very exact value.

I haven't a clue where it came from
but (I guess that's the way Newton set up the formula),

it proves everything anybody wants to know

(except me).

 

2.

The acceleration we "exert?" on the earth

is "opposite" & equal (=the same).

(I suspect you mean "pressure" instead, when both earth & you (=we) touch?)

 

3.

"So surely the force is attracting"

seems to be based on Newton,

who "assumed" it's attractive.

That's NO proof for me,
that's a preference,

that's an assumption.

(It does NOT exclude 1 direction.)


#3 Lord Antares

 

I cannot quite follow you.

Everything that is spinning tends to centrifuge (outward).

It's the atomic bonds

that keep things together,

& pulls things in(ward) centripetally,

while they (=the (large) objects) spin.

A spinning centrifuge sends the more massive outwards, NOT inwards.

=The less massive remain near the middle (NOT outwards).

Your explanation sounds reversed (=backwards) to me (if the less massive go outwards).

 

E.g. Freeze drying: the (lighter) water surfaces as ice (is not the cause of spinning).

 

What I'm onto?
Wiki states gravity is NOT a force (said bluntly),
I found that in their centrifugal force page.
Relativity confirms that,

(but I'm not interested in its (=Einstein's) reason (=assumption) being: volume moving in a curve,

by "multiplying" distance with time (as a factor), instead of "dividing" (for speed, as a quotient);

because that's too (spastic=abstract) wasteful & imprecise, for my fantasy).

 

Claiming "foolishness" is NO proof for me,

that's NOT what I'm looking for.

 

I need something to bite on. e.g. tangible.

 

=At present with all these assumptions,

you're still guessing.

Edited by Capiert
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#3 Lord Antares

 

I cannot quite follow you.

Everything that is spinning tends to centrifuge (outward).

 

Your explanation sounds reversed (=backwards) to me (if the less massive go outwards).

 

 

And where did I say it is otherwise? I said the centripetal force keeps the objects in orbit around the larger mass. Where did I give the reversed explanation?

 

Also, no, according to general relativity, gravity isn't a force, so I'm not sure that you think you are on to. This has been told for years.

 

Imagine you have two balls on a perfectly straight stripe of cloth held by the two edges. If you put your finger into the middle to dent the cloth, the balls will start moving towards each other. So this is not an attractive force as such, but you could say the net effect is attractive, if that makes sense to you.

 

You are not saying anything new.

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And where did I say it is otherwise?

..everything that spins exhibits the centripetal force which keeps the less massive objects spinning around the larger mass..

I said the centripetal force keeps the objects in orbit around the larger mass. Where did I give the reversed explanation?

In the word "spin" connected with centripetal, instead of centrifugal.

But some things fly apart, e.g. Roche limit,

when rotated too fast.

I suppose they are no longer spinning, if they have broken apart,

but centripetal force does NOT keep them together.

(=The smaller mass(ives) do NOT stay bound

to the more massives.

So your statement was wrong (for me, sometimes), implying (perhaps) things you did not notice.)

The centripetal law does NOT seem to dominate (for all cases).

The major (not minor)=general rule seems to be centrifugal, instead.

 

Also, no, according to general relativity, gravity isn't a force, so I'm not sure that you think you are on to.

? What? Please finish your statement.

This has been told for years.

 

Imagine you have two balls on a perfectly straight stripe of cloth held by the two edges. If you put your finger into the middle to dent the cloth, the balls will start moving towards each other. So this is not an attractive force as such, but you could say the net effect is attractive, if that makes sense to you.

 

 

Naturally, that makes sense to me.

Such examples are the best.

You are not saying anything new.

Say it this way:

We've been told for years

that centrifugal force is a force,

but now it's NOT!

Take it 1 step further.

Gravity is also NOT a force.

Well then, if that (force concept) was wrong before,

then is the "direction" of gravity still correct

(considering the force concept

was previously wrong)?

I'm only questioning the integrity of physics

considering it was wrong before.

That's nothing new.

Edited by Capiert
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You've got me there,

the mass in a rotating object

has non_linear acceleration,

which keeps rotating.

