Denspressure vs Reality

Quote from: MicroBeta on November 27, 2017, 07:58:52 AM

I'm trying to understand.  You're saying we have an applied force without an acceleration and that force is the mass of the object?  In denpressure F=m?

No I'm not.
You cannot get to a constant speed without acceleration.

I still do not understand you.  Below it your post that I’m having trouble with. 

I’m saying that without acceleration and object’s speed cannot change.  Your post states “the applied force is the mass of the vehicle”.  What is unclear is how a mass can exert a force to stop an object without acceleration. 

In terms of slowing down the applied force is the mass of the vehicle. There is no acceleration.

Note that I’m using acceleration as signed quantity.  It’s either positive or negative (± acceleration). 

Mike

Quote from: Badxtoss on November 27, 2017, 09:39:08 AM

Quote from: sceptimatic on November 27, 2017, 06:05:52 AM

Quote from: defender_of_truth on November 27, 2017, 06:03:59 AM

That's literally the definition of constant deceleration. The speed changes by the same amount in each unit of time.

There's no change in constant. Constant is without change.

Can I not be constantly in motion?

Yep.

Yet I am always changing if I am in motion so can it be a constant?
If so than why can't there be a constant RATE of acceleration?

I think what you're trying to say is, if the motor and pulley pull on the rope at a constant speed and then somehow has a power surge for half a second just as that rope is cut.

If that happens then we have the springboard effect. The rope would yank and the lift would accelerate on that immediate yank only before the rope snaps but then decelerate for a small portion of that half second before simply stopping dead and accelerating back down.

I think this answers my question. So, if I'm reading this right, then the amount of deceleration is down to how long the object in question has been accelerating for, rather than just how fast it's going? So an object that accelerates for one second to reach the same speed as an object that's been accelerating for an hour, is going to decelerate for less time before coming to a dead stop? That makes sense in line with everything else you've said, I just wasn't sure.

And if that's right, I think my last question is on what happens when the platform in question decelerates. Say, the lift in question decelerates when the rope's cut; it's losing power not at a constant speed, but it has no upwards acceleration, so would that cause a dead stop too?

Let’s make this simple with a table:

Time Vel  Acc
0       0    1
1       1    1
2       2    1
3       3    1
4       4    1
5       5    1
6       6    1
7       7    1
8       8    1
9       9    1
10     10  1

From time 0 to 10 the acceleration is always 1. It is constant.

The rate of change can itself be constant over a period of time.

No, that is an equation, not a formula.  Are you sure you studied physics?

The distinction between formula and equation would be math, not physics.
Also, last time I checked, formulas often are equations. What you have objected to is both.
So have you studied anything?

Quote from: Jonny B Smart on November 26, 2017, 05:02:43 PM

1. I have launched model rockets and watched them continue to fly up after the engine burns out, so I know that Scepti is wrong from personal observations. (I’ve also tossed many balls into the air. Try it—it’s fun!)

Given everything he's said about acceleration I sincerely doubt that qualifies as an argument.

Given what he has said about rockets, it would qualify.

Either he is wrong, and rockets do accelerate rather than maintain constant speed, or he is wrong and you can continue moving after a period of constant speed. Or he is wrong on both accounts.

I disagree.
Acceleration can never be constant because of the nature of what it means. To advance in speed at every moment, or to CHANGE in speed at every moment, which means it is not a constant.

Notice how you are ignoring what acceleration is and instead focusing on speed?
Yes, a constant acceleration will result in a change in speed. So what? That doesn't mean that it can't be constant.
Consider a constant speed or constant velocity. That means you are continually changing your position. Does that mean it can't be constant? No.

A constant acceleration means your acceleration is constant. That is your change in speed is constant.

Of course you can slow down but you can never decelerate.

What is the difference?
Are you saying if you try and slow down you drop that speed instantly?

Rocket fuel is part of the mass and that burning mass does reduce the mass of the rocket.
However, the rocket is always at full thrust and that full thrust ensures the ejected burning mass matches the mass of the rocket to atmospheric push, so you're always getting a thrust to mass ratio that keeps the rocket at a constant velocity.

No you aren't.
The thrust the remains the same while the mass changes.
That means the thrust to mass ratio changes.

The only way to accelerate that rocket at full thrust would be to lose some of the rocket with each inch (for the sake of it) it moves vertically.

Such as what it does by burning the fuel.

Dumping the burning mass of fuel will keep the mass of rocket constant.

No it doesn't.
The fuel is being accelerated with the rocket until it is burnt and dumped and thus it constitutes part of the mass of the rocket.

Yes but that energy has to release from the rocket with fuel or as it (in terms of a bottle rocket or whatever).

