An object at rest "tends" to stay at rest?

[Baby Astronaut]

Isn't that a bit oddly written? Seems like a popularization.

 

Newton's First Law (also known as the Law of Inertia) states that an object at rest tends to stay at rest and that an object in uniform motion tends to stay in uniform motion unless acted upon by a net external force.

 

If it is just a popularization, I'm unsure why it had to say "tend" when it's more accurate to say "object at rest stays at rest and that an object in uniform motion stays in uniform motion unless acted upon by..."

 

Otherwise, it implies that an object doesn't always stay at rest or in motion even if it weren't acted upon by an external force.

 

Plus it says nothing about an internal force. I can imagine a ball with a propulsion device inside firing a small object at its inside, causing it to begin rolling.

 

Just something I wondered about.

[Mokele]

Could it just be translation, since the original was written in Latin?

[insane_alien]

Lex I: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare.

 

Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.

 

what newton actually wrote and its translation.

 

the tends slipped in there when someone tried to put it into modern english and failed.

 

the one i always seen was 'an object remains at rest or in uniform motion unless acted upon by an unbalanced external force'

[swansont]

I can imagine a ball with a propulsion device inside firing a small object at its inside, causing it to begin rolling.

 

 

How would it do so?

[Baby Astronaut]

How would it do so?

Like so.

 

I can't draw

 

However, this next image perfectly illustrates what I mean by an object being acted upon by an internal force.

 

 

Say hello to the cute hamster, the newest physics volunteer experimenting for science.

[swansont]

You're looking at rotation and composite systems. Newton's laws are meant to be applied to linear motion of rigid bodies, though there is an analogous set of laws for rotation. Even so, if the body is the shell of the ball, the cannon/cannonball or mouse are external forces.

 

The danger in looking at composite systems and is that you may leave a component out, like the earth, which is also exerting a force on the system. If you look at that whole system, the motion is unchanged.

[Mokele]

Also, technically a hamster ball only works with an external force: friction. If there's no friction to prevent the ball slipping against the substrate, the hamster will only succeed in spinning the ball around, generating no forward movement.

 

As for the gun, remember that guns have recoil. Equal and opposite.

[swansont]

Also, technically a hamster ball only works with an external force: friction. If there's no friction to prevent the ball slipping against the substrate, the hamster will only succeed in spinning the ball around, generating no forward movement.

 

As for the gun, remember that guns have recoil. Equal and opposite.

 

And the friction is supplied by the earth (or whatever surface is attached to it), so what Mokele has said is another (more specific) view of what I did.

[Baby Astronaut]

Also, technically a hamster ball only works with an external force: friction. If there's no friction to prevent the ball slipping against the substrate, the hamster will only succeed in spinning the ball around, generating no forward movement.

Good point, but now it attracts a new observation.

 

swansont mentioned how an analogous set of laws exists for rotation. Is it possible these laws are further collapsible into one with Newton's laws of motion?

 

I mean, if a spinning ball on a frictionless surface would continue its state forever, then I'd imagine it's in a kind of static motion, but motion nonetheless. Thus all you'd have to do is remove the "straight forward" criteria from insane_alien's quoted translation of Newton's First Law, perhaps, to merge them into one law. I could be wrong since I'm less familiar with the rotation laws.

 

As for the gun, remember that guns have recoil. Equal and opposite.

Well, the gun isn't attached to the base. It would fall soon as the ball rolled forward enough. However, it would be enough to get the ball rolling. And if it were next to top edge of a steep hill...

[Sisyphus]

 

swansont mentioned how an analogous set of laws exists for rotation. Is it possible these laws are further collapsible into one with Newton's laws of motion?

 

Yes. It involves calculus. You treat objects as collections of infinitesimal connected point-objects exerting forces on one another, each point is in continually accelerated by the others, bla bla bla. It's far easier to use rotational equivalents.

