Another Larry Brasfield Self-Aggrandizing Put-Down Anecdote

[Larry Brasfield]

"Active8" <reply2group@ndbbm.net> wrote in message news:3ohe0rdjzmmf.dlg@ID-222894.news.individual.net...

On Thu, 24 Mar 2005 11:31:41 -0800, Larry Brasfield wrote:
....
"Active8" <reply2group@ndbbm.net> wrote in message
news:195bgt3rf9uxe.dlg@ID-222894.news.individual.net...
[Old quote from a Brasfield post left for context.]
From: "Larry Brasfield" <donotspam_larry_brasfi...@hotmail.com
"Robert Monsen" <rcsurn...@comcast.net> wrote in message
No, as I recall, kinetic energy is 1/2 * m * v^2.
I recall seeing that claim from a high school physics teacher when
I was a smart-ass twerp. I posed the following puzzle to him:
A rocket car starts at rest, accellerating at a constant rate
because its thrust is constant. It is burning fuel at a constant
rate to produce that constant thrust. The kinetic energy of
the rocket car is allegedly M * V^2 / 2, so it is increasing
quadratically versus time. But the fuel consumed increases
only linearly with time. How can this be?

I would be interested in your take on this. My physics teacher
could not resolve it, (but, to his credit, that bothered him).
...
the whole thing that
sticks out as bs to me is that LB thinks that linearly changing mass
and quad changing energy is wrong. That makes no sense.

I asked this before: How could it be a puzzle
without seeming to be "wrong" on its face?

It wasn't wrong on it's face, but you asked him, "How can this be?"
It was a puzzle to you at the time.

Yes. I was just a twerp, not yet sophisticated enough
to look at all aspects of a problem.

I am puzzled as to why my puzzle puzzles you.

It was your confusion that puzzled me.

If you like, I was a confused child. In addition to the
distractions of the opposite sex, the usual teenager
troubles, and a few others, I made the very silly
mistake of not even thinking about the exhaust at
the time. My teacher's presentation of E=m v^2/2
was very good, and as I tried to incorporate that
into my meager other understandings, I failed and
so came to him, after class, to get that sorted out.
He gave it a try, but his effort did not succeed. [1]

Unless you were (or are) a most unusual young
person, you can surely identify with not being able
to figure stuff out oftentimes.

[1. As I recall that incident, I realize that he may
well have approached the problem by trying to
pull me out of my assumption with questions I
was unable to grasp. We had many other after-
school sessions where he often used the Socratic
method with me, and he was most often able to
get my questions resolved. He was (or is) at
least an intelligent person, if not brighter than I
knew at the time. So, I may have unintentionally
libeled him by forwarding my punk's impression
at the time ("could not resolve it") and presenting
it as fact. The most I can truthfully say is that he
did not resolve it for me, then. I thought about it
for some time afterward, thinking about the role
of the exhaust, and he may well have put that
finally pertinent thought into my head. ]

As I've said, it was proffered for fun. You seem
to have had fun with it. What is the problem?

You said, "I would be interested in your take on this."

Well, "Take" is subject to several interpretations.

My take was
that I'd not have puzzled over it. IIRC kinetic E came before
conservation of momentum in the class and it was the latter subject
where change in fuel mass came up and then only in "The Physics
Problem Solver." I still didn't puzzle over it.

Perhaps you refer to college courses. My anecdote
relates to a high school physics course for sophmores.
Maybe it was a school too podunk to cover momentum
before kinetic energy, (or I've forgotten), or maybe I
was just too dense or distracted to get it. Whichever
it is, you should not be taking my confusion compared
to your clarity of perception to indicate much. Stick
to the evidence and do not project what you "know"
into the gaps. Then it should either become clear or,
better yet, accurately and appropriately unclear.

[Active8's point and Brasfield's recast of it cut.]

With that adjustment, I agree with you.

So change the tense of "thinks" in:

Well, I can't be changing people's posts all the time just
so I can agree with them. That would be much like getting
stuck in front of a mirror, too enthralled to move on.

the whole thing that
sticks out as bs to me is that LB thinks that linearly changing mass
and quad changing energy is wrong. That makes no sense.

and know that it was as much bs then as it is now.

I'm not able to puzzle that out. Sorry.

Maybe I had fun with the total differential, but that depends on
what you consider fun.

I consider fun for you fun. It's not much more
complicated than that, really. Was that a grudging
admission? I hope so.

I'd call it interesting. Learning something
new is more fun.

Yes and yes. You've made it a little more interesting.