 

What I'm trying to figure out (in that question)

is the word net.

I assumed, centrifugal & centripetal accelerations balanced for circular motion.

If you're asking me, is the string tight in Newton's twirling water bucket pair experiment?

The answer is yes.

& that tightness seems (rather) constant for a given speed, but varies with speed.

 

But can rotation decrease (apparent) weight?

Edited by Capiert
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#2 Function

 

1.

Sounds great!

We've got a "constant" G,

with a very exact value.

I haven't a clue where it came from

but (I guess that's the way Newton set up the formula),

it proves everything anybody wants to know

(except me).

 

 

G is just a constant of proportionality (because of the arbitrary units we use for measuring things). It is determined by experiment. (It actually isn't known very accurately because it is hard to measure.) If you choose the right units, it disappears.

 

 

 

3.

"So surely the force is attracting"

seems to be based on Newton,

who "assumed" it's attractive.

That's NO proof for me,

that's a preference,

that's an assumption.

(It does NOT exclude 1 direction.)

 

It is not an assumption. It is just based on observation. We only ever see masses attract one another (apples falling from trees, planets orbiting the sun, etc). If we ever see gravity pushing things apart then we will have to update our theory.

 

 

 

Wiki states gravity is NOT a force (said bluntly),

I found that in their centrifugal force page.

Relativity confirms that,

 

It depends how you model it. In Newton's formula it is a force. In GR it is not.

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Thanks for your answers Strange.

But I'm still not clear on this (modeling).

E.g. Either something is, or is not.

Is gravity a force, or NOT?

Assuming GR is newest (theory)

(then (now) gravity is not a force?)

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It is physics. It is just about modelling/describing how things work. You can have multiple models of the same thing (that work in different cases).

 

What it "really" is (and if reality exists) is a question for philosophy, not physics.

Edited by Strange
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"So surely the force is attracting"

seems to be based on Newton,

who "assumed" it's attractive.

That's NO proof for me,

that's a preference,

that's an assumption.

(It does NOT exclude 1 direction.)

#3 Lord Antares

 

I cannot quite follow you.

Everything that is spinning tends to centrifuge (outward).

It's the atomic bonds

that keep things together,

& pulls things in(ward) centripetally,

while they (=the (large) objects) spin.

A spinning centrifuge sends the more massive outwards, NOT inwards.

=The less massive remain near the middle (NOT outwards).

Your explanation sounds reversed (=backwards) to me (if the less massive go outwards).

 

 

Yes, Newtonian gravity is a pull. That's the model, and the model works. If you want to model it as a push, feel free to develop that model. We will be glad to tear it apart.

 

When analyzing rotational motion using Newtonian physics, there is no centrifugal force. IOW, there is no outward radial force.

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Thank you Strange,

I'm surprised to notice how distant physics is

from physical reality.

That's a paradox for me,

why get physical at all?

Or should I better ask,

are you dealing physical or not.

Still, it's informative.

--

Thank you Swansont for your sturdy words.

At least I (now) know how things will go, in advance.

I expected you would be glad to help (model),

but it seems I was wrong,

the intent is destructive instead.

I still appreciate the honest words.

 

I think you also mean,

there is only an inward force

for rotation?

 

But I'd also appreciate

if you could answer my question

about gravity (in general);

not just Newton's gravity

(based on the greek's pull),

if that is possible?

(I suspect you will agree

gravity in general is also a pull?)

 

--

 

Thank you Function for your noble efforts,

I'm sorry they didn't fullfill what I needed.

--

 

Cheers, Lord Antares.

Edited by Capiert
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Thank you Strange,

I'm surprised to notice how distant physics is

from physical reality.

 

 

Even though I said "based on observation" ?

How much more physical than that can you get.

 

What science doesn't do is deal in metaphysics (e.g. "what is reality"); that is a question for religion or philosophy. By definition it is not empirically testable.

Edited by Strange
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We can only measure and interpret what we perceive: reality as it does present itself towards us. What we measure, interpret and formulate theorems on is perhaps not reality, but merely a best guess of reality: the manner in which it shows itself to us.