Why can't it release as burnt fuel?

There's no such thing as throttling back on a rocket engine unless you are doing horizontal flight or water/ground based rocket propulsion.

That depends upon the engine. Lots are capable of throttling down.

Vertical flight requires no throttling down and would be absolutely counterproductive to the rocket flight.

And that is beside the point. The simple fact is you can do that.

The thrust always has to be greater than the mass of the rocket to move it.

Not the mass, the weight.

The thrusting fuel will always be at maximum.

And if this maximum is above the weight guess what? That means it continues to accelerate.

Now scepti, a nice simple one point for you:

You admit that you can have constant speed/velocity.
You claim that you can't have something constant when you have a change.
But speed/velocity is change in position per unit time.
If I start at your position and move with a constant velocity of 10 m/s, then after 1 second I am 10 m away from you, after 2 seconds I am 20 m away from you and so on.

So how can I have a constant velocity when my position is changing? It seems like according to you, the only constant velocity would be when your position doesn't change, and thus you have no velocity.

Quote from: sceptimatic on November 27, 2017, 08:17:38 AM

Quote from: MicroBeta on November 27, 2017, 07:58:52 AM

I'm trying to understand.  You're saying we have an applied force without an acceleration and that force is the mass of the object?  In denpressure F=m?

No I'm not.
You cannot get to a constant speed without acceleration.

I still do not understand you.  Below it your post that I’m having trouble with. 

I’m saying that without acceleration and object’s speed cannot change.  Your post states “the applied force is the mass of the vehicle”.  What is unclear is how a mass can exert a force to stop an object without acceleration. 

Quote from: sceptimatic on November 27, 2017, 07:17:21 AM

In terms of slowing down the applied force is the mass of the vehicle. There is no acceleration.

Note that I’m using acceleration as signed quantity.  It’s either positive or negative (± acceleration). 

Mike

What do you mean by positive and negative acceleration?

Are you meaning applied energy vertically up and then a stop then acceleration vertically down?

Are you meaning applied energy vertically up and then a stop then acceleration vertically down?

Acceleration is a vector quantity. It has direction.
When reduced to 1 dimension this can be simply represented as positive and negative.
So vertically, you have acceleration in the upwards direction and acceleration in the downwards direction.

And this is merely your change in speed per unit time.
If you were travelling at 100 m/s and then over 100 s your speed was reduced to 0, that is (on average) an acceleration of -1 m/s.
If this continued for another 100 s your speed would be -100 m/s. If you then accelerate at 1 m/s, after 100 s your speed will be 0, then after another 100 s it would be 100 m/s.

Yet I am always changing if I am in motion so can it be a constant?

You can change in motion all you want as long as you keep a constant speed.

If so than why can't there be a constant RATE of acceleration?

Because acceleration is a rate of speed change at all times.

Quote from: Badxtoss on November 27, 2017, 10:02:18 AM

If so than why can't there be a constant RATE of acceleration?

Because acceleration is a rate of speed change at all times.

And speed is a rate of position change at all times.

Quote from: sceptimatic on November 27, 2017, 05:08:49 AM

I think what you're trying to say is, if the motor and pulley pull on the rope at a constant speed and then somehow has a power surge for half a second just as that rope is cut.

If that happens then we have the springboard effect. The rope would yank and the lift would accelerate on that immediate yank only before the rope snaps but then decelerate for a small portion of that half second before simply stopping dead and accelerating back down.

I think this answers my question. So, if I'm reading this right, then the amount of deceleration is down to how long the object in question has been accelerating for, rather than just how fast it's going?

Correct.

So an object that accelerates for one second to reach the same speed as an object that's been accelerating for an hour, is going to decelerate for less time before coming to a dead stop? That makes sense in line with everything else you've said, I just wasn't sure.

correct.

And if that's right, I think my last question is on what happens when the platform in question decelerates. Say, the lift in question decelerates when the rope's cut; it's losing power not at a constant speed, but it has no upwards acceleration, so would that cause a dead stop too?

No. It causes a ever reducing upward movement until it stops dead before acceleration downwards.

Let’s make this simple with a table:

Time Vel  Acc
0       0    1
1       1    1
2       2    1
3       3    1
4       4    1
5       5    1
6       6    1
7       7    1
8       8    1
9       9    1
10     10  1

From time 0 to 10 the acceleration is always 1. It is constant.

The rate of change can itself be constant over a period of time.

I'll make it as simple as I have done.
Acceleration is exactly what it means.
It means that the rate of speed changes positively.
It can never ever be constant until acceleration ceases to be acceleration.