Best Regards,

Really? If so, likewise.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Robert Monsen]

Active8 wrote:

I'll have to check google for that 'cause it's not in my seb headers
(I only pulled 100) I went ahead and did the total differential with
a changing mass (i think I left that out of the accel/velocity part)
and integrated that and ended up with a sum of 2 energies for the
total kinetic energy. I think that's what JT suggested I do (write
it wrt time)

One of the terms looks like it contains impulse and I forget what
you multiply impulse by to get E (I could have checked the
dimensions) but it looks normal.

Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket). Just
looking at those two facts, it's a puzzle, because it seems to
contradict conservation of energy. The answer is to also consider the ke
of the burnt fuel.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Jim Thompson]

On Thu, 24 Mar 2005 17:32:13 -0800, Robert Monsen
<rcsurname@comcast.net> wrote:

Active8 wrote:
I'll have to check google for that 'cause it's not in my seb headers
(I only pulled 100) I went ahead and did the total differential with
a changing mass (i think I left that out of the accel/velocity part)
and integrated that and ended up with a sum of 2 energies for the
total kinetic energy. I think that's what JT suggested I do (write
it wrt time)

One of the terms looks like it contains impulse and I forget what
you multiply impulse by to get E (I could have checked the
dimensions) but it looks normal.


Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket). Just
looking at those two facts, it's a puzzle, because it seems to
contradict conservation of energy. The answer is to also consider the ke
of the burnt fuel.

There you go, the statement of the problem is contradictory... sucker
bait.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[John Larkin]

On Thu, 24 Mar 2005 17:32:13 -0800, Robert Monsen
<rcsurname@comcast.net> wrote:

Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket).

Why is that a puzzle? It starts out at zero efficiency and, just
before it runs out of fuel, it's worked its way up to rotten
efficiency; that violates no physical laws.

John

 

[Ratch]

"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:8vmdnayg1cSD997fRVn-oQ@comcast.com...

Active8 wrote:
I'll have to check google for that 'cause it's not in my seb headers
(I only pulled 100) I went ahead and did the total differential with
a changing mass (i think I left that out of the accel/velocity part)
and integrated that and ended up with a sum of 2 energies for the
total kinetic energy. I think that's what JT suggested I do (write
it wrt time)

One of the terms looks like it contains impulse and I forget what
you multiply impulse by to get E (I could have checked the
dimensions) but it looks normal.


Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket). Just
looking at those two facts, it's a puzzle, because it seems to
contradict conservation of energy. The answer is to also consider the ke
of the burnt fuel.

The static power and thereby force of the engine is constant if the
throttle is fixed. If the rocket is tied down, no static energy is
transfered from the fuel to the kinetic energy (KE) of the rocket. The
kinetic power increases linearly with velocity, assuming constant
acceleration. Since P = F*v = F*a*t, twice the power is being converted to
KE at the end of 10 sec as compared to 5 sec. The distance travelled is
three times as long from 5 sec to 10 secs as compared to 0 sec to 5 sec
(˝a*t˛). If the force is constant, and the distance is three times as long,
it should be no suprise that that 3 times the energy is accumulated from 5
sec to 10 sec as compared from 0 sec to 5 sec. Ratch

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[John Larkin]

On Thu, 24 Mar 2005 19:42:44 -0800, Robert Monsen
<rcsurname@comcast.net> wrote:

John Larkin wrote:
On Thu, 24 Mar 2005 17:32:13 -0800, Robert Monsen
rcsurname@comcast.net> wrote:

Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket).

Why is that a puzzle? It starts out at zero efficiency and, just
before it runs out of fuel, it's worked its way up to rotten
efficiency; that violates no physical laws.


Actually, that doesn't help at all. We all know it's OK, and that
rockets don't violate conservation of energy. The puzzle is why do these
two ways of looking at the energy at a given time give different answers?

What "answers"? An observation that a phenomenon has a curve says
nothing about the quantitative issues. The original "puzzle" was a
sloppy, qualitative look at the way a rocket functions, and created a
bogus paradox by assuming that a squared-something curve somehow has
to increase enormously without limit and punch a hole in the sky or
something.

If you don't do the math, you can't complain about "different
answers." The only different answers are the right one, and all the
rest.

John

 

[Active8]

On Thu, 24 Mar 2005 13:48:06 -0800, Larry Brasfield wrote:

"Active8" <reply2group@ndbbm.net> wrote in message news:3ohe0rdjzmmf.dlg@ID-222894.news.individual.net...
On Thu, 24 Mar 2005 11:31:41 -0800, Larry Brasfield wrote:
snip

It was your confusion that puzzled me.

