Question on forces acting on an aircraft in climb
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes
on
0 Posts
Please describe a net force that does not produce an acceleration.
Are you sure you can't have a force without acceleration?
Join Date: Jun 2010
Location: Canada
Age: 37
Posts: 382
Likes: 0
Received 0 Likes
on
0 Posts
regarding your first point, yes that would be apparent weight which would be in the non-inertial reference frame!
no, im not confused about anything! it was a general concept about the equation F=MA and how i stated that the equation doesn't explain everything! it was more for conceptualization purposes. if you had a box on a carpet floor, you have friction resisting it's movement so if you apply a small force, there is no acceleration. yes, if you have a NET force there will be acceleration.
No, you can't. You are confused on that one.Force is measured in kg*m/s2.If you dont HAVE any m/s2, you don't have a Force! Please describe a net force that does not produce an acceleration.
Join Date: Jun 2010
Location: Canada
Age: 37
Posts: 382
Likes: 0
Received 0 Likes
on
0 Posts
The Gravity Equation quantifies Gravity. It doesn't explain it.
Say the differential pressure inside the hull of my aircraft is 8 p.s.i. The net force on a passenger door with an area of 1,000 square inches is 8,000 lbs.
Are you sure you can't have a force without acceleration?
Are you sure you can't have a force without acceleration?
Say the differential pressure inside the hull of my aircraft is 8 p.s.i. The net force on a passenger door with an area of 1,000 square inches is 8,000 lbs.
It is NOT a net force, however, as the structure of the aircraft exerts an EQUAL and OPpOSITE force, leaving a NET force of zero.
if you had a box on a carpet floor, you have friction resisting it's movement so if you apply a small force, there is no acceleration.
wiz... so because one equation doesn't explain the whole concept of gravity, it shouldn't be used IN the explanation?! wow you really come up with some good things. for starters, it's very valuable as it shows WHAT FACTORS AFFECT GRAVITY!!!
To try and get this back on track and summarise my points-
By the ISO definition of weight, force due to acceleration of a mass is weight from the frame of reference of the object being accelerated, so an aircraft in a turn can be said to increase in weight.
..And PBL is wrong about what his scales will read as he does not appear to understand the concept that angular velocity has an absolute value, and therefore is present in any inertial frame of reference.
Oh, and I though the reason for the high tide on the far side of the Earth was pretty cool!!
By the ISO definition of weight, force due to acceleration of a mass is weight from the frame of reference of the object being accelerated, so an aircraft in a turn can be said to increase in weight.
..And PBL is wrong about what his scales will read as he does not appear to understand the concept that angular velocity has an absolute value, and therefore is present in any inertial frame of reference.
Oh, and I though the reason for the high tide on the far side of the Earth was pretty cool!!
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes
on
0 Posts
I would think that in most discussions where one first defines carefully what each word, like "force" and "weight" really mean.... you will find, that what you "feel" in a turn is referred to as "apparent weight".
So yes, it can be "said to" increase in weight... but only after you've defined carefully what the word really says...
"In the beginning was the Word". Remember? But then we went and used the same word for so many related and similar but not identical concepts.... and then thought the word meant the same thing every time.
You've just noticed it yourself... by finding you have to substitute "net force" for "force"...
CJ
So yes, it can be "said to" increase in weight... but only after you've defined carefully what the word really says...
"In the beginning was the Word". Remember? But then we went and used the same word for so many related and similar but not identical concepts.... and then thought the word meant the same thing every time.
You've just noticed it yourself... by finding you have to substitute "net force" for "force"...
CJ
Christian,
All fair comment. I would point at that, in most technical discussions, ISO values are usually the ones used. By THAT definition, what you refer to as "Apparent weight" would simply be "Weight".
As I'v said, there is no experiment or observation which could distiguish what was "Real" and what was "Apparent" weight, without invoking the Earth as an absolute frame of reference.
Yes I used the term "Net force". But a net force of zero has the same physical results as a force of zero, net or otherwise.
All fair comment. I would point at that, in most technical discussions, ISO values are usually the ones used. By THAT definition, what you refer to as "Apparent weight" would simply be "Weight".
As I'v said, there is no experiment or observation which could distiguish what was "Real" and what was "Apparent" weight, without invoking the Earth as an absolute frame of reference.
Yes I used the term "Net force". But a net force of zero has the same physical results as a force of zero, net or otherwise.
Join Date: Jun 2010
Location: Canada
Age: 37
Posts: 382
Likes: 0
Received 0 Likes
on
0 Posts
All fair comment. I would point at that, in most technical discussions, ISO values are usually the ones used. By THAT definition, what you refer to as "Apparent weight" would simply be "Weight".
The weight of a body in a specified reference system is that force which, when applied to the body, would give it an acceleration equal to the local acceleration of free fall in that reference system.
Capt Pit Bull:
Weight constant in a banked turn?
Deleted. Wizofoz had already addressed that. Sorry.
Weight constant in a banked turn?
Deleted. Wizofoz had already addressed that. Sorry.
