I Battery life on VERY fast moving object

[davidjoe]

Speed, above, by me has been about a fraction if C. C is a certain distance per second, with seconds being accepted as a unit that is definite on earth. It’s not that it’s an absolute quantity, more that I’m just not interspersing different frames into the hypothetical.

 

[PeterDonis]

wouldn’t there be a reference frame where nothing at all impacts the time a clock keeps?

@PAllen's response is a good one, but I would add that there is no reference frame that is "absolute" in the sense you are implying here. There is no reference frame in which time, distance, speed, etc. are the "true" ones, "unaffected by dilation" or anything else.

Why would it not be possible to simply say that an object covers a 1 kilometer length without deviating, so as to trigger an accelerometer, per second, according to a clock that is unaffected by any form of dilation?

Because there is no such thing as "a 1 kilometer length" without it being relative to something. For example, if you put out a 1 kilometer long ruler and say that is "a 1 kilometer length", then you are measuring lengths relative to that ruler, which means relative to that ruler's rest frame. (And even that assumes that the ruler can be treated as a rigid body, which will not be true for all possible states of motion of the ruler or all possible spacetime geometries--if the ruler is being subjected to forces or is free-falling in a curved spacetime, it will not be a perfect rigid body.) There is no way to define "a 1 kilometer length" without choosing something tangible to refer it to.

once you knew that your clock was not synchronized with earth, you would have no idea by how much this was the case

Sure you can. You can determine your orbital parameters around Earth, and use that to compute the difference in clock rates. Indeed, that is exactly how GPS works: the orbital parameters of each GPS satellite are known with high precision, and that enables their clock rates relative to Earth clocks to be calculated with high precision--which in turn enables the signals from the satellites to be used by Earthbound GPS receivers to calculate position and time with high precision.

 

[PeterDonis]

C is a certain distance per second, with seconds being accepted as a unit that is definite on earth.

"Distance" in SI units is defined in terms of the speed of light having the defined value of 299,792,458 and the SI second defined in terms of a cesium hyperfine transition; there is no independent unit of "distance" in SI units.

In "natural" units, which are often used in relativity (I use them all the time when posting calculations here), $c$ is defined to be $1$.

 

[PeroK]

Speed, above, by me has beta about a fraction if C. C is a certain distance per second, with seconds being accepted as a unit that is definite on earth. It’s not that it’s an absolute quantity, more that I’m just not interspersing different frames into the hypothetical.

As you sit at your desk typing in your posts, what is your definite speed? How do you measure it?

 

[davidjoe]

As you sit at your desk typing in your posts, what is your definite speed? How do you measure it?

For me, measurement would be from the “birds eye” view, centering over my head, and I could draw larger and larger circles (going higher) to determine when I moved, relative to still things. Until the circle is continent size, I’m not seeing movement, then it’s tiny movement, then orbital movement and so on…

 

[PeroK]

For me, measurement would be from the “birds eye” view, centering over my head, and I could draw larger and larger circles (going higher) to determine when I moved, relative to still things. Until the circle is continent size, I’m not seeing movement, then it’s tiny movement, then orbital movement and so on…

Hmm? Legal arguments, it seems, are very different from mathematical arguments!

 

[PeterDonis]

For me, measurement would be from the “birds eye” view, centering over my head, and I could draw larger and larger circles (going higher) to determine when I moved, relative to still things.

What are "still things"? You're still assuming that something can be "still" in an absolute sense. It can't. There is no such thing. All motion is relative.

Until the circle is continent size, I’m not seeing movement, then it’s tiny movement, then orbital movement and so on…

What you actually mean here is: you are not moving relative to the Earth (at least not when you are sitting typing your posts at a desk--you would be if you were typing them on a bus or train en route between stops). But you are moving relative to the sun, and relative to the center of the Milky Way galaxy, and...

In other words, all motion is relative. There is no absolute sense in which you, or anything else, are "moving" or "still".