 

Well, the gun isn't attached to the base. It would fall soon as the ball rolled forward enough. However, it would be enough to get the ball rolling. And if it were next to top edge of a steep hill...

 

Whether or not the gun is attached, it would be impossible to change the ball-gun system's center of mass by any internal action. If it's not attached, then the gun flies backwards with as much force as the bullet flies forwards.

[PlayStationX]

"object at rest stays at rest and that an object in uniform motion stays in uniform motion unless acted upon by..."

 

you are right. its badly worded, too many words.

 

it should go like this:

-an object in uniform motion stays in uniform motion unless acted upon by force

 

 

1.) not "external force", any force

 

2.) mentioning object at rest is not important, it is still "uniform motion", only with zero velocity

 

 

 

maybe better yet, it should go like this:

- only force can accelerate objects

 

 

...may the force accelerate you!

Edited January 13, 2009 by PlayStationX

[Baby Astronaut]

you are right. its badly worded, too many words.

 

it should go like this:

-an object in uniform motion stays in uniform motion unless acted upon by force

I like where you're heading. Maybe it can be broken down even further.

 

"Uniform motion is perpetual unless acted upon by a force"

[PlayStationX]

"Uniform motion is perpetual unless acted upon by a force"

 

i agree with that.

 

 

but lets analyze it,

what is that sentence about, some motion and force?

 

 

well, i believe it is about 'CHANGE in MOTION' aka ACCELERATION.

 

 

 

so what can you possibly say about acceleration and force?

 

1.) force can cause acceleration (force accelerates)

2.) force always causes acceleration (force always accelerates)

3.) only force can cause acceleration (only force accelerates)

 

i think its #3, thought it sounds more trivial and even questionable

Edited January 13, 2009 by PlayStationX

[swansont]

you are right. its badly worded, too many words.

 

it should go like this:

-an object in uniform motion stays in uniform motion unless acted upon by force

 

Isn't circular motion at constant speed "uniform" ?

[PlayStationX]

Isn't circular motion at constant speed "uniform" ?

 

i agree that question is valid. it goes on to show how original formulation is vague.

 

 

this is the essence of it cut with Occam's razor:

- only force accelerates

 

 

still, circular motion with constant velocity leaves a question - is there really some acceleration in there, or is it just a curvature in space-time?

[npts2020]

I think what swansont is trying to point out, is that direction is uniform as well as speed and you have to account for it. e.g. planets do not follow the curvature of space but have uniform (relatively) motion.

[swansont]

i agree that question is valid. it goes on to show how original formulation is vague.

 

 

this is the essence of it cut with Occam's razor:

- only force accelerates

 

 

still, circular motion with constant velocity leaves a question - is there really some acceleration in there, or is it just a curvature in space-time?

 

Actually my objection is to your shortening of the statement. And there is no circular motion at constant velocity, by definition — velocity is a vector.

 

——

 

From wikipedia, (and quoted by insane_alien above) the first law is:

 

Lex I: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare.

 

Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.

 

i.e. "uniform motion" is defined, and not ambiguous

 

http://en.wikipedia.org/wiki/Newton's_laws_of_motion#Newton.27s_first_law:_law_of_inertia

 

———

 

 

In regard to the OP, I suspect the word "tend" may have some ties to the notion that Newton displaced, which was that an object's natural tendency was to come to rest, i.e. that was a dynamic thing. Moving objects tend to come to rest. The translation of Newton is saying that no, it's only objects already at rest that tend to remain that way, and they do not start to move on their own, i.e. there is no tendency for spontaneous motion: motion from a state of rest requires a force.

[PlayStationX]

Actually my objection is to your shortening of the statement.

 

ok, i want to claim that "only force accelerates", contains all the information of the original statement, plus some more information, which makes it better definition. i want to claim that this short statement can substitute the original statement, completely and in every case.

 

 

 

And there is no circular motion at constant velocity, by definition — velocity is a vector.