Join Date: May 2009
Location: UK
Age: 41
Posts: 39
Likes: 0
Received 0 Likes
on
0 Posts
Not pilot but:
1. The Moon-Earth's two-body system center is below the surface of the Earth (I don't argue the tides explanation, but the barycenter is below the surface of the earth)
2. A force can do various things to objects, not only accelerate them. It can deform them. Your passenger door in differential pressure is deformed. You are probably thinking of kinematics and dynamics of rigid bodies which is excellent for the initial question.
Your wing flexes up during level flight even though there is no force unbalance, lift deforms your wing.
When I was in high school, 'force' was defined as 'the reason to alter the motion or shape of a body' (dodgy translation, but you get what I mean!).
When a train passes over a coin, the coins turns to foil. No (rigid body) acceleration involved.
Cheers!!
1. The Moon-Earth's two-body system center is below the surface of the Earth (I don't argue the tides explanation, but the barycenter is below the surface of the earth)
2. A force can do various things to objects, not only accelerate them. It can deform them. Your passenger door in differential pressure is deformed. You are probably thinking of kinematics and dynamics of rigid bodies which is excellent for the initial question.
Your wing flexes up during level flight even though there is no force unbalance, lift deforms your wing.
When I was in high school, 'force' was defined as 'the reason to alter the motion or shape of a body' (dodgy translation, but you get what I mean!).
When a train passes over a coin, the coins turns to foil. No (rigid body) acceleration involved.
Cheers!!
The reference system for "apparent weight" and "weight" are different. Apparent weight is measured from a non-inertial reference system. Weight is measured from an inertial reference system. Note the definition says "specified" reference system.
Where in that description does it use the term "Apparent weight" or specify that the frame of reference must be inertial? Once again let me ask- what would you use to measure weight that would distinguish between "Real" and "Apparent" weight?
Join Date: Jun 2010
Location: Canada
Age: 37
Posts: 382
Likes: 0
Received 0 Likes
on
0 Posts
Wiz.. you're hard to reason with!
It doesn't say apparent weight in the definition and it never says you have to be in an inertial reference frame... and I didn't say that either!
Apparent weight is in the non-inertial reference system and weight is in the inertial reference system. I'm just saying what it is! Go look it up.
Where in that description does it use the term "Apparent weight" or specify that the frame of reference must be inertial? Once again let me ask- what would you use to measure weight that would distinguish between "Real" and "Apparent" weight?
Apparent weight is in the non-inertial reference system and weight is in the inertial reference system. I'm just saying what it is! Go look it up.
Join Date: Sep 2000
Location: Bielefeld, Germany
Posts: 955
Likes: 0
Received 0 Likes
on
0 Posts
I cut out of this discussion because it was no longer fun.
It is fun to use some physics, indeed to hint to people that they weigh a quarter of a kilo less at the poles than they do at the equator, for example, but it is not fun to deal with silliness such as
by someone who doesn't appear to understand the difference between a question and an assertion.
Wizofoz is a phenomenalist about physical science. That is, he correctly observes that equations are symmetric and that no one side is preferred to the other, but he concludes that this is all that can be said. Not so. I mention a couple of features of causality, and he claims not to know what I mean.
Causality is an important concept, determination of which is probably the main activity in explaining accidents, which people in commercial aviation generally consider a very important activity. And indeed which demonstrably confuses lots of people (including, unfortunately, some accident investigators). So one cannot dismiss it. Wizofoz is right to point out that it plays no role in, say, calculations in Newtonian dynamics, but that might prompt him, and others, as it prompted Kant, to wonder why not.
PBL
It is fun to use some physics, indeed to hint to people that they weigh a quarter of a kilo less at the poles than they do at the equator, for example, but it is not fun to deal with silliness such as
...PBL is wrong about what his scales will read as he does not appear to understand the concept that angular velocity has an absolute value, and therefore is present in any inertial frame of reference.
Wizofoz is a phenomenalist about physical science. That is, he correctly observes that equations are symmetric and that no one side is preferred to the other, but he concludes that this is all that can be said. Not so. I mention a couple of features of causality, and he claims not to know what I mean.
Causality is an important concept, determination of which is probably the main activity in explaining accidents, which people in commercial aviation generally consider a very important activity. And indeed which demonstrably confuses lots of people (including, unfortunately, some accident investigators). So one cannot dismiss it. Wizofoz is right to point out that it plays no role in, say, calculations in Newtonian dynamics, but that might prompt him, and others, as it prompted Kant, to wonder why not.
PBL
Join Date: Aug 1999
Location: England
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
Oh my.
Look away for a couple of days and a year old thread gets necroed and gains a couple of pages.
I really don't want to get into it again, so many things being talked about and so many red herrings. There's about 8 different discussions underway. Stop reading if you're of a nervous disposition.
Here are a few random thoughts:
1. Forget about the ISO and start reading Physics textbooks. Since when did international non government organisations know bugger all about anything?
2. An equation is equally correct however you express it, and causality should not be inferred. However, as an aide-memoire, there are a great many basic physical relationships that lend themselves to being expressed as Effect = Cause / Opposition, and therefore purely as a convenience it can be a useful route to memorisation to express a relationship in a particular way.