Quote from: MicroBeta on November 27, 2017, 04:36:30 AM

Quote from: sceptimatic on November 26, 2017, 10:13:31 PM

<snip>
Of course you can slow down but you can never decelerate.
<snip>

Isn’t slowing down literally the definition of decelerate.

Mike

Slowing down naturally from the end point of acceleration before constant speed kicks in is natural deceleration.

What is unnatural declaration?

Now scepti, a nice simple one point for you:

You admit that you can have constant speed/velocity.
You claim that you can't have something constant when you have a change.
But speed/velocity is change in position per unit time.
If I start at your position and move with a constant velocity of 10 m/s, then after 1 second I am 10 m away from you, after 2 seconds I am 20 m away from you and so on.

So how can I have a constant velocity when my position is changing? It seems like according to you, the only constant velocity would be when your position doesn't change, and thus you have no velocity.

When an object travels the same distance every second, then the object is moving with constant velocity.

Quote from: sceptimatic on November 27, 2017, 01:35:52 PM

Are you meaning applied energy vertically up and then a stop then acceleration vertically down?

Acceleration is a vector quantity. It has direction.
When reduced to 1 dimension this can be simply represented as positive and negative.
So vertically, you have acceleration in the upwards direction and acceleration in the downwards direction.

And this is merely your change in speed per unit time.
If you were travelling at 100 m/s and then over 100 s your speed was reduced to 0, that is (on average) an acceleration of -1 m/s.
If this continued for another 100 s your speed would be -100 m/s. If you then accelerate at 1 m/s, after 100 s your speed will be 0, then after another 100 s it would be 100 m/s.

You're taking about vertical up and down rocket wise, right?
I don't agree with the negative.
The negative would be deceleration up after acceleration not acceleration down after the stop right after deceleration.

Quote from: sceptimatic on November 27, 2017, 01:40:05 PM

Quote from: Badxtoss on November 27, 2017, 10:02:18 AM

If so than why can't there be a constant RATE of acceleration?

Because acceleration is a rate of speed change at all times.

And speed is a rate of position change at all times.

If there were no position change there would be no arguments about movement, ever.

Quote from: sceptimatic on November 27, 2017, 04:45:57 AM

Quote from: MicroBeta on November 27, 2017, 04:36:30 AM

Quote from: sceptimatic on November 26, 2017, 10:13:31 PM

<snip>
Of course you can slow down but you can never decelerate.
<snip>

Isn’t slowing down literally the definition of decelerate.

Mike

Slowing down naturally from the end point of acceleration before constant speed kicks in is natural deceleration.

What is unnatural declaration?

Saying something like...." oh, I'd just like to say that I'm now a fierce dog."
Or something like that.
You could probably say something like " Oh, I'd like to say that I'm a scary ghost."

Stuff like that.

Quote from: Mainframes on November 27, 2017, 12:38:03 PM

Let’s make this simple with a table:

Time Vel  Acc
0       0    1
1       1    1
2       2    1
3       3    1
4       4    1
5       5    1
6       6    1
7       7    1
8       8    1
9       9    1
10     10  1

From time 0 to 10 the acceleration is always 1. It is constant.

The rate of change can itself be constant over a period of time.

I'll make it as simple as I have done.
Acceleration is exactly what it means.
It means that the rate of speed changes positively.
It can never ever be constant until acceleration ceases to be acceleration.

Wrong.  Acceleration can be positive or negative by definition.  As it means a change in velocity and velocity is a vector then acceleration can also be considered a change in direction as well.    Just because you don't understand it doesn't mean you get to change the definition.

Quote from: sceptimatic on November 27, 2017, 02:00:53 PM

Quote from: Mainframes on November 27, 2017, 12:38:03 PM

Let’s make this simple with a table:

Time Vel  Acc
0       0    1
1       1    1
2       2    1
3       3    1
4       4    1
5       5    1
6       6    1
7       7    1
8       8    1
9       9    1
10     10  1

From time 0 to 10 the acceleration is always 1. It is constant.

The rate of change can itself be constant over a period of time.

I'll make it as simple as I have done.
Acceleration is exactly what it means.
It means that the rate of speed changes positively.
It can never ever be constant until acceleration ceases to be acceleration.

Wrong.  Acceleration can be positive or negative by definition.  As it means a change in velocity and velocity is a vector then acceleration can also be considered a change in direction as well.    Just because you don't understand it doesn't mean you get to change the definition.

I don't see what point it has.
Acceleration is acceleration and to me it's all energy applied positive.
I don't see any negative in acceleration but I do in deceleration.

We really need to change many definitions to make things a bit more real.