 

And whether you like it or not, we could never do better than that.

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"All I observe is,

gravitational acceleration "g is only an acceleration"."

If gravity is an acceleration then you have been accelerating at that rate for a long time.

10m/s/s

600m/s/min

36000 m/s/hr

864000 m/sec/day

and (neglecting relativity) about the speed of light after a year or so.

Are you moving away from your antipodean cousins at roughly the speed of light?

If so, how can you get news broadcasts from them?
If not, it's clearly not an acceleration- so it must be, in effect, a pull.

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Hi John

 

The acceleration (theory) does not bother me,

because of the expansion of matter (theory)

is its cause.

Whatever distance (that will be) measured

will also increase in size.

Doubling rate (period) ~19.6 min.

 

Thus, speed of light stays significantly the same.

 

You wouldn't notice your own growth

unless looking at (some) distant galaxies

which would appear to shrink (a bit).

 

But my underlieing question on all is,

is there a(n experimental) method

to determine (the direction)

whether (gravity is either) push or pull?

I don't know of 1 (yet?).

Edited by Capiert
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Hi John

 

The acceleration (theory) does not bother me,

because of the expansion of matter (theory)

is its cause.

Whatever distance (that will be) measured

will also increase in size.

Doubling rate (period) ~19.6 min.

 

Your comments always remind me of short poems.

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When Newton looked at gravity, he looked at space as the framework for everything that happens in the cosmos. Newton thought space was passive, absolute, eternal, and unchanging. Space and what happens in space were separate. The action could not effect space and space could not effect the action. In Newton's view of space, objects go through space in a straight path unless accelerated by a force to change that path. So when he saw planets going around the Sun, he naturally assumed that in an unchanging space there had to be a force acting on the planets to change their path through space that accelerated them toward the Sun.

Then came Einstein with a radical new approach. Space was not static and unchanging. It was dynamic and had a geometry that could bend, twist and ripple. Massive objects in space had a property that could cause bends, twists and ripples in space. This property of space Einstein realized was Gravity. Gravity was not a force in the sense of the other forces that were known. It was the change in the geometry of space itself. Objects were traveling in a straight line in curved space. Gravity was not a force that caused an acceleration to change a path in space, it is space itself that was curved and object were following a straight path in curved space. So although Gravity may appear to take look like a force, it is really a property of space. Does this help?

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The acceleration (theory) does not bother me,

 

because of the expansion of matter (theory)

is its cause.

Whatever distance (that will be) measured

will also increase in size.

Doubling rate (period) ~19.6 min.

 

 

 

What is the 'expansion of matter theory' ? Also what is doubling rate and where did you get that value from ?

 

But my underlieing question on all is,

is there a(n experimental) method

to determine (the direction)

whether (gravity is either) push or pull?

I don't know of 1 (yet?).

 

 

Push and pull are really relative terms though. Locally, a gravitational field can appear to push or pull depending on your frame of reference. You need to provide some substantial maths to back up the claim that it is one over the other.

Edited by Royston
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Does this help?

Yes, but I (still) have to interpret some (quite a bit)

so I can understand it in my (perspective) terms.

Marvelous description, though.

I like how you are highlighting, the controversial themes (=differences),

in comparison to natural thinking (expectations).

 

Thank you.

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Hi Royston

What is the 'expansion of matter theory' ?

It's a side effect (further conclusion) of Hubbles expanding universe.

 

Also what is doubling rate and where did you get that value from ?

It's the duration time, needed for matter to double its size wrt an absolute (space),

(in our solar_system).

Pick a point above the earth's surface,

1 earth radius away.

Calculate the falling time,

(a mass needs, from that height)

till it reaches the earth's surface.

That's the same amount of time needed

(if the frames were reversed)

for the earth's surface

to expand up

till it reaches that point.

Push and pull are really relative terms though. Locally, a gravitational field can appear to push or pull depending on your frame of reference. You need to provide some substantial maths to back up the claim that it is one over the other.

And you do too (please). I do not have maths to exclude either. Perhaps you do? Edited by Capiert
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