 

[davidjoe]

Hmm? Legal arguments, it seems, are very different from mathematical arguments!

I could say an accelerometer would tell me if I moved, but it’s not going to tell me speed. If I knew size of other things in the concentric circles, I could deduce my speed, relative to them.

I do get the point about “relative to other objects” being a way to describe my speed. But, technically, if I’m looking down at me, (a camera) and the earth I see moving around the sun, but all objects are removed, I still see the earth circling, and I didn’t need the other objects to determine that.

 

[PeterDonis]

I could say an accelerometer would tell me if I moved

No, it tells you whether or not you are being subjected to a force. An accelerometer attached to you as you sit at your desk, at rest relatve to the Earth, reads nonzero. (Nowadays smartphones make it easy to test this.)

I do get the point about “relative to other objects” being a way to describe my speed.

Then why do you insist on backing away from the point immediately?

But, technically, if I’m looking down at me, (a camera) and the earth I see moving around the sun, but all objects are removed, I still see the earth circling, and I din’t need the other objects to determine that.

Yes, you do--you need the camera. You are assuming that the camera is "at rest". But that's relative. Relative to the Earth, it's the camera that is moving and the Earth that is at rest.

In other words, no, you still have not truly grasped what "all motion is relative" means, because you are failing to account for the camera as an "object" like everything else.

 

[davidjoe]

How do you type so fast.

Relative to me.

 

[PeroK]

I could say an accelerometer would tell me if I moved, but it’s not going to tell me speed. If I knew size of other things in the concentric circles, I could deduce my speed, relative to them.

I do get the point about “relative to other objects” being a way to describe my speed. But, technically, if I’m looking down at me, (a camera) and the earth I see moving around the sun, but all objects are removed, I still see the earth circling, and I din’t need the other objects to determine that.

My point was that fundamentally we are talking at cross purposes. To take an analogy. The law is to some extent arbitrary, but a specific legal framework has been laid down. It's no good if someone comes along and wants to have their own personal definition of legal terms and what the law means.

Likewise, we can't have a sensible, practical discussion about physics without using an established common set of definitions and terminology. And, the onus is on you to learn and adopt the standard definitions of things like velocity and speed and reference frames. We can't discuss physics using your "homespun" definitions of things. That doesn't work at all and leads nowhere.

 

[davidjoe]

I think an accelerometer does not detect force, just movement. If I attached one to the base of the Empire State Building and then shoved on it, there’s force but no movement.

 

[davidjoe]

My point was that fundamentally we are talking at cross purposes. To take an analogy. The law is to some extent arbitrary, but a specific legal framework has been laid down. It's no good if someone comes along and wants to have their own personal definition of legal terms and what the law means.

Likewise, we can't have a sensible, practical discussion about physics without using an established common set of definitions and terminology. And, the onus is on you to learn and adopt the standard definitions of things like velocity and speed and reference frames. We can't discuss physics using your "homespun" definitions of things. That doesn't work at all and leads nowhere.

I do like what you are saying here.

I would say that complying with one law should not put one in the position of breaking another. Rarely, it can though, but usually not because laws are proscriptive. Feds say no MJ, state allows RX, what’s a doctor to do. But usually gets straightened out immediately if it does.

Physics seems to challenge me. For example. Can’t explain the speed of galactic motion - invent dark matter to explain it.

 

[PeroK]

Physics seems to challenge me. For example. Can’t explain the speed of galactic motion - invent dark matter to explain it.

That's an open question. Before Newton, Kepler's laws were known as an observable phenomeon by had no theory to explain them. Newton invented the force of gravity to explain them. This replaced "the hand of God"!

Now, galaxy rotational dynamics are an observable phenomenon. There are at least two theories put forward to explain them. Dark matter is one and MOND is another. This is the way science works.

 

[Sagittarius A-Star]

If two different speeds are calculated based on the passage of two different periods of time as measured by different clocks, then at least one of them cannot be correct.