Quote from: frenat on November 27, 2017, 02:45:54 PM

Quote from: sceptimatic on November 27, 2017, 02:00:53 PM

Quote from: Mainframes on November 27, 2017, 12:38:03 PM

Let’s make this simple with a table:

Time Vel  Acc
0       0    1
1       1    1
2       2    1
3       3    1
4       4    1
5       5    1
6       6    1
7       7    1
8       8    1
9       9    1
10     10  1

From time 0 to 10 the acceleration is always 1. It is constant.

The rate of change can itself be constant over a period of time.

I'll make it as simple as I have done.
Acceleration is exactly what it means.
It means that the rate of speed changes positively.
It can never ever be constant until acceleration ceases to be acceleration.

Wrong.  Acceleration can be positive or negative by definition.  As it means a change in velocity and velocity is a vector then acceleration can also be considered a change in direction as well.    Just because you don't understand it doesn't mean you get to change the definition.

I don't see what point it has.
Acceleration is acceleration and to me it's all energy applied positive.
I don't see any negative in acceleration but I do in deceleration.

We really need to change many definitions to make things a bit more real.

Acceleration is just a change in velocity.  It can be used either positive or negative.  Deceleration implies negative.  Just because you don't like the definition doesn't mean you can change it.

Quote from: Mainframes on November 27, 2017, 12:38:03 PM

Let’s make this simple with a table:

Time Vel  Acc
0       0    1
1       1    1
2       2    1
3       3    1
4       4    1
5       5    1
6       6    1
7       7    1
8       8    1
9       9    1
10     10  1

From time 0 to 10 the acceleration is always 1. It is constant.

The rate of change can itself be constant over a period of time.

I'll make it as simple as I have done.
Acceleration is exactly what it means.
It means that the rate of speed changes positively.
It can never ever be constant until acceleration ceases to be acceleration.

At any point from time 0 to time 10 is the acceleration anything other than 1?

Quote from: MicroBeta on November 27, 2017, 10:01:54 AM

Quote from: sceptimatic on November 27, 2017, 08:17:38 AM

Quote from: MicroBeta on November 27, 2017, 07:58:52 AM

I'm trying to understand.  You're saying we have an applied force without an acceleration and that force is the mass of the object?  In denpressure F=m?

No I'm not.
You cannot get to a constant speed without acceleration.

I still do not understand you.  Below it your post that I’m having trouble with. 

I’m saying that without acceleration and object’s speed cannot change.  Your post states “the applied force is the mass of the vehicle”.  What is unclear is how a mass can exert a force to stop an object without acceleration. 

Quote from: sceptimatic on November 27, 2017, 07:17:21 AM

In terms of slowing down the applied force is the mass of the vehicle. There is no acceleration.

Note that I’m using acceleration as signed quantity.  It’s either positive or negative (± acceleration). 

Mike

What do you mean by positive and negative acceleration?

Are you meaning applied energy vertically up and then a stop then acceleration vertically down?

Interesting but no, I’m not talking about “applied energy”.
 
Acceleration is a vector quantity.  In engineering the direction of an acceleration is important. However, for our discussion a positive value will be an acceleration and a negative value a deceleration.  Although the signs are analytically significant they are functionally identical.

Mike

Quote from: Badxtoss on November 27, 2017, 10:02:18 AM

Yet I am always changing if I am in motion so can it be a constant?

You can change in motion all you want as long as you keep a constant speed.

Quote from: Badxtoss on November 27, 2017, 10:02:18 AM

If so than why can't there be a constant RATE of acceleration?

Because acceleration is a rate of speed change at all times.

Yes, it's a RATE, of speed change.  Just like speed is a rate of distance change.
That rate can be constant.

I love reading these forums.. Its so ridiculous and hilarious!.

The direction of this chat has changed so drastically over 25 pages its incredible!

Keep up the good work!

Also, I only just created an account and this is my first post.. Only did so to say: Jane.. You're a moron. Thanks guys keep it up!

Also, I only just created an account and this is my first post.. Only did so to say: Jane.. You're a moron. Thanks guys keep it up!

Thanks! if you end up making more posts see how fun you find repeating the same things. I tried it once, got bored, this is actually interesting so I'm sticking with it.

Quote from: Jane

And if that's right, I think my last question is on what happens when the platform in question decelerates. Say, the lift in question decelerates when the rope's cut; it's losing power not at a constant speed, but it has no upwards acceleration, so would that cause a dead stop too?

No. It causes a ever reducing upward movement until it stops dead before acceleration downwards.

