[Gulliver]

There's a recurring theme of ignorance in the upper forums regarding Newton's Laws of Motion. His first major work, Philosophia naturalis principia mathematica, describes three fundamental laws of motion. The concept that FEer seem to struggle to handle and properly apply is acceleration. Even TheEngineer used to argue that acceleration was relative. It is not. Location is relative since there is no intrinsic coordinate system. Velocity is relative. In the thought experiment with two ships, altogether alone in the Universe, passing each other, observers on each ship can't determine which ship is in motion.

However, you know whether you're accelerating. You feel the force involved. You feel your weight on Earth. You fell the merry-go-round pulling you towards its center. You feel the airplane turning, rising, or dropping. So the argument that planes just "fly around" to delay their arrival fails quickly: The passengers would feel (and see) the turns and bust the required conspiracy.

Another problem FEers tend to have is trying to bash noobs with the circumnavigation argument. FEers argue that you can travel "around" the Earth, say on the Equator by traveling due east. Yes, on the FE that's a curved path, but you'd travel a curved path if you flew due east on the RE too. This fails: the passengers can detect the curved path. The pilot must steer the rudder to maintain the curved path. They would break the conspiracy. (Oh, and no, it's not a curved path on the RE, ignored changing in altitude. One needs only remember that a straight line on the surface of sphere follows the surface, just like the plane would. Indeed on an RE, the pilots and passenger would not feel any "curvature".)

One more lesson for this post: the term acceleration should be used carefully, in its scientific context. For example, to Thorks's slow acceptance, you can travel away from something, yet accelerate towards it. The ISS, for example, accelerates toward the gravitational center of the RE but never travels towards it. To Tom Bishop's chagrin, acceleration is the change in velocity, in speed, direction, or both. It does not mean going fast (or slow).

[Thork]

There's a recurring theme of ignorance in the upper forums regarding Newton's Laws of Motion. His first major work, Philosophia naturalis principia mathematica, describes three fundamental laws of motion. The concept that FEer seem to struggle to handle and properly apply is acceleration. Even TheEngineer used to argue that acceleration was relative. It is not. Location is relative since there is no intrinsic coordinate system. Velocity is relative. In the thought experiment with two ships, altogether alone in the Universe, passing each other, observers on each ship can't determine which ship is in motion.

You are aware that most of Newton's work was actually related to alchemy and that you are just picking and choosing the things you like from his studies? And then you start talking about relativity. Newton was not the founder of those theories.

However, you know whether you're accelerating. You feel the force involved. You feel your weight on Earth. You fell the merry-go-round pulling you towards its center. You feel the airplane turning, rising, or dropping. So the argument that planes just "fly around" to delay their arrival fails quickly: The passengers would feel (and see) the turns and bust the required conspiracy.

No, they wouldn't. When you train as a pilot, one fun lesson involves a blindfold. Your instructor will pull you all over the sky, and ask you to recover. The really good instructors can make you feel like you are descending when you are actually upside down and climbing. Please do some research before stating 'facts'. Your misinformation makes our forum look like an argument over a beer, not a fascinating homage to science.
https://en.wikipedia.org/wiki/The_leans
^ Read that to understand why a passenger and even pilot have no idea from forces what their body is doing. Its one of the first things pilots learn, because if they don't trust their instruments over their senses, it is often fatal.

Another problem FEers tend to have is trying to bash noobs with the circumnavigation argument. FEers argue that you can travel "around" the Earth, say on the Equator by traveling due east. Yes, on the FE that's a curved path, but you'd travel a curved path if you flew due east on the RE too. This fails: the passengers can detect the curved path. The pilot must steer the rudder to maintain the curved path. They would break the conspiracy. (Oh, and no, it's not a curved path on the RE, ignored changing in altitude. One needs only remember that a straight line on the surface of sphere follows the surface, just like the plane would. Indeed on an RE, the pilots and passenger would not feel any "curvature".)

Are you suggesting that passengers would feel rudder (you don't turn with rudder, you yaw ... but anyway) to make a correction of 24859/360 = roughly one degree heading change every 70 miles?
You would only need to set a bank angle of roughly 0.06 degrees at 550 mph. 0.06 degrees is absolutely imperceptible. With wind and turbulence a pilot would not have a clue they were doing this.

One more lesson for this post: the term acceleration should be used carefully, in its scientific context.

Lesson? You've been wrong about absolutely everything so far.

For example, to Thorks's slow acceptance, you can travel away from something, yet accelerate towards it. The ISS, for example, accelerates toward the gravitational center of the RE but never travels towards it.

