[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.

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

I am saying that the ISS is not accelerating.

I am sat in my chair. Under RET that means I have a force of acceleration towards the ground at 9.81 m/s^2.
But I'M NOT ACCELERATING ANYWHERE. At t=0 I am sat in my chair and at t=5 minutes I'm still in the exact same spot. There has been no rate of change at all.  Having a force of acceleration applied to me doesn't mean I am accelerating. The forces are cancelled. I'm stationary. The ISS has its forces cancelled. It travels with a constant angular velocity. Its not accelerating anywhere.

I got bored of this the last time. I'm getting bored again. Feel free to say how I was completely wrong about everything again next time you want to try to discredit me. Somehow my running out of patience over simple concepts is deemed as my not understanding something. But to me it just proves what a bunch of disingenuous little trolls you are.

[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

I am saying that the ISS is not accelerating.

I am sat in my chair. Under RET that means I have a force of acceleration towards the ground at 9.81 m/s^2.
But I'M NOT ACCELERATING ANYWHERE. At t=0 I am sat in my chair and at t=5 minutes I'm still in the exact same spot. There has been no rate of change at all.  Having a force of acceleration applied to me doesn't mean I am accelerating. The forces are cancelled. I'm stationary. The ISS has its forces cancelled. It travels with a constant angular velocity. Its not accelerating anywhere.

I got bored of this the last time. I'm getting bored again. Feel free to say how I was completely wrong about everything again next time you want to try to discredit me. Somehow my running out of patience over simple concepts is deemed as my not understanding something. But to me it just proves what a bunch of disingenuous little trolls you are.

I didn't even mention forces in my post, but whatever. Just to make sure we are in the same page, please define acceleration. I feel like we are not agreeing on the basics.
As a side note, what other force is acting on the ISS besides gravity?

[Thork]

How about you read the thread then, and not jump in at the end shouting the odds?

[garygreen]

I am saying that the ISS is not accelerating.

I think you're just confusing speed and velocity.  Speed is a scalar quantity.  It is described only by magnitude.  The speed of the ISS is constant.

Velocity is a vector quantity.  It is always described by magnitude and direction.  The direction component of the ISS' velocity changes as it orbits due to the force of gravity.  This is acceleration.  Any change in an objects' velocity is acceleration.

I am sat in my chair. Under RET that means I have a force of acceleration towards the ground at 9.81 m/s^2.
But I'M NOT ACCELERATING ANYWHERE. At t=0 I am sat in my chair and at t=5 minutes I'm still in the exact same spot. There has been no rate of change at all.  Having a force of acceleration applied to me doesn't mean I am accelerating. The forces are cancelled. I'm stationary. The ISS has its forces cancelled. It travels with a constant angular velocity. Its not accelerating anywhere.

The ISS is not resting on a chair resting on the Earth's surface.  The force of gravity is not cancelled out by anything.  That's what we're trying to tell you.  It's always freely falling toward the Earth because of the force of gravity.  This force is not cancelled out.  It changes the direction of the ISS' velocity vector.  That's acceleration.

The ISS doesn't stay in orbit because the force of gravity is cancelled out.  The force of gravity acts on the ISS and causes it to accelerate in the direction of the Earth's surface. 



Look at how the velocity vector is constantly changing direction.

http://en.wikipedia.org/wiki/Orbit#Understanding_orbits

There are a few common ways of understanding orbits:

-As the object moves sideways, it falls toward the central body. However, it moves so quickly that the central body will curve away beneath it.

-A force, such as gravity, pulls the object into a curved path as it attempts to fly off in a straight line.

-As the object moves sideways (tangentially), it falls toward the central body. However, it has enough tangential velocity to miss the orbited object, and will continue falling indefinitely. This understanding is particularly useful for mathematical analysis, because the object's motion can be described as the sum of the three one-dimensional coordinates oscillating around a gravitational center.

Notice that all of these descriptions involve acceleration due to gravity.  Gravity alters the velocity vector.  That's what acceleration is.

[Thork]

Christ on a bike. I know their is an acceleration due to gravity in the RET model. I also know that angular acceleration is a vector quantity and not a scalar. BUT THE ISS IS NOT ACCELERATING! It has an angular velocity. Not an angular acceleration. Why are you being so obtuse?

[garygreen]

BUT THE ISS IS NOT ACCELERATING! It has an angular velocity.

These two sentences cannot both be true.

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

angular velocity is defined as the rate of change of angular displacement

Angular velocity is the rate at which the direction component of a velocity vector changes over time.  Acceleration is the rate at which a velocity vector changes over time.  Angular velocity requires acceleration.

Exactly what we've been trying to tell you from the beginning is that the ISS could not have any angular velocity without a force causing it to accelerate in the direction of the Earth's surface.  Angular velocity is a quantity that describes how much its velocity vector changes over time.

[garygreen]

Or consider the following reductio:

Let's assume that you're correct that the ISS is not accelerating.  That means, by definition, that its velocity vector does not change.  So, if the ISS is above the Earth with some velocity, and if that velocity does not change, then, per Newton's 1st, it will move at a constant speed and direction until some force acts on it.  The trajectory of the ISS would look like this:



It would have to.  If the velocity vector doesn't change, then the path of the ISS will always be a straight line in the direction of its velocity.

Since its path is elliptical and not a straight line, its velocity must change.  Any change in velocity over time is acceleration.

[Thork]

Exactly what we've been trying to tell you from the beginning is that the ISS could not have any angular velocity without a force causing it to accelerate in the direction of the Earth's surface.  Angular velocity is a quantity that describes how much its velocity vector changes over time.