Thanks for the answers. This is the main bit that seemed weird. Just seems odd that if you use the lift and platform going at a constant speed again, the platform would keep going up for longer if the lift slowed for a moment, than if the lift just released it while it was going at a constant speed.
Though if it's being viewed from the perspective of acceleration less as a separate trait and more as a consequence of 'stored' velocity, it makes a kind of sense. Unintuitive, but I'm used to that.

Thanks for helping me understand your model.
The only bit I don't really understand is that it seems as though the platform would go up for longer if it was decelerated for a moment than if it was accelerated, given that the former seems to decelerate to zero while the latter decelerates temporarily (especially if we're only dealing with short bursts of acceleration) before coming to a dead stop.
I was thinking about it through the lens of approximation; like you brought up earlier, attaining a perfectly constant velocity is nigh-impossible, even if we can get close, so presumably short bursts of either acceleration or deceleration would function similarly to a constant velocity, but that doesn't seem to be the case. Might just be how I'm approaching it though.

Quote from: defender_of_truth on November 27, 2017, 02:52:03 AM

Quote from: sceptimatic on November 27, 2017, 02:50:12 AM

Quote from: defender_of_truth on November 27, 2017, 02:43:56 AM

I've heard it said that everyone is an expert in something. Scepti, out of curiosity, what is it that you consider yourself to be most skilled in?

I'm most skilled in being myself.

So... deflecting.

You asked me a question and I gave you an answer. How am I deflecting?

Strange. I would have thought the answer would be something about inventing. You know how your inventions met you over 20k a day. You bought a Bugatti Veyron remember?

Sceptitank full of shit.


Lol

Quote from: Jonny B Smart on November 26, 2017, 03:47:31 PM

“Open to alternative models” on this site means “prefer imagination to hundreds of years of accumulated scientific knowledge.”

This site is serious to the extent that it successfully damages public intelligence. Some of us have come here to do battle against misinformation. That is serious work (though exasperating). I don’t expect to convert the lost, but I hope inoculate the innocent by showing them that FE supporters’ logic and models ain’t worth their time.

How are you doing that? Leaving inside that pretentiousness, the only people not 'innoculated' are going to be more than capable of noticing the conspicuous absence of actual responses. It's only exasperating when you make it that way.
This should not be hard. If you are going to show that a model doesn't hold you have to take the time to understand it and see how it could work before responding. Launching straight into "You're wrong and everything you say is wrong," without trying to get clarification is just unutterably tedious for all involved, you Scepti and readers alike.

When someone makes claims that are patently and observably false in the real world I don't need to understand their model to tell them they are wrong. Cars trucks planes and bicycles do not immediately lose all foreword vertical motion, stop dead and fall or roll back down. If your model tells you this is what happens, your model is wrong, not a little wrong, not in need of some minor tweaking in the finer points, it is drastically fatally flawed wrong. No amount of understanding a model that makes such clearly wrong and foolish predictions will make those predictions true.
It becomes worse when said model invents new meanings for established scientific terms. And even worse when that model can not explain why these new understandings should be used or how they explain those predictions which are so clearly wrong. No amount of repeating or trying to explain how your model says that all objects moving vertically at a constant speed will stop dead when power is cut is going to make that prediction true, and it is clearly obvious to anyone who has ever driven a car, ridden a bike, or thrown a ball.

Quote from: sceptimatic on November 27, 2017, 01:35:52 PM

Quote from: MicroBeta on November 27, 2017, 10:01:54 AM

Quote from: sceptimatic on November 27, 2017, 08:17:38 AM

Quote from: MicroBeta on November 27, 2017, 07:58:52 AM

I'm trying to understand.  You're saying we have an applied force without an acceleration and that force is the mass of the object?  In denpressure F=m?

No I'm not.
You cannot get to a constant speed without acceleration.

I still do not understand you.  Below it your post that I’m having trouble with. 

I’m saying that without acceleration and object’s speed cannot change.  Your post states “the applied force is the mass of the vehicle”.  What is unclear is how a mass can exert a force to stop an object without acceleration. 

Quote from: sceptimatic on November 27, 2017, 07:17:21 AM

In terms of slowing down the applied force is the mass of the vehicle. There is no acceleration.

Note that I’m using acceleration as signed quantity.  It’s either positive or negative (± acceleration). 

Mike

What do you mean by positive and negative acceleration?

Are you meaning applied energy vertically up and then a stop then acceleration vertically down?

Interesting but no, I’m not talking about “applied energy”.
 
Acceleration is a vector quantity.  In engineering the direction of an acceleration is important. However, for our discussion a positive value will be an acceleration and a negative value a deceleration.  Although the signs are analytically significant they are functionally identical.

Mike

Ok so you have deceleration as the negative effect of acceleration.
Fair enough I can live with that.

It doesn't change anything I've said though.