If you like, I was a confused child. In addition to the

I'm a confused adult. Biased media confuses me on the issues and
facts. Only researching legislative proceedings and executive orders
would that, I think. Differing views on history and philosophy leave
me out there, sometimes.

distractions of the opposite sex, the usual teenager
troubles, and a few others, I made the very silly
mistake of not even thinking about the exhaust at
the time. My teacher's presentation of E=m v^2/2

F the exhaust. If a constant burn causes a constant force ->
constant a... v = at and energy just happens to be proportional to
v^2.

was very good, and as I tried to incorporate that
into my meager other understandings, I failed and
so came to him, after class, to get that sorted out.
He gave it a try, but his effort did not succeed. [1]

Unless you were (or are) a most unusual young
person, you can surely identify with not being able
to figure stuff out oftentimes.

[1. As I recall that incident, I realize that he may
well have approached the problem by trying to
pull me out of my assumption with questions I
was unable to grasp. We had many other after-
school sessions where he often used the Socratic

What did Socrates do? I don't recall that.

method with me, and he was most often able to
get my questions resolved. He was (or is) at
least an intelligent person, if not brighter than I
knew at the time. So, I may have unintentionally
libeled him by forwarding my punk's impression
at the time ("could not resolve it") and presenting
it as fact. The most I can truthfully say is that he
did not resolve it for me, then. I thought about it
for some time afterward, thinking about the role
of the exhaust, and he may well have put that
finally pertinent thought into my head. ]

The mv conservation approach has it's uses but that doesn't make it
the only way to solve the problem. I had a physics exam with an
elevator problem in multiple parts. I tried working it from F = ma
instead of U + K = E . F'd it all up.

As I've said, it was proffered for fun. You seem
to have had fun with it. What is the problem?

You said, "I would be interested in your take on this."

Well, "Take" is subject to several interpretations.

My take was
that I'd not have puzzled over it. IIRC kinetic E came before
conservation of momentum in the class and it was the latter subject
where change in fuel mass came up and then only in "The Physics
Problem Solver." I still didn't puzzle over it.

And F came before E, too. They didn't really teach me about working
backwards, though at the time, I'd have worked an amplifier
backwards.

Perhaps you refer to college courses. My anecdote

I had advanced Physics (that's with calculus) in HS. Then I moved to
a podunk school with a space-brain teacher showing pictures from his
telescope and figuring how fast to hit a tree with a snow ball to
get it to melt. He let me study a Schaum's - taught myself a bit. A
Chinese student who'd already passed calculus taught me calculus
with the help of MD public TV vids. I learned calc better than
physics.

relates to a high school physics course for sophmores.
Maybe it was a school too podunk to cover momentum

It was the other way.

before kinetic energy, (or I've forgotten), or maybe I
was just too dense or distracted to get it. Whichever
it is, you should not be taking my confusion compared
to your clarity of perception to indicate much. Stick

The question didn't even come up in my mind back then. My clarity
now is partly intuitive. I'm not going to question .5*m*v^2 at low
velocities.

to the evidence and do not project what you "know"
into the gaps. Then it should either become clear or,
better yet, accurately and appropriately unclear.

[Active8's point and Brasfield's recast of it cut.]
With that adjustment, I agree with you.

So change the tense of "thinks" in:

Well, I can't be changing people's posts all the time just
so I can agree with them. That would be much like getting
stuck in front of a mirror, too enthralled to move on.

Well, I had no indication that you didn't still think there was a
conundrum. I meant that you can now change the tense and it doesn't
change anything else. If my words aren't totally clear and you think
you know what I am trying to say, I'm not sure that what you hear is
what I mean. IOW, I'm not going to nitpick my own words to death
tonight. None of this means a damned thing anyway.

the whole thing that
sticks out as bs to me is that LB thinks that linearly changing mass
and quad changing energy is wrong. That makes no sense.

and know that it was as much bs then as it is now.

I'm not able to puzzle that out. Sorry.

Newtonian Physics hasn't changed.

Maybe I had fun with the total differential, but that depends on
what you consider fun.

I consider fun for you fun. It's not much more
complicated than that, really. Was that a grudging
admission? I hope so.

No, it wasn't fun, just interesting to look at it as a TD rather
than a momentum thing since in physics I, we didn't know partial
derivatives and therefore couldn't play with them.

I'd call it interesting. Learning something
new is more fun.

Yes and yes. You've made it a little more interesting.

Best Regards,

Really? If so, likewise.

I generally harbor no malice towards others. When I do, I try to get
rid of it. Negative stuff just eats you from within. I've only
changed my sig block for Burridge when I was messing with his thick
head, which he asked for, BTW.

