Silly question?

[danielj]

17 hours ago, studiot said:

That's really good news. I think we can build on this mechanical experience.

I have been busy these last week but I see other members have been looking after you.

I would, however like to bring your feet fimly back to ground to feel the gravity.

I think you could benefit from this book. It is one of a kind where the author tries to use physics to explain well known mathematics, rather than the other way round.

So rather than dry mathematical general theorems about polygons try the polygon of least area (p35)

The Mathematical Mechanic  :  Mark Levi :  Princeton University Press.

 

But remember to keep asking questions as you will find much unfamiliar as well as some familiar stuff.

 

Thank you, much appreciated

On 2/15/2025 at 3:49 PM, Genady said:

The measurement by an accelerating observer and by a non-accelerating observer will be different.

I’m just trying visualise some of the mechanics of this, so would it also be true to say that if I (tried) to take a ‘snap-shot’ measurement, with any combination of inertial/accelerating reference frames that in reality there is no way to take a snap-shot, as what was the time frame of the snap shot (by that phrase I mean a static measurement) and no matter how small the time frame, change will have occurred in one or more dimensions?

The questions should  get less stupid as I progress, but I can’t promise 

5 hours ago, KJW said:

The Equivalence Principle basically says that over distances that are sufficiently small for the tidal effect to be negligible, being in a gravitational field is indistinguishable from being in an accelerated frame of reference. This is illustrated by the following diagram:
 

 

However, over larger distances, the gravitational field does differ from being in an accelerated frame of reference due to the tidal effect, which is a manifestation of spacetime curvature that is absence from being in an accelerated frame of reference in flat spacetime.

 

 

What I said about perception of the vertical direction was not about skewing reality, but a consequence of the equivalence principle. I personally discovered the perception of the vertical direction when I was a teenager in an amusement park ride called the "Rotor". I noticed that the people directly opposite me before the start of the ride were very much above me during the ride. I immediately realised that what we regard as up or down is actually a perception that we don't normally notice unless we are in an environment that challenges the notion of up or down.

 

 

So they were above you if you used the ground as your reference frame, but not if you used the rotor itself? Your brain used the ground? 

reading this back I see there being potentially many different frames of reference, equally valid?

Edited Sunday at 04:59 PM by danielj

[Genady]

26 minutes ago, danielj said:

I’m just trying visualise some of the mechanics of this, so would it also be true to say that if I (tried) to take a ‘snap-shot’ measurement, with any combination of inertial/accelerating reference frames that in reality there is no way to take a snap-shot, as what was the time frame of the snap shot (by that phrase I mean a static measurement) and no matter how small the time frame, change will have occurred in one or more dimensions?

You can take a snapshot of an accelerometer that you hold in your hand. It will show if you accelerate or not.

[danielj]

23 minutes ago, Genady said:

You can take a snapshot of an accelerometer that you hold in your hand. It will show if you accelerate or not.

I see, yes. Thank you. 
I get caught in the details, not always helpful to me. 

[KJW]

2 hours ago, danielj said:

So they were above you if you used the ground as your reference frame, but not if you used the rotor itself? Your brain used the ground? 

Before the ride starts, the people opposite me are at the same height above the ground as I am. During the ride, this doesn't change as the rotation axis of the ride is fixed. But due to the vector addition of the centrifugal acceleration and the earth's gravitational field, my perception of the vertical is no longer the same as the "true" vertical. The people opposite me appear to be well above me even though they remain the same height above the ground as I am. Because the centrifugal acceleration of the ride is about 3g, the perceived vertical direction is about 20° above the horizontal.

 

 

2 hours ago, danielj said:

reading this back I see there being potentially many different frames of reference, equally valid?

Yes, all frames of reference are equally valid in general relativity.

 

 

[danielj]

27 minutes ago, KJW said:

Before the ride starts, the people opposite me are at the same height above the ground as I am. During the ride, this doesn't change as the rotation axis of the ride is fixed. But due to the vector addition of the centrifugal acceleration and the earth's gravitational field, my perception of the vertical is no longer the same as the "true" vertical. The people opposite me appear to be well above me even though they remain the same height above the ground as I am. Because the centrifugal acceleration of the ride is about 3g, the perceived vertical direction is about 20° above the horizontal.

 

 

Yes, all frames of reference are equally valid in general relativity.

 

 

 My take away from this is that I am lacking logical thinking skills, when it comes to physics. In that, I can’t make assumptions and expect to get the right answer. Understanding the question is more important than the answer I think.

thank you

[Phi for All]

20 hours ago, danielj said:

 My take away from this is that I am lacking logical thinking skills, when it comes to physics. In that, I can’t make assumptions and expect to get the right answer. Understanding the question is more important than the answer I think.

thank you

You aren't supposed to be using logic. Those are formal rules used in philosophy and maths.

What you're thinking of is reasoning skills, or critical thinking skills. Those are what we all need to get better at.

Unfortunately, I think what you're referring to is something completely different. What you're "taking away" from this is that your assumptions are based on your intuition, and science has no obligation to make any kind of intuitive sense. There are plenty of explanations that seem at odds with what we think we know. Time is certainly not intuitive, and the laws of physics don't recognize a difference between past and future. And is there anything intuitive about the Placebo Effect? Or Black Holes?

Also, "right answer" is not a scientific concept. Best supported explanations for various phenomena is how theory works. 

[danielj]

5 hours ago, Phi for All said:

and the laws of physics don't recognize a difference between past and future.

Thank you, thats all very helpful. Would you mind expanding the above statement please?

 

Cosmological Principle? 
 at sufficiently large scales, the universe appears as homogeneous and isotropic 

Copied from Mordreds thread ‘Cosmological Principle’

there I go with a guess again 🫣

[studiot]

Just now, danielj said:

Thank you, thats all very helpful. Would you mind expanding the above statement please?

The point about equations is that it does not matter which way round you write them.

If A = B  then   B  = A

 

Most of the laws of Physics are of this form so if Time is involved it does not matter whether time goes forward or backwards, the equations still hold.

 

There is one major law of Physics called the second law of thermodynamics which doe not have the form of an equality (or equation), it is an inequality so

 

If A < B  then going the other way B is greater than A.

Since the second law involves time it cannot be reversed and hold the same form like an equation.