A precondition that you can understand it is, that you first fully understand the relativistic calculation of the Sagnac-effect with respect to the rotating reference frame and the calculation of the Ehrenfest-"paradox".

Links:

1. http://www.physicsinsights.org/sagnac_1.html
2. https://en.wikipedia.org/wiki/Ehrenfest_paradox

Not everything what you don't fully understand must be incorrect.
Non-inertial (i.e. rotating) reference frames maybe more complicated than you think they are.

 

[jbriggs444]

I think an accelerometer does not detect force, just movement. If I attached one to the base of the Empire State Building and then shoved on it, there’s force but no movement.

They detect [non-gravitational] net force^(*). They are designed to be insensitive to stress, such as someone pushing on one side while the Empire State Building resists on the other.

[This is in contrast to a bathroom scale which is designed to be sensitive to the stress of feet pushing down on one side and the floor up on the other]

If you have attached an accelerometer to the base of the Empire State Building, it will detect a net force of magnitude $mg$ directed upward despite the lack of movement or acceleration relative to the local rest frame of West 34th Street.

You may have noticed that West 34th Street is not in free fall.

(*) To be pedantic, an accelerometer measures the stresses that are created in supporting a test mass. That test mass is buried inside the device and held approximately stationary by materials that can report their internal stress in some way (piezoelectric, piezoresistive or capacitive for instance). If you know the stress on the support material, you know the force on the test mass. If you know the force on the test mass, you know its acceleration. Since it is held approximately in place, the acceleration of the test mass matches the acceleration of the accelerometer. Which is what you wanted to know.

If the mass of the accelerometer as a whole is known then its acceleration relative to a free fall frame will be proportional to the non-gravitational net force on the accelerometer. In this situation, a measurement of acceleration and a measurement of non-gravitational external net force are one and the same thing. It is just a matter of how you calibrate the dial.

 

[PeroK]

You may have noticed that West 34th Street is not in free fall.

Wall Street was in free fall in 1929, but perhaps not West 34th Street.

 

[Nugatory]

I think an accelerometer does not detect force, just movement. If I attached one to the base of the Empire State Building and then shoved on it, there’s force but no movement.

Someone in free fall (and reasonably nearby) will find that the Empire State Building, foundations and all, is accelerating at 1g while they are at rest and their accelerometer is reading zero, no force because they’re free-falling. On what basis do you justify the claim that your perspective (no movement relative to you and the surface of the earth) is more “real” then the free-faller’s perspective (earth and building are moving towards them?

Before you answer, I’m going to add one more thing: the person you are trying to convince is an astronomer on Mars, sitting peacefully in their easy chair and watching through a telescope - so as far as they are concerned the free-faller and the surface of the earth are both moving.

 

[davidjoe]

I’m just the interested man on the street, guys, don’t judge me too harshly. I hadn’t realized Peter and PeroK weren’t the same author above, quoting me that fast, for a few minutes lol.

A true outsider’s perspective is interesting sometimes, maybe in my case concerning what is or isn’t as difficult to accept, or to grasp.

I think the YouTube sound bites by about 5-10 physicists or pop physics personas are for views yes, but also possibly an “inside baseball” pump the brakes message to academia saying hey, look where this is leading, especially in the logical extreme of this or that, subject.

Mass going to infinity, for example. Doesn’t matter how small the mass is, it goes to infinity. It receives “energy” going to infinity, to keep accelerating, and converts that energy toward infinite mass, just because it’s going faster. Common folk tend to reject infinity as part of, or the outcome of an equation. Strictly speaking, the tiniest fraction of it, is it.

Theories that support infinite universes, again, I would wonder what being observed can lead one to think there are infinite universes. 10 to the 500th power of string theories. As an outsider, one thing I don’t see is much public criticism of another’s ideas, in the field. Not saying it doesn’t happen. I’m just wondering how they get the momentum they do, such as string theory did.