If anybody find an obit on him over there, let us know.
--
Best Regards,
Mike

 

[Active8]

On Thu, 24 Mar 2005 20:54:31 -0600, Ratch wrote:

"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:8vmdnayg1cSD997fRVn-oQ@comcast.com...
Active8 wrote:
I'll have to check google for that 'cause it's not in my seb headers
(I only pulled 100) I went ahead and did the total differential with
a changing mass (i think I left that out of the accel/velocity part)
and integrated that and ended up with a sum of 2 energies for the
total kinetic energy. I think that's what JT suggested I do (write
it wrt time)

One of the terms looks like it contains impulse and I forget what
you multiply impulse by to get E (I could have checked the
dimensions) but it looks normal.


Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket). Just
looking at those two facts, it's a puzzle, because it seems to
contradict conservation of energy. The answer is to also consider the ke
of the burnt fuel.

The static power and thereby force of the engine is constant if the
throttle is fixed. If the rocket is tied down, no static energy is
transfered from the fuel to the kinetic energy (KE) of the rocket. The
kinetic power increases linearly with velocity, assuming constant
acceleration. Since P = F*v = F*a*t, twice the power is being converted to
KE at the end of 10 sec as compared to 5 sec. The distance travelled is
three times as long from 5 sec to 10 secs as compared to 0 sec to 5 sec
(˝a*t˛). If the force is constant, and the distance is three times as long,
it should be no suprise that that 3 times the energy is accumulated from 5
sec to 10 sec as compared from 0 sec to 5 sec. Ratch

You put that another way in your other post but what does E*3 have
to do with v^2 ?
--
Best Regards,
Mike

 

[Ratch]

"Active8" <reply2group@ndbbm.net> wrote in message
news:ai11tqckqpxp.dlg@ID-222894.news.individual.net...

On Thu, 24 Mar 2005 20:54:31 -0600, Ratch wrote:

"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:8vmdnayg1cSD997fRVn-oQ@comcast.com...
Active8 wrote:
I'll have to check google for that 'cause it's not in my seb headers
(I only pulled 100) I went ahead and did the total differential with
a changing mass (i think I left that out of the accel/velocity part)
and integrated that and ended up with a sum of 2 energies for the
total kinetic energy. I think that's what JT suggested I do (write
it wrt time)

One of the terms looks like it contains impulse and I forget what
you multiply impulse by to get E (I could have checked the
dimensions) but it looks normal.


Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket). Just
looking at those two facts, it's a puzzle, because it seems to
contradict conservation of energy. The answer is to also consider the
ke
of the burnt fuel.

The static power and thereby force of the engine is constant if the
throttle is fixed. If the rocket is tied down, no static energy is
transfered from the fuel to the kinetic energy (KE) of the rocket. The
kinetic power increases linearly with velocity, assuming constant
acceleration. Since P = F*v = F*a*t, twice the power is being
converted to
KE at the end of 10 sec as compared to 5 sec. The distance travelled is
three times as long from 5 sec to 10 secs as compared to 0 sec to 5 sec
(˝a*t˛). If the force is constant, and the distance is three times as
long,
it should be no suprise that that 3 times the energy is accumulated from
5
sec to 10 sec as compared from 0 sec to 5 sec. Ratch

You put that another way in your other post but what does E*3 have
to do with v^2 ?

Sorry, I thought I made it clear. E = W = 1/2 m*v^2. Assume m = 2, a = 1 .
At t = 5, v = a*t = 5, W = 1/2 * 2*5^2 = 25, s = 1/2 a*t^2 = 12.5 . At t =
10, v = a*t = 10, W = 1/2 * 2*10^2 = 100, s = 1/2 a*t^2 = 50 . Distance
traveled from 0 to 5 secs = 12.5 . Distance traveled from 5 to 10 secs =
37.5 . Three time the distance traveled in the same time, constant thrust
or force makes 3 times the KE accumulated from 5 to 10 sec as compared to 0
to 5 secs. Velocity and kinetic power increase proportionately to time,
Distance travelled and KE increase proportionately to time squared. So to
answer your question, the v^2 relationship gives a 3*distance during the
second equal time interval when compared to the first identical time
interval. That causes the KE to increase by 3 times during the second
identical time interval as compared to the first time interval. Ratch

Best Regards,
Mike

 

[Fred Bloggs]

Larry Brasfield wrote:

You are going beyond the evidence, pal. The
antecdote, relating to an event in 1967, bears
on my thinking at that time. To get from there
to "LB thinks" at this time, would required an
extremely limited view of my educatability and
surmises about intervening processes that go
way beyond the evidence.