I am not disputing that there is a component of acceleration. I'm saying the ISS itself is not accelerating. The forces balance.
Read the bloody thread.

[inquisitive]

Some numbers please.

[Thork]

Some numbers please.

4, 303, 42, 232, 2.

Numbers of what?

[inquisitive]

Some numbers please.

4, 303, 42, 232, 2.

Numbers of what?

What is the acceleration of the ISS?

[spaceman spiff]

Exactly what we've been trying to tell you from the beginning is that the ISS could not have any angular velocity without a force causing it to accelerate in the direction of the Earth's surface.  Angular velocity is a quantity that describes how much its velocity vector changes over time.

I am not disputing that there is a component of acceleration. I'm saying the ISS itself is not accelerating. The forces balance.
Read the bloody thread.

Which forces? Gravity and...? Also, if there's a non-zero component of the acceleration (as you may have implied by "there is a component of acceleration"), it means that the ISS is accelerating.

[Thork]

Some numbers please.

4, 303, 42, 232, 2.

Numbers of what?

What is the acceleration of the ISS?

0.

[garygreen]

I am not disputing that there is a component of acceleration. I'm saying the ISS itself is not accelerating. The forces balance.
Read the bloody thread.

That doesn't make sense.  Please clarify.  The ISS can't be accelerating and not accelerating.

I think the problem is that you're using 'acceleration' and 'angular acceleration' interchangeably.  They don't mean the same thing.  Angular acceleration is a change in angular velocity.  Acceleration is a change in any velocity vector.  Speaking of reading the thread, this entire discussion could have been avoided by you reading my first post in this thread that contains these definitions. 

The ISS has a constant angular velocity (no angular acceleration).  It does not have a constant velocity.  Those are different things.  Its speed is constant.  Its velocity is not.  This is because the ISS is being accelerated by the force of gravity in the direction of the Earth's surface, as per all of the sources I've cited.  This is the very definition of an orbit.  It couldn't stay in orbit without being accelerated toward the surface of the Earth.

The OP was exactly right, and you basically just proved his point with your posts in this thread.  You just don't have any concept that acceleration means a specific thing and has a specific definition.  It doesn't just mean 'going faster.'  And it means something different from angular acceleration.  Just as angular velocity means something different than velocity.  You're just mixing up all these terms and definitions and then acting like everyone else is an idiot for not knowing that you're doing that.

[Thork]

I can't be any more specific. I'm sat in my chair. I'm not accelerating anywhere. t=0 is the same as t=15 seconds.
There is a force of acceleration exerted on me, But I'M NOT ACCELERATING.

[garygreen]

I can't be any more specific.

You could start by using the correct words to describe the correct things.

I'm sat in my chair. I'm not accelerating anywhere. t=0 is the same as t=15 seconds.
There is a force of acceleration exerted on me, But I'M NOT ACCELERATING.

You experience no acceleration in the direction of the Earth's surface because you are resting on a chair.  The force of the chair opposes equally the force of gravity.  The ISS is not resting on a chair.  There is no force opposing the force of gravity for the ISS.  Again, if there were, then the ISS could not be in orbit.  I don't think you actually read my posts.  I've explained this like five times now.  You're just like PP.  You just read a couple of sentences and skip over responding to the substance of what anyone says.  Just hit reply and start typing something.  And you think for some reason that it's a mark of intelligence.  You're fucking weird.

There isn't a legitimately licensed pilot on the planet who could possibly have this kind of trouble applying and speaking intelligently about Newton's laws.  Get out with that nonsense.  What a joke. 

e: you also don't seem to get what an inertial frame of reference is, which would also be super troubling if you were actually a licensed pilot.  You are not accelerating toward the surface of the Earth when seated (or accelerating at all in your local, rotating inertial frame.  Everything around you is moving at the same rate under the same forces).  But, you are being accelerated in a non-rotating inertial frame (say, from the point of view of someone looking at the whole Earth from a stationary position in space).  Your velocity vector changes as you rotate around the globe on the Earth's surface.  Just as with the ISS, if it didn't, then you would travel at a constant speed and direction and fly off the surface as it fell away below you.

Any change in the direction or magnitude of a velocity vector is called acceleration.  By definition.  That's what the word means.

[Gulliver]

I can't be any more specific. I'm sat in my chair. I'm not accelerating anywhere. t=0 is the same as t=15 seconds.
There is a force of acceleration exerted on me, But I'M NOT ACCELERATING.

How about answer the simple question:

Is the ISS's velocity (note: not asking about angular velocity) changing direction at any point in its orbit? Thanks.

[Thork]

There is no force opposing the force of gravity for the ISS.

Ok, great. Now I know why you are having so much trouble with your basic physics. You don't know what centripetal force is.



Cool. Go look it up, and come back a better debater. I'm gonna call time on this debate. its really dull and has nothing to do with earth's shape. Til next time ... Thork out.

[Gulliver]

There is no force opposing the force of gravity for the ISS.

Ok, great. Now I know why you are having so much trouble with your basic physics. You don't know what centripetal force is.



Cool. Go look it up, and come back a better debater. I'm gonna call time on this debate. its really dull and has nothing to do with earth's shape. Til next time ... Thork out.

Would you do that diagram again please, this time with only real forces? Thanks! Reference: https://answers.yahoo.com/question/index?qid=20100619084420AAl0nDP

[Thork]

lol. yahoo answers. My source was http://hyperphysics.phy-astr.gsu.edu/hbase/orbv.html

note the .edu
An educational website. Not a bunch of dumb teens unqualified to answer the questions asked.