 

i agree definition is such, i was referring that to lead these two statements in contradiction:

 

1.) when light bends due to gravity, it does not accelerate - it follows curvature of space-time

 

2.) magnetic field can not accelerate charged particles, but still it can change their direction

 

 

 

"uniform motion" is defined, and not ambiguous

 

i agree. it is explained, that if you read original text you may notice that he means constant velocity as well as constant acceleration. but when making new, modern formulation why not make it crystal clear. why not call "change in motion" - acceleration, we have a name for it, why not use it? why make it confusing? whats the point of words "tend", "external", "unbalanced"?

 

the sentence does not have "focus", its hard to see what is it about and why is it important. it kind of tries to be about "frames of reference" while it can not be about anything else but the force, since the "force" is a 'primary' word needing description.

 

 

In regard to the OP, I suspect the word "tend" may have some ties to the notion that Newton displaced, which was that an object's natural tendency was to come to rest, i.e. that was a dynamic thing. Moving objects tend to come to rest. The translation of Newton is saying that no, it's only objects already at rest that tend to remain that way, and they do not start to move on their own, i.e. there is no tendency for spontaneous motion: motion from a state of rest requires a force.

 

word "tend" has no place in there, it gives no explanation for anything , it only makes statement more undefined. it makes you feel as if there is some threshold to which object resist to change motion.

 

it is as if some more inert objects will not react at all, it makes you think that some minimal force will produce no effect what so ever, or that is a matter of chance.

 

definition should use words like: all, none, never, always, only...

 

 

...Galileo realized that force acting on a body determines acceleration, not velocity. This insight leads to Newton's First Law—no force means no acceleration, and hence the body will maintain its velocity.

http://en.wikipedia.org/wiki/Newton_third_law

 

this sums up my line of thought

Edited January 13, 2009 by PlayStationX

[swansont]

The objection I have to that is that it ignores the historical view, and appears to assume that the galilean/Newtonian view is obvious. But if it were so obvious, why did the Aristotalean view persist for 2000 years? And the OP did not ask if "tend" should be there, rather it asked why it was there.

 

All the rest is, I think, semantics and opinion. Is there a quantifiable way to show that one statement is better than another?

Edited January 13, 2009 by swansont
fix typo

[Klaynos]

I'd like to take this opertunity to remind one and all of rulse 2.10 and 2.5 that requires that personal ideas/speculations are posted in the correct forum and in not in science threads, and also that new discussion threads are put into new threads, this will lead to a better experience for all and a better discussion of both ideas.

 

This is just a reminder as I can see it wandering in that direction.

[PlayStationX]

Is there a quantifiable way to show that one statement is better than another?

 

of course there is, the statement that leaves less room for misinterpretation is better. also, according to Occam - simplest solution is the best. the fact that you simply can not go wrong with this one, makes it perfect: -"only force accelerates."

 

 

but i combined all three laws in one:

- only force accelerates and unless opposed by equal force, it always does so. F= m*a

 

 

 

Klaynos,

 

This is just a reminder as I can see it wandering in that direction.

 

im not sure if that was towards me, can you point out what you mean?

 

in any case, im just trying to discuss semantics, definitions and their meaning. i do not propose new definition, im just explaining what it really means, its pure logic and semantics, usage, meaning and interpretation of the words, thats what this thread is about, i gather.

 

i insist that my definition does NOT lose applicability nor any information of original, but only makes it more clear.

Edited January 13, 2009 by PlayStationX

[Baby Astronaut]

I'd like to take this opertunity to remind one and all of rulse 2.10 and 2.5 that requires that personal ideas/speculations are posted in the correct forum and in not in science threads, and also that new discussion threads are put into new threads, this will lead to a better experience for all and a better discussion of both ideas.

I actually think the "new" direction is relevant.

 

More importantly, the only speculation we've had is in determining the significance of an original choice of wording.

 

Seeing if you can reduce a statement to its bare essentials, and considering it's a scientific one, I think is a good exercise to develop a well-constructed vision of its mechanics.