We have plenty of evidence that you are NOT well- educated. Much of your
sentence structure is malformed and contradictory bs that says nothing.
Your knowledge of engineering is also elementary and dysfunctional, now
and in the past. That is why you are a punk programmer working for the
AR Group in an insignificant role.

 

[Active8]

On Thu, 24 Mar 2005 17:32:13 -0800, Robert Monsen wrote:

Active8 wrote:
I'll have to check google for that 'cause it's not in my seb headers
(I only pulled 100) I went ahead and did the total differential with
a changing mass (i think I left that out of the accel/velocity part)
and integrated that and ended up with a sum of 2 energies for the
total kinetic energy. I think that's what JT suggested I do (write
it wrt time)

One of the terms looks like it contains impulse and I forget what
you multiply impulse by to get E (I could have checked the
dimensions) but it looks normal.


Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically

How many times... how many different ways... can I say it. There *is
no puzzle*. If a linear fuel mass expenditure really gave a constant
acceleration or constant power, that's fine. Check your old text.
They start by showing that v = at and then a = F/m. Then they show
that KE varies quadratically with v. If you can accept that, there's
no puzzle.

When one assumes that a linear change of one dimension should
produce a linear change in a derived unit it's called flawed logic.
At least that's what I called it.

with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket). Just
looking at those two facts, it's a puzzle, because it seems to
contradict conservation of energy. The answer is to also consider the ke
of the burnt fuel.

Or use momentums and convert to energy later. With your way, you
have to guess at the relation between fuel expenditure and thrust.
With conservation of momentum, you have to guess the velocity of the
ejected fuel mass.

Now we didn't have partial derivatives as tools in physics I, but
here's what I did:

let D be the round D

k = fuel mass expenditure wrt time
M = initial mass of rocket

m = M - kt instantaneous mass of rocket

1
KE = --- (M - kt)a^2 t^2
2

expand that

DE 1 2
-- = - v
Dm 2

DE 2
-- = mat - kat
Dv

1 2 2
DE = - v dm + mat dv - kat dv
2


dE 1 2 dm dv 2 dv
-- = - v -- + mv -- - kat --
dt 2 dt dt dt

dE 1 2 2
-- = - kv + mav - kv
dt 2

1 2 2
dE = - kv dt + Fv dt = kv dt
2

integrate
1 2 2
E = - kv t + Fvt = kv t
2

1 2
E = - mv + Fx - kxv
2

.
.. . Total energy = KE + thrust energy - exhaust energy

QED
--
Best Regards,
Mike

 

[Fred Bloggs]

Active8 wrote:

On Thu, 24 Mar 2005 13:48:06 -0800, Larry Brasfield wrote:


"Active8" <reply2group@ndbbm.net> wrote in message news:3ohe0rdjzmmf.dlg@ID-222894.news.individual.net...

On Thu, 24 Mar 2005 11:31:41 -0800, Larry Brasfield wrote:




What did Socrates do? I don't recall that.

That p.o.s. doesn't know. He only brought that up because I first
referred to it in a response JF regarding Brasfield's pedophile-like
technique of capturing the attention of juvenile punk OPs.

BTW- have you seen the pseudo-intellectual give a coherent explanation
of his so-called puzzle...

 

[Ratch]

"Active8" <reply2group@ndbbm.net> wrote in message
news:ai11tqckqpxp.dlg@ID-222894.news.individual.net...

On Thu, 24 Mar 2005 20:54:31 -0600, Ratch wrote:

"Robert Monsen" <rcsurname@comcast.net> wrote in message
news:8vmdnayg1cSD997fRVn-oQ@comcast.com...
Active8 wrote:
I'll have to check google for that 'cause it's not in my seb headers
(I only pulled 100) I went ahead and did the total differential with
a changing mass (i think I left that out of the accel/velocity part)
and integrated that and ended up with a sum of 2 energies for the
total kinetic energy. I think that's what JT suggested I do (write
it wrt time)

One of the terms looks like it contains impulse and I forget what
you multiply impulse by to get E (I could have checked the
dimensions) but it looks normal.


Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket). Just
looking at those two facts, it's a puzzle, because it seems to
contradict conservation of energy. The answer is to also consider the
ke
of the burnt fuel.