The ISS doesn't accelerate. Its in low earth orbit at a constant speed of around 17000mph To have a force of acceleration in one direction and an opposing force that cancels that out in the opposite direction does not mean one is accelerating. If I get in my car and accelerate to 150mph before the wind resistance is so great my car stops accelerating doesn't mean I am still accelerating. It means I am now at 150mph and that is that as the forces balanced.
You are confusing angular velocity with angular acceleration.
https://en.wikipedia.org/wiki/Angular_velocity

I find it hard to understand from my tens of thousands of posts that you would pick one from your example, and its one where you don't get it. not one where I have been wrong. I mean I must have been wrong at some point in that time, so how did you end up with that example?

[Gulliver]

Let's start slow. You seem to again need help with basic grade-school physics. Let's consider here:

The ISS doesn't accelerate. Its[sic] in low earth orbit at a constant speed of around 17000mph.

Please recall your grade school physics. Acceleration is a change in magnitude, direction, or both of an object's velocity. Your point about a constant speed (magnitude) is not sufficient to support your claim that "t]he ISS doesn't accelerate." The ISS's velocity changes direction constantly, so the ISS constantly accelerates. Once you understand this, let me know and we can consider your other points. Just to check your proper understanding, ask yourself in what direction does the ISS accelerate and why? Thanks!

[Thork]

The ISS's velocity changes direction constantly, so the ISS constantly accelerates.

No, ClockTower, it doesn't.

https://en.wikipedia.org/wiki/Angular_velocity

[Gulliver]

The ISS's velocity changes direction constantly, so the ISS constantly accelerates.

No, ClockTower, it doesn't.

https://en.wikipedia.org/wiki/Angular_velocity

Please tell me then what the ISS's velocity was at 0 UTC and 1 UTC this morning. You argue that the velocity was the same, right? Why didn't the ISS leave orbit then? Why didn't the mutual attraction between the ISS and the RE cause the ISS to fall towards their center of gravity?

[Thork]

Because it has an angular velocity.

It doesn't need to be accelerating to change direction constantly.

https://en.wikipedia.org/wiki/Angular_acceleration
is something else entirely. The ISS is not accelerating. This is why its speed and angular displacement remain constant.

[Gulliver]

Because it has an angular velocity.

It doesn't need to be accelerating to change direction constantly.

https://en.wikipedia.org/wiki/Angular_acceleration
is something else entirely. The ISS is not accelerating. This is why its speed and angular displacement remain constant.

Did you really just post that an object need not accelerate to change direction? Amazing!

You can convince me of your point in two ways: 1) Provide a reference that says something with angular velocity cannot accelerate linearly. or 2) Explain how the ISS stays in orbit without being accelerated constantly towards the RE. Spoiler alert: I've seen you lose this point in the archives in the old site. I laughed reading it weeks ago and did not expect to get a second round of laughs today. Thanks!

[jroa]

I thought Newton's physics were proven wrong more than one hundred years ago?  It is still taught in school because of its child like simplicity. 

[Rama Set]

Jroa, if you knew that, then you would also know that Newton's physics are incredibly accurate at almost all scales. They are much simpler than QM and Einsteinian relativity, so they are still an incredibly valuable and accurate tool.

[Thork]

Because it has an angular velocity.

It doesn't need to be accelerating to change direction constantly.

https://en.wikipedia.org/wiki/Angular_acceleration
is something else entirely. The ISS is not accelerating. This is why its speed and angular displacement remain constant.

Did you really just post that an object need not accelerate to change direction? Amazing!

You can convince me of your point in two ways: 1) Provide a reference that says something with angular velocity cannot accelerate linearly. or 2) Explain how the ISS stays in orbit without being accelerated constantly towards the RE. Spoiler alert: I've seen you lose this point in the archives in the old site. I laughed reading it weeks ago and did not expect to get a second round of laughs today. Thanks!

1) I didn't say it had to. But acceleration is a rate of change. Velocity is not.
2) No, I got bored of the debate last time as I am becoming now, because the people I was debating with weren't very good at physics. I already explained how a constant force of acceleration does not necessarily yield constant acceleration of the body in question using the car/wind resistance argument. The ISS is not constantly accelerating. It is in a stable orbit (assuming orbit exists - but another argument for another day) by virtue of all those forces being balanced. If it was accelerating it would either speed up or fail to remain in its orbit. It has a constant angular velocity.

[inquisitive]

I drive at 30mph round a corner.   Am I accelerating?

[Thork]

I drive at 30mph round a corner.   Am I accelerating?

Assuming you are already in the corner at 30mph and you have no intention of every turning out of it (like a satellite) then no.

[Gulliver]

Because it has an angular velocity.

It doesn't need to be accelerating to change direction constantly.

https://en.wikipedia.org/wiki/Angular_acceleration
is something else entirely. The ISS is not accelerating. This is why its speed and angular displacement remain constant.

Did you really just post that an object need not accelerate to change direction? Amazing!