 

Isn't it valid to discuss changes in the way science is taught, if we alter none of its conclusions in any way, but instead manage to clarify them?

 

Martin attempted a philosophy of science area, where maybe the thread would fit better. I don't think it's a good idea to split it though, for the context might be lost or diluted.

 

The objection I have to that is that it ignores the historical view, and appears to assume that the galilean/Newtonian view is obvious. But if it were so obvious, why did the Aristotalean view persist for 2000 years? And the OP did not ask if "tend" should be there, rather it asked why it was there.

Maybe a historical science branch is needed today, where one can investigate how science has evolved throughout the ages, without its mixing into contemporary understanding.

 

All the rest is, I think, semantics and opinion. Is there a quantifiable way to show that one statement is better than another?

Not with equations, but yes.

 

1. The science establishment can select a group to unanimously determine that a reduced statement doesn't omit anything necessary and has less potential confusion.

 

2. It's tested with newbies and students alike to verify that no confusion has occurred with its intended meaning.

 

 

of course there is, the statement that leaves less room for misinterpretation is better. also, according to Occam - simplest solution is the best. the fact that you simply can not go wrong with this one, makes it perfect: -"only force accelerates.".

It can go wrong. A person might think the force itself is the only thing able to accelerate.

 

Force alone causes acceleration.

 

Simplified one more notch: Force causes acceleration.

 

As you can see, however, it doesn't explain that velocity maintains its state.

 

"Uniform motion is perpetual unless acted upon by a force"

I'm not sure if that even covers it. Perhaps the statement below.

 

"Within any frame of reference: a state of rest or uniform velocity is perpetual unless acted upon by a force"

 

Keep in mind that we can go too far in simplifying and then it's counterproductive. We'd have to test the new statement with people to ensure no accuracy/meaning is lost on the other end.

[PlayStationX]

It can go wrong. A person might think the force itself is the only thing able to accelerate.

 

what else can accelerate?

 

 

Simplified one more notch: Force causes acceleration.

As you can see, however, it doesn't explain that velocity maintains its state.

 

hey, i like the way you think.

 

i want to say: -"only force accelerates",

because i think this additional information stands as true, is there any equation that has acceleration, but not 'force' in it?

 

 

i think it maintains velocity is constant (without introduction of forces to system),

since for velocity to change there need to be some acceleration. in other words it means: "without applied force velocity will not change, because ---> only force causes acceleration.", only force can change velocity and/or direction.

 

 

curvature of space-time can too perhaps, but that is another theory and is still some "force", thought represented geometrically.

Edited January 14, 2009 by PlayStationX

[Baby Astronaut]

It can go wrong. A person might think the force itself is the only thing able to accelerate.

what else can accelerate?

"Only force accelerates" can imply an unintended meaning.

 

_________________________________

I am a force.

I can accelerate myself.

Nothing else can accelerate itself.

_________________________________

 

It's very possible I'm wrong, but the only method of knowing for sure is to test it out.

 

Can't answer your one question, since I'm unaware if an equation that contains acceleration but not force exists.

[PlayStationX]

"Only force accelerates" can imply an unintended meaning.

 

all three words are very intended, what do you mean?

 

 

the "force" was conceived as abstract concept.

we can see material world and how particle move and how they interact, but we were never able to see what moves them. later on we figured, it ultimately all boils down to some electromagnetic fields. that didn't solve the problem as these fields still seemed to be immaterial, spiritual, incorporeal. and so, we still can not "see" them and we still don't know what are they made of.

 

nevertheless, we wanted to talk about it and so we gave it a name - "force", as in "making something to do something", "influencing", "acting upon"... "Only force accelerates", the truth about that only "force" can do it comes out of the very definition and necessity for the word, which then makes it unnecessary to mention. still, i like it because it seems as "bold statement", while its actually a matter of semantics.

 

 

i share your interest about the history of science.

Edited January 14, 2009 by PlayStationX