The static power and thereby force of the engine is constant if the
throttle is fixed. If the rocket is tied down, no static energy is
transfered from the fuel to the kinetic energy (KE) of the rocket. The
kinetic power increases linearly with velocity, assuming constant
acceleration. Since P = F*v = F*a*t, twice the power is being
converted to
KE at the end of 10 sec as compared to 5 sec. The distance travelled is
three times as long from 5 sec to 10 secs as compared to 0 sec to 5 sec
(˝a*t˛). If the force is constant, and the distance is three times as
long,
it should be no suprise that that 3 times the energy is accumulated from
5
sec to 10 sec as compared from 0 sec to 5 sec. Ratch

You put that another way in your other post but what does E*3 have
to do with v^2 ?

Look at it another way, the conversion of the rocket fuel into thrust is not
a proportional relationship to KE. For instance, if a rocket burns without
sufficient force to take off, it can shoot its whole fuel energy wad and
accumulate no KE at all. If a rocket is going fast, it accumulates KE at a
faster rate than it did going slow. I proved that above. So it is a
mistake to say that when a rocket is burning and expending its energy at a
constant rate, its KE is increasing proportionately. Ratch

 

[Active8]

On Thu, 24 Mar 2005 20:20:04 -0800, John Larkin wrote:

On Thu, 24 Mar 2005 19:42:44 -0800, Robert Monsen
rcsurname@comcast.net> wrote:

John Larkin wrote:
On Thu, 24 Mar 2005 17:32:13 -0800, Robert Monsen
rcsurname@comcast.net> wrote:

Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket).

Why is that a puzzle? It starts out at zero efficiency and, just
before it runs out of fuel, it's worked its way up to rotten
efficiency; that violates no physical laws.


Actually, that doesn't help at all. We all know it's OK, and that
rockets don't violate conservation of energy. The puzzle is why do these
two ways of looking at the energy at a given time give different answers?


What "answers"? An observation that a phenomenon has a curve says
nothing about the quantitative issues. The original "puzzle" was a
sloppy, qualitative look at the way a rocket functions, and created a
bogus paradox by assuming that a squared-something curve somehow has
to increase enormously without limit and punch a hole in the sky or
something.

That's sort of what I've been trying to tell Larry all along.
Different equations for different things don't have to have the same
type of curve.

Actually, the flaw was the assumption that a linearly varying SI
unit should dictate a linearly varying derived unit. It's like
saying that if the diameter increases linearly, so should the area.

If you don't do the math, you can't complain about "different
answers."

Amen, bro. Maybe it was intuition, but I bitched before doing the
math becasue the flawed logic was all too apparent to me. I just
tried a different approach for grins.

The only different answers are the right one, and all the
rest.

LOL
--
Best Regards,
Mike

 

[Robert Monsen]

John Larkin wrote:

On Thu, 24 Mar 2005 19:42:44 -0800, Robert Monsen
rcsurname@comcast.net> wrote:


John Larkin wrote:

On Thu, 24 Mar 2005 17:32:13 -0800, Robert Monsen
rcsurname@comcast.net> wrote:


Actually, the puzzle is that the power is constant (a constant rate of
fuel burn) but the rocket's kinetic energy is increasing quadratically
with time, since the velocity is increasing linearly (if you ignore
changes in acceleration due to the changing mass of the rocket).

Why is that a puzzle? It starts out at zero efficiency and, just
before it runs out of fuel, it's worked its way up to rotten
efficiency; that violates no physical laws.


Actually, that doesn't help at all. We all know it's OK, and that
rockets don't violate conservation of energy. The puzzle is why do these
two ways of looking at the energy at a given time give different answers?



What "answers"? An observation that a phenomenon has a curve says
nothing about the quantitative issues.

Not true. You can determine that the two aren't equal for all t. That is
all that is really required, and is the source of the puzzle. When I
said 'answers', I obviously meant energy of rocket at time t, and energy
expended in fuel up till time t. Sorry for any confusion.

The original "puzzle" was a

sloppy, qualitative look at the way a rocket functions, and created a
bogus paradox by assuming that a squared-something curve somehow has
to increase enormously without limit and punch a hole in the sky or
something.

Except for the last part, I agree. However, that doesn't make it a bad
puzzler. Some of those old martin gardner puzzlers were quite devious.
Riddles are notoriously devious, and mislead you in whatever way they
can. Mysteries are fun for that very reason.

If you don't do the math, you can't complain about "different
answers." The only different answers are the right one, and all the
rest.

It was similar to the 'Questions' section at the end of chapters in my
first college physics book. They were generally qualitative puzzlers
like this, that were intended to make you think about what could be
happening.

Here is an example:

"A canoeist in a still pond can reach shore by jerking sharply on the
rope attached to the bow of the canoe. How do you explain this? (yes she
can! - it's true)" (question 11, chap 9, "Physics, Part I", Halliday and
Resnick, 3rd edition).