3. cwatters. Sorry mate, that's bollox. How you think a climb can be analysed by ignoring thrust is so far out there I'm gobsmacked. Do yourself a favor and analyse the forces parallel to and perpendicular to the flight path instead of vertically and hrizontally before my eyes start bleeding and my head implodes.
<incoherently grumpy>
Look away for a couple of days and a year old thread gets necroed and gains a couple of pages.
I really don't want to get into it again, so many things being talked about and so many red herrings. There's about 8 different discussions underway. Stop reading if you're of a nervous disposition.
Here are a few random thoughts:
1. Forget about the ISO and start reading Physics textbooks. Since when did international non government organisations know bugger all about anything?
2. An equation is equally correct however you express it, and causality should not be inferred. However, as an aide-memoire, there are a great many basic physical relationships that lend themselves to being expressed as Effect = Cause / Opposition, and therefore purely as a convenience it can be a useful route to memorisation to express a relationship in a particular way.
3. cwatters. Sorry mate, that's bollox. How you think a climb can be analysed by ignoring thrust is so far out there I'm gobsmacked. Do yourself a favor and analyse the forces parallel to and perpendicular to the flight path instead of vertically and hrizontally before my eyes start bleeding and my head implodes.
<incoherently grumpy>
Join Date: Dec 2001
Location: England
Posts: 1,389
Likes: 0
Received 0 Likes
on
0 Posts
> Do yourself a favor and analyse the forces parallel to and perpendicular to
> the flight path instead of vertically and hrizontally
You're right of course...
Lift + weight*cos(climb angle) = 0
so
Lift = - weight*cos(climb angle)
Since cos(any angle) < 1
Lift < weight.
I'll delete my earlier post.
> the flight path instead of vertically and hrizontally
You're right of course...
Lift + weight*cos(climb angle) = 0
so
Lift = - weight*cos(climb angle)
Since cos(any angle) < 1
Lift < weight.
I'll delete my earlier post.
Hi CBP,
My point on weight remains this- What instrument would you use to determine whether weight is "Real" or "Apparent"? If you can't differentiate between the two, are they not the same thing?
You earlier brought up the idea that an observer on the Earths surface could determine which part of the aircrafts weight was due to Gravity, and which to acceleration. True, but this gives the Earths surface a privileged frame of reference.
Take an observer in freefall- from HIS POV, ALL the force on the aircraft would be due to it's acceleration, NONE due to Gravity (as from his frame of reference, there isn't any). The Aircrafts acceleration is absolute. Which part is "Real" and which is "Apparent" is relative.
I understand what you are saying about Causality, but still think it doesn't apply- Take a meteor striking the Earth- It undergoes an acceleration. Has a force caused the mass to accelerate, or has it's acceleration caused a force? My answer is "It's the same thing, as they are EQUIVALENT
PBL,
Several posts by you since I explained you were in error regarding rotation. It exists (as does it's effect) in any frame of reference. Do you acknowledge this?
ETA,
Actually PBL, reading your last reply to me- Are you saying you DO agree about rotation, and that your statement that implied rotation was relative was a red herring?
I'm sorry, but you write in riddles. I'd appreciate a clear explanation of your understanding of this.
My point on weight remains this- What instrument would you use to determine whether weight is "Real" or "Apparent"? If you can't differentiate between the two, are they not the same thing?
You earlier brought up the idea that an observer on the Earths surface could determine which part of the aircrafts weight was due to Gravity, and which to acceleration. True, but this gives the Earths surface a privileged frame of reference.
Take an observer in freefall- from HIS POV, ALL the force on the aircraft would be due to it's acceleration, NONE due to Gravity (as from his frame of reference, there isn't any). The Aircrafts acceleration is absolute. Which part is "Real" and which is "Apparent" is relative.
I understand what you are saying about Causality, but still think it doesn't apply- Take a meteor striking the Earth- It undergoes an acceleration. Has a force caused the mass to accelerate, or has it's acceleration caused a force? My answer is "It's the same thing, as they are EQUIVALENT
PBL,
Several posts by you since I explained you were in error regarding rotation. It exists (as does it's effect) in any frame of reference. Do you acknowledge this?
ETA,
Actually PBL, reading your last reply to me- Are you saying you DO agree about rotation, and that your statement that implied rotation was relative was a red herring?
I'm sorry, but you write in riddles. I'd appreciate a clear explanation of your understanding of this.
Last edited by Wizofoz; 4th Jul 2010 at 07:19.
Join Date: Sep 2000
Location: Bielefeld, Germany
Posts: 955
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by Wizofoz
My point on weight remains this- What instrument would you use to determine whether weight is "Real" or "Apparent"? If you can't differentiate between the two, are they not the same thing?
Originally Posted by Wizofoz
I understand what you are saying about Causality, but still think it doesn't apply- Take a meteor striking the Earth- It undergoes an acceleration. Has a force caused the mass to accelerate, or has it's acceleration caused a force? My answer is "It's the same thing, as they are EQUIVALENT
Originally Posted by Wizofoz
Several posts by you since I explained you were in error regarding rotation. It exists (as does it's effect) in any frame of reference. Do you acknowledge this? ..........