 

[jbriggs444]

Mass going to infinity, for example. Doesn’t matter how small the mass is, it goes to infinity.

It does not. Mass (in the modern accepted meaning) does not increase with velocity at all. We do not use relativistic mass. We use rest mass. Also known as invariant mass. And call it "mass". See our Insight article here.

In the modern terminology, "mass" is the energy (divided by c²) of an object in a frame of reference where it is at rest.

A slightly more general definition is that the "mass" of an object is the magnitude of its energy-momentum four-vector. That is to say, $m^2 = E^2/c^4 - p^2/c^2$. For something at rest, $p=0$ and $E=mc^2$. In the case of anything moving at light speed, $E = pc$ and $m=0$.

It receives “energy” going to infinity, to keep accelerating

Yes. If mass is constant, energy increases without bound as speed increases toward $c$. The Bertozzi experiment is a good demonstration. And interesting to watch.

Common folk tend to reject infinity as part of, or the outcome of an equation. Strictly speaking, the tiniest fraction of it, is it.

Common people who have not taken a course in real analysis have a rather lacking understanding of infinite quantities.

Theories that support infinite universes...

Are not on topic in this thread.

More generally, if your mission is to kvetch about physics, you need to find some scholarly references. Or another forum.

 

[davidjoe]

Someone in free fall (and reasonably nearby) will find that the Empire State Building, foundations and all, is accelerating at 1g while they are at rest and their accelerometer is reading zero, no force because they’re free-falling. On what basis do you justify the claim that your perspective (no movement relative to you and the surface of the earth) is more “real” then the free-faller’s perspective (earth and building are moving towards them?

Before you answer, I’m going to add one more thing: the person you are trying to convince is an astronomer on Mars, sitting peacefully in their easy chair and watching through a telescope - so as far as they are concerned the free-faller and the surface of the earth are both moving.

It’s not that one is more real than the other.

Someone in free fall, in a vacuum, never stops accelerating, right? So, there is always more gravity “forcing” them to go faster, wherever they are in the fall, until they pass its source. Unlike floating in space you are being accelerated in free fall. By this, perhaps the accelerometer at highest sensitivity will never read zero. I have understood their function to follow their name.

If the Zero G airplane doesn’t keep its downward speed going, the occupants no longer experience zero G. It’s simply removing wind resistance. I could be wrong but what we call weightless, in water, free fall, or the zero G plane, is not the same as weightless where there is truly minuscule or no gravity.

 

[jbriggs444]

It’s not that one is more real than the other.

Someone in free fall, in a vacuum, never stops accelerating, right?

In the Newtonian model under constant gravity, yes. That is unrealistic. There is no such thing as an infinite constant gravity well.

The relativistic model of gravity is something else again. Someone in free fall is not accelerating at all. It is just that some choices of coordinate system accelerate upward relative to freely falling objects.

Unlike floating in space you are being accelerated in free fall. By this, perhaps the accelerometer at highest sensitivity will never read zero.

I have no idea why you think that a coordinate acceleration is detectable by a sufficiently sensitive physical accelerometer. It cannot be. Coordinates are things that are conjured with pencil and paper. They are not physical.

 

[davidjoe]

It does not. Mass (in the modern accepted meaning) does not increase with velocity at all. We do not use relativistic mass. We use rest mass. Also known as invariant mass. And call it "mass". See our Insight article here.

In the modern terminology, "mass" is the energy (divided by c²) of an object in a frame of reference where it is at rest.

A slightly more general definition is that the "mass" of an object is the magnitude of its energy-momentum four-vector. That is to say, $m^2 = E^2c^4 - p^2c^2$. In the case of anything moving at light speed, $E^2 = p^2c^2$ and $m=0$.


Yes. If mass is constant, energy increases without bound as speed increases without bound.