You can convince me of your point in two ways: 1) Provide a reference that says something with angular velocity cannot accelerate linearly. or 2) Explain how the ISS stays in orbit without being accelerated constantly towards the RE. Spoiler alert: I've seen you lose this point in the archives in the old site. I laughed reading it weeks ago and did not expect to get a second round of laughs today. Thanks!

1) I didn't say it had to. But acceleration is a rate of change. Velocity is not.
2) No, I got bored of the debate last time as I am becoming now, because the people I was debating with weren't very good at physics. I already explained how a constant force of acceleration does not necessarily yield constant acceleration of the body in question using the car/wind resistance argument. The ISS is not constantly accelerating. It is in a stable orbit (assuming orbit exists - but another argument for another day) by virtue of all those forces being balanced. If it was accelerating it would either speed up or fail to remain in its orbit. It has a constant angular velocity.

So is the ISS constantly changing the direction of its motion? Isn't changing direction of motion one form of acceleration?

[Gulliver]

I drive at 30mph round a corner.   Am I accelerating?

Assuming you are already in the corner at 30mph and you have no intention of every turning out of it (like a satellite) then no.

Where does the intent of an object come into the definition of acceleration? (BTW great point, inquisitive!)

[inquisitive]

I drive at 30mph round a corner.   Am I accelerating?

Assuming you are already in the corner at 30mph and you have no intention of every turning out of it (like a satellite) then no.

How would you calculate acceleration?  Knowing the units are m/s/s (in metric).  And the formula v^2 = u^2 + 2as.

[Thork]

Because it has an angular velocity.

It doesn't need to be accelerating to change direction constantly.

https://en.wikipedia.org/wiki/Angular_acceleration
is something else entirely. The ISS is not accelerating. This is why its speed and angular displacement remain constant.

Did you really just post that an object need not accelerate to change direction? Amazing!

You can convince me of your point in two ways: 1) Provide a reference that says something with angular velocity cannot accelerate linearly. or 2) Explain how the ISS stays in orbit without being accelerated constantly towards the RE. Spoiler alert: I've seen you lose this point in the archives in the old site. I laughed reading it weeks ago and did not expect to get a second round of laughs today. Thanks!

1) I didn't say it had to. But acceleration is a rate of change. Velocity is not.
2) No, I got bored of the debate last time as I am becoming now, because the people I was debating with weren't very good at physics. I already explained how a constant force of acceleration does not necessarily yield constant acceleration of the body in question using the car/wind resistance argument. The ISS is not constantly accelerating. It is in a stable orbit (assuming orbit exists - but another argument for another day) by virtue of all those forces being balanced. If it was accelerating it would either speed up or fail to remain in its orbit. It has a constant angular velocity.

So is the ISS constantly changing the direction of its motion? Isn't changing direction of motion one form of acceleration?

ffs. angular velocity. What is wrong with you?

[spaceman spiff]

Wait, so an obect in circular motion with constant angular speed is not accelerating? Is this what Thork is saying? Wow...

[garygreen]

The ISS doesn't accelerate.

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

Angular acceleration is the rate of change of angular velocity.

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

In physics, the angular velocity is defined as the rate of change of angular displacement and is a vector quantity (more precisely, a pseudovector) which specifies the angular speed (rotational speed) of an object and the axis about which the object is rotating.

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

Acceleration, in physics, is the rate at which the velocity of an object changes over time.

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

Velocity is the rate of change of the position of an object, equivalent to a specification of its speed and direction of motion, e.g. 60 km/h to the north[...]Velocity is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value (magnitude) of velocity is called "speed"[...]

The ISS has a velocity (magnitude and direction).  It's velocity vector changes due to the force of gravity.  This change caused by the force of gravity is known as acceleration.

More info: https://www.khanacademy.org/science/physics/newton-gravitation/gravity-newtonian/v/acceleration-due-to-gravity-at-the-space-station

Seriously, take one physics class if you want to argue about physics.

[Thork]

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

Angular acceleration is the rate of change of angular velocity.

This is what I have been trying to say. If angular velocity remains the same (as in a stable orbit), then there is no rate of change hence no acceleration.

This seems like a very easy topic for you to grasp.

[spaceman spiff]

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

Angular acceleration is the rate of change of angular velocity.

This is what I have been trying to say. If angular velocity remains the same (as in a stable orbit), then there is no rate of change hence no acceleration.

This seems like a very easy topic for you to grasp.

Nice job cherry picking garygreen's post. You can say that there's no angular acceleration, but not that there's no acceleration. From garygreen's post:

Acceleration, in physics, is the rate at which the velocity of an object changes over time.

Velocity is the rate of change of the position of an object, equivalent to a specification of its speed and direction of motion, e.g. 60 km/h to the north[...]Velocity is a vector physical quantity; both magnitude and direction are required to define it. The scalar absolute value (magnitude) of velocity is called "speed"[...]

Since the velocity vector of the ISS changes direction, it is therefore accelerating