Sadly, I don't know the answer to this, other than some hand wavings
about friction of the water on the boat. The chapter is entitled
"Conservation of Linear Momentum", so it probably has something to do
with conservation of momentum... Maybe somebody with a few more
intact brain cells left over from college can explain it.

My issue (and Fred's, I'm gussing) wasn't really about the puzzler
itself, it was with the "Let's see if we can show this guy up" attitude
it was originally posted with. However, I like these kinds of things;
they are more fun than crossword puzzles. Of course, I knew that it had
to be the fuel, but I wanted to come up with an equation the proved that
KE(fuel) + KE(rocket) = PE expended for all time (until the thing runs
out of fuel). He thus had me digging out old physics text books. It was
fun, even though I didn't succeed in coming up with the equation.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[Fred Bloggs]

Robert Monsen wrote:

John Larkin wrote:

On Thu, 24 Mar 2005 19:42:44 -0800, Robert Monsen
rcsurname@comcast.net> wrote:


John Larkin wrote:

On Thu, 24 Mar 2005 17:32:13 -0800, Robert Monsen
rcsurname@comcast.net> wrote:


Actually, the puzzle is that the power is constant (a constant rate
of fuel burn) but the rocket's kinetic energy is increasing
quadratically with time, since the velocity is increasing linearly
(if you ignore changes in acceleration due to the changing mass of
the rocket).


Why is that a puzzle? It starts out at zero efficiency and, just
before it runs out of fuel, it's worked its way up to rotten
efficiency; that violates no physical laws.


Actually, that doesn't help at all. We all know it's OK, and that
rockets don't violate conservation of energy. The puzzle is why do
these two ways of looking at the energy at a given time give
different answers?



What "answers"? An observation that a phenomenon has a curve says
nothing about the quantitative issues.


Not true. You can determine that the two aren't equal for all t. That is
all that is really required, and is the source of the puzzle. When I
said 'answers', I obviously meant energy of rocket at time t, and energy
expended in fuel up till time t. Sorry for any confusion.

The original "puzzle" was a

sloppy, qualitative look at the way a rocket functions, and created a
bogus paradox by assuming that a squared-something curve somehow has
to increase enormously without limit and punch a hole in the sky or
something.


Except for the last part, I agree. However, that doesn't make it a bad
puzzler. Some of those old martin gardner puzzlers were quite devious.
Riddles are notoriously devious, and mislead you in whatever way they
can. Mysteries are fun for that very reason.

If you don't do the math, you can't complain about "different
answers." The only different answers are the right one, and all the
rest.


It was similar to the 'Questions' section at the end of chapters in my
first college physics book. They were generally qualitative puzzlers
like this, that were intended to make you think about what could be
happening.

Here is an example:

"A canoeist in a still pond can reach shore by jerking sharply on the
rope attached to the bow of the canoe. How do you explain this? (yes she
can! - it's true)" (question 11, chap 9, "Physics, Part I", Halliday and
Resnick, 3rd edition).

I solved every single problem in that book some 100 years ago when I
took my first course, but don't remember that one. However, the "jerk"
leads me too suspect you might want to look at what they define as
"impact" which imparts a step momentum to the canoe which carries it to
shore.

Sadly, I don't know the answer to this, other than some hand wavings
about friction of the water on the boat. The chapter is entitled
"Conservation of Linear Momentum", so it probably has something to do
with conservation of momentum... Maybe somebody with a few more
intact brain cells left over from college can explain it.

My issue (and Fred's, I'm gussing) wasn't really about the puzzler
itself, it was with the "Let's see if we can show this guy up" attitude
it was originally posted with. However, I like these kinds of things;
they are more fun than crossword puzzles. Of course, I knew that it had
to be the fuel, but I wanted to come up with an equation the proved that
KE(fuel) + KE(rocket) = PE expended for all time (until the thing runs
out of fuel). He thus had me digging out old physics text books. It was
fun, even though I didn't succeed in coming up with the equation.

You can do it- forget digging out equations- use your understanding of
momentum and common sense.

 

[Active8]

On Fri, 25 Mar 2005 00:17:48 -0600, Ratch wrote:

Look at it another way, the conversion of the rocket fuel into thrust is not
a proportional relationship to KE.

Now you're becoming a bore really - Read my posts *and* the OP.
I've been saying something close to that all along, to wit: KE is
proportional to the square of velocity which is proportional to
acceleration which is proportional to force or thrust. You don't
have to ponder/know/guess the conversion of fuel to thrust or the
efficiency to see that. At least I don't, nor others here that are
most likely sitting back laughing at this bullsh*t.