Common people who have not taken a course in real analysis have a rather lacking understanding of infinite quantities.

Are not on topic in this thread.

More generally, if your mission is to kvetch about physics, you need to find some scholarly references. Or another forum.

I will read that. It can’t be overstated how much I appreciate someone saying that mass does not go to infinity.

 

[PeterDonis]

I think an accelerometer does not detect force, just movement.

It detects proper acceleration, which is produced by a force. Proper acceleration is not the same thing as movement.

If I attached one to the base of the Empire State Building

It would read nonzero because the Empire State Building has nonzero proper acceleration, because it is being pushed on by the Earth's surface. Or, to put it another way, it has weight.

and then shoved on it, there’s force but no movement.

Yes, but the accelerometer, if it were sensitive enough, would detect the force you exerted as a change from the force (weight) that it was being subjected to before. And that would be the case even if the building itself did not move at all relative to you.

 

[PeterDonis]

Mass going to infinity

"Relativistic mass" is an outdated concept. If you search PF on that term you will find plenty of previous threads explaining why.

 

[PeterDonis]

Someone in free fall, in a vacuum, never stops accelerating, right?

No. Someone in free fall has zero proper acceleration.

That someone might have nonzero coordinate acceleration relative to some other object, such as the Earth (for example, the International Space Station in its free-fall orbit), but coordinate acceleration is a frame-dependent quantity, not an invariant. Proper acceleration--what an accelerometer measures--is the invariant.

 

[PeterDonis]

there is always more gravity “forcing” them to go faster

Gravity is not a force in GR.

 

[PeterDonis]

I could be wrong

You are. See below.

As an observation: an awful lot of what you think you know about physics appears to be wrong.

but what we call weightless, in water, free fall, or the zero G plane

Are already not all the same. "Weightless" floating in water is not actually weightless; an accelerometer attached to you does not read zero. Free fall, such as the International Space Station in orbit, or being in the zero G plane during the weightless part of its trajectory, are weightless; an accelerometer attached to you reads zero.

is not the same as weightless where there is truly minuscule or no gravity.

Wrong. Free fall/zero G plane are the same "weightless" (accelerometer reads zero) as "where there is truly miniscule or no gravity".

 

[Drakkith]

A true outsider’s perspective is interesting sometimes, maybe in my case concerning what is or isn’t as difficult to accept, or to grasp.

Don't take this the wrong way, as I'm not trying to insult you, but we get people like you every day here at PF. Our goal is literally to help people who don't understand science (you and 99% of everyone who comes to PF) learn about science. Most of us long-time members are well aware of what is and isn't easy to grasp in various subjects.

I think the YouTube sound bites by about 5-10 physicists or pop physics personas are for views yes, but also possibly an “inside baseball” pump the brakes message to academia saying hey, look where this is leading, especially in the logical extreme of this or that, subject.

Not really. These kinds of videos or sound bites are for keeping the public up to speed in what is happening in various fields, generating general interest in science, and possibly many other reasons. But I don't think that anyone is seriously trying to send 'academia' or other scientists a message using them. There are plenty of other ways to do that, like conferences, lectures, professional meetings, publications, etc.

Theories that support infinite universes, again, I would wonder what being observed can lead one to think there are infinite universes. 10 to the 500th power of string theories. As an outsider, one thing I don’t see is much public criticism of another’s ideas, in the field. Not saying it doesn’t happen. I’m just wondering how they get the momentum they do, such as string theory did.

Criticism outside of professional avenues is generally something to be avoided, as it tends to be viewed as petty and unprofessional. Besides, a good critique of a field generally requires advanced knowledge and explanation using math and everything else to show that the critique is valid. This doesn't lend itself well to podcasts, videos, or other avenues of talking to the public since the public wouldn't understand any of it anyways unless it is vastly simplified. And if it's vastly simplified then it isn't useful to the person(s) being critiqued. They're better off just reading the full article critiquing them and responding in kind.