Jump to content
PrimalMinister

Could relativity be incorrect

Recommended Posts

5 hours ago, mistermack said:

No external source of energy is needed for a constant rotational acceleration. It could continue for ever without any input. 

No, not true for a rigid body.

Share this post


Link to post
Share on other sites
On 11/08/2017 at 8:30 PM, mistermack said:

No external source of energy is needed for a constant rotational acceleration. It could continue for ever without any input. 

On 12/08/2017 at 2:14 AM, swansont said:

No, not true for a rigid body.

mistermack didn't say "rigid body"... anyway, that's an interesting assertion; please clarify!

Share this post


Link to post
Share on other sites
1 hour ago, Tim88 said:

mistermack didn't say "rigid body"... anyway, that's an interesting assertion; please clarify!

No, but in an assertion of something without any constraints, i.e. something that's offered as being generally true; all you need is a counter-example to show it to be false. A rigid body in free space cannot undergo a constant rotational acceleration without an energy input. Angular momentum and energy are conserved. Is that sufficient clarification? (I would have thought this to be obvious, and uninteresting)

Share this post


Link to post
Share on other sites
10 hours ago, swansont said:

No, but in an assertion of something without any constraints, i.e. something that's offered as being generally true; all you need is a counter-example to show it to be false. A rigid body in free space cannot undergo a constant rotational acceleration without an energy input. Angular momentum and energy are conserved. Is that sufficient clarification? (I would have thought this to be obvious, and uninteresting)

How rigid does it have to be, to need an energy input?

Share this post


Link to post
Share on other sites
1 hour ago, mistermack said:

How rigid does it have to be, to need an energy input?

You can make an object spin faster without energy input by lowering the moment of inertia. Figure skaters do this. But to do this continually, the object has to keep getting smaller. That has obvious limits.

Share this post


Link to post
Share on other sites
1 hour ago, swansont said:

You can make an object spin faster without energy input by lowering the moment of inertia. Figure skaters do this. But to do this continually, the object has to keep getting smaller. That has obvious limits.

Figure skaters moving their arms closer to the body requires work to be done by the arms. External energy input could used for a similar result.

Share this post


Link to post
Share on other sites
21 hours ago, swansont said:

No, but in an assertion of something without any constraints, i.e. something that's offered as being generally true; all you need is a counter-example to show it to be false. A rigid body in free space cannot undergo a constant rotational acceleration without an energy input. Angular momentum and energy are conserved. Is that sufficient clarification? (I would have thought this to be obvious, and uninteresting)

Probably you misunderstood him. He was comparing constant straight line acceleration with constant centripetal acceleration (= in a circle, or "rotational"):

Quote

Travelling in a circle is a different kind of acceleration though. It's not continuous, but constantly changing in direction.

In contrast to rectilinear acceleration, there is no energy input.for the simple case of a body that is freely rotating at constant centripetal acceleration (constant rotation speed).

Share this post


Link to post
Share on other sites
1 hour ago, Tim88 said:

Probably you misunderstood him. He was comparing constant straight line acceleration with constant centripetal acceleration (= in a circle, or "rotational"):

Centripetal acceleration is not rotational acceleration. They are not the same thing. Why is it my misunderstanding instead of his misuse of terminology? (and why does it fall to you to be the interpreter and apologist?)

10 hours ago, Carrock said:

Figure skaters moving their arms closer to the body requires work to be done by the arms. External energy input could used for a similar result.

Yes, you are correct (that occurred to me after I posted. Iw is constant. Iw^2 has to increase. I was only thinking of an external influence, but it's incorrect to limit the source). So even that is not an exception.

Share this post


Link to post
Share on other sites
5 hours ago, swansont said:

Centripetal acceleration is not rotational acceleration. They are not the same thing. Why is it my misunderstanding instead of his misuse of terminology? (and why does it fall to you to be the interpreter and apologist?)

My meaning should have been clear from the context. It was to Tim88.  I didn't write angular acceleration, and the fact that I wrote that it could continue for ever without energy input should have made it perfectly obvious what I was referring to. 

Seems more like a case of deliberate misunderstanding. 

Share this post


Link to post
Share on other sites
33 minutes ago, mistermack said:

My meaning should have been clear from the context. It was to Tim88.  I didn't write angular acceleration, and the fact that I wrote that it could continue for ever without energy input should have made it perfectly obvious what I was referring to. 

No, you wrote rotational acceleration. Rotation being the change in the angle, and the speed measured by omega. It is not synonymous with centripetal acceleration. 

Quote

Seems more like a case of deliberate misunderstanding. 

I simply took you at your word, and assumed you meant what you said. That I did not properly decipher that when you posted one thing you meant something very different is not something that I am willing to accept blame for. It was your error. Own it.

Share this post


Link to post
Share on other sites
1 hour ago, swansont said:

I simply took you at your word, and assumed you meant what you said. That I did not properly decipher that when you posted one thing you meant something very different is not something that I am willing to accept blame for. It was your error. Own it.

No you didn't. You knew what was meant but get a pleasurable little kick out of contradicting people.

I certainly don't begrudge you those little moments if it makes you happy.