For instance, if a rocket burns without
sufficient force to take off, it can shoot its whole fuel energy wad and
accumulate no KE at all. If a rocket is going fast, it accumulates KE at a
faster rate than it did going slow. I proved that above. So it is a
mistake to say that when a rocket is burning and expending its energy at a
constant rate, its KE is increasing proportionately. Ratch

I said it better with my math - once with conservation of momentum
principles and once with conservation of energy principles. Thanks
for writing out your thoughts with equations, but as you said, the
non-puzzle was why a linearly varying quantity (mass) does not
produce another linear varying quantity (energy)

To say that v^2 is proportional to 3*KE is nothing more than
plugging in numbers. It kind of obscured the real problem with the
non-puzzle, at least for me. And all those words.

Thanks again.
--
Best Regards,
Mike

 

[Active8]

On Thu, 24 Mar 2005 23:12:10 -0800, Robert Monsen wrote:

John Larkin wrote:
On Thu, 24 Mar 2005 19:42:44 -0800, Robert Monsen
snip

"A canoeist in a still pond can reach shore by jerking sharply on the
rope attached to the bow of the canoe. How do you explain this? (yes she
can! - it's true)" (question 11, chap 9, "Physics, Part I", Halliday and
Resnick, 3rd edition).

That's the book I had in HS and used at U of PA. I bought it when I
moved to a new school. And that's a damned good question. Thanks,
I'll remember to look at those noodle twisters when I'm bored.

Sadly, I don't know the answer to this, other than some hand wavings
about friction of the water on the boat. The chapter is entitled
"Conservation of Linear Momentum", so it probably has something to do
with conservation of momentum... Maybe somebody with a few more
intact brain cells left over from college can explain it.

I think it's because the energy she uses to jerk her hand is
internal to her [strike lewd remark] body. If she stopped the motion
on her own, an oppositely directed energy from inside her body would
negate that. But the rope stops her motion and that is external to
her body.

I don't know for sure that I ever had any brain cells. I though this
was all an illusion.

My issue (and Fred's, I'm gussing) wasn't really about the puzzler
itself, it was with the "Let's see if we can show this guy up" attitude
it was originally posted with. However, I like these kinds of things;

Yup and yup.

they are more fun than crossword puzzles. Of course, I knew that it had
to be the fuel, but I wanted to come up with an equation the proved that
KE(fuel) + KE(rocket) = PE expended for all time (until the thing runs
out of fuel). He thus had me digging out old physics text books. It was
fun, even though I didn't succeed in coming up with the equation.

Free your mind Neo
--
Best Regards,
Mike

 

[John Woodgate]

I read in sci.electronics.design that Robert Monsen
<rcsurname@comcast.net> wrote (in <9badnW-OYcBWJN7fRVn-iA@comcast.com&gt
about 'Another Larry Brasfield Self-Aggrandizing Put-Down Anecdote', on
Thu, 24 Mar 2005:

Of course, I knew that it had to be the fuel, but I wanted to come up
with an equation the proved that KE(fuel) + KE(rocket) = PE expended
for all time (until the thing runs out of fuel). He thus had me digging
out old physics text books. It was fun, even though I didn't succeed in
coming up with the equation.

Some of the PE is the chemical energy in the unburned fuel. It's also
necessary to know how much of that is released by combustion.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Active8]

On Fri, 25 Mar 2005 06:00:46 GMT, Fred Bloggs wrote:

Active8 wrote:
On Thu, 24 Mar 2005 13:48:06 -0800, Larry Brasfield wrote:

"Active8" <reply2group@ndbbm.net> wrote in message news:3ohe0rdjzmmf.dlg@ID-222894.news.individual.net...

On Thu, 24 Mar 2005 11:31:41 -0800, Larry Brasfield wrote:



What did Socrates do? I don't recall that.

That p.o.s. doesn't know. He only brought that up because I first
referred to it in a response JF regarding Brasfield's pedophile-like
technique of capturing the attention of juvenile punk OPs.

This must be a clue:

http://www.mindspring.com/~mfpatton/sclinic.htm

I got the gist after a few paras. I don't know in what context you
used the phrase, but I'll venture that Larry meant that his teacher
just kept on until he gave in.

BTW- have you seen the pseudo-intellectual give a coherent explanation
of his so-called puzzle...

No. I did it twice with math and with too many attempts at words.
I'm going to take the salient advice of you and some others, if I
can control myself If I can't point out the flawed logic with
words on the first try, I'll just do and show the math if so
inclined.

Getting that in ascii was a PITA. Maybe mathematica to html would be
better.
--
Best Regards,
Mike