Share this post


Link to post
Share on other sites
31 minutes ago, mistermack said:

No you didn't. You knew what was meant 

No, I absolutely did not. It did not occur to me that you were talking about centripetal acceleration rather than rotational acceleration when you wrote rotational acceleration. I can't read your mind. I can only go by what you say. I try very hard not to assume you (or anyone) means anything other than what you post.

I was trying to explain physics to someone who said that he didn't know gravity was not caused by the earth's rotation. It's not out of the pale that you had some other misconceptions, too.

Share this post


Link to post
Share on other sites
On 8/5/2017 at 10:18 AM, imatfaal said:

Not sure that your question isn't a false dichotomy. 

Firstly we like relativity as an explanation as the calculation of the expected time dilation via the schwarztchild metric was predicted and then found to be accurate; it is always better when it is this way around. 

Secondly, your wording is dubious - time is dilated, clocks which are running normally in their own frame, can tick slower or faster when viewed from a different frame which is in relative motion, at a different gravitational potential, or both in the case of an orbitting satellite.  You need to be very careful when using terms like travelling into the future - it is the marrying up of linguistic terms like that and the mathematical formalism of the physical theory which causes many of the problems of understanding.   Clocks at a higher gravitational potential tick faster when viewed from the persepective of a local frame at lower gravitational potential and vice versa.  Clocks in relative motion tick slower when viewed from the local frame which the observer deems to be at rest.  "Travelling into the future" does that mean the same?

One thing that is certain is we are all traveling forward through time, and are thus time travelers. If time is a variable that slows down or speeds up, then relativity has a fundamental flaw, because how fast light travels in a given frame of reference would always be different than in another and the given velocity of light would be variable when observed from different perspectives, but what we see instead is that it is a constant in all frames of reference and observation.

On 8/17/2017 at 0:42 PM, swansont said:

No, I absolutely did not. It did not occur to me that you were talking about centripetal acceleration rather than rotational acceleration when you wrote rotational acceleration. I can't read your mind. I can only go by what you say. I try very hard not to assume you (or anyone) means anything other than what you post.

I was trying to explain physics to someone who said that he didn't know gravity was not caused by the earth's rotation. It's not out of the pale that you had some other misconceptions, too.

While gravity is not created by the Earths rotation, it's overall force is most certainly affected by that rotation and the centripetal acceleration that results. I'm not sure how helpful this is but motion affects gravity and can create artificial gravitational effects. Eventually gravity will be understood as an effect of electrostatic attraction between dissimilar charged particles in matter , but that is another thread

On 8/17/2017 at 10:41 AM, swansont said:

No, you wrote rotational acceleration. Rotation being the change in the angle, and the speed measured by omega. It is not synonymous with centripetal acceleration. 

 

Pardon me for my confusion, but one of the force vectors created by a rotational acceleration IS indeed centripetal acceleration. While acceleration of the rotation is not necessary for the force of centripetal acceleration to exist, it DOES indeed directly effect its value and if no rotational acceleration had ever existed there would be no centripetal acceleration. They're not the same thing exactly obviously but are intrinsically linked, which you seem to be unaware of.

While it isn't a proper scientific nomenclature, how fast something is rotating around a central point or changing position does indeed have a direct correlation to the centripetal acceleration that acts on said object or mass. Take the example of a simple flywheel, when torque is applied it's rotational velocity increases and the force created by centripetal acceleration increases. Without rotation, no centripetal acceleration can exist. it might be rotation of a fixed mass or one mass around another held in orbit by gravity, a mechanical link or any number of ways.

On 8/17/2017 at 10:12 AM, mistermack said:

My meaning should have been clear from the context. It was to Tim88.  I didn't write angular acceleration, and the fact that I wrote that it could continue for ever without energy input should have made it perfectly obvious what I was referring to. 

Seems more like a case of deliberate misunderstanding. 

In a discussion involving any subject it is critical to always use correct terminology and nomenclature to describe a given component of your thoughts. Language is the commonality we all use to understand each other. The problem with what you said is no two people could likely be certain what it was exactly. That being said, YOU ARE NOT ALONE! There are many so called theories in science and especially physics that no two people have the same understanding of . but in that case it is simply because they don't really make any sense and defy logic or conventional wisdom. I think looking back on the 20th century, we will see it as a dark age of science where no one actually understood any of the widely touted "theories" in the same way. IMO for a theory to be valid, there must be some logical consensus about what said theory claims. The fact that it is testable using mathematics only proves it is an artificial mathematical construct, Hollywood in science..For a theory to be valid it has to be universally understood by those educated in the field of physics, and testable by conclusive experimentation that cannot be debunked through other explanations of the observed phenomenon.

Edited by Anonymous Participant

Share this post


Link to post
Share on other sites
6 hours ago, Anonymous Participant said:

If time is a variable that slows down or speeds up, then relativity has a fundamental flaw

Yes I agree with this because relativity is another way to postulate that spacetime is homogeneous and isotropic.

 

6 hours ago, Anonymous Participant said:

Eventually gravity will be understood as an effect of electrostatic attraction between dissimilar charged particles in matter

Many have sought to support this view but no one has yet offered any way to overcome several practical serious and fundamental observations that demonstrate differences between electrical attractions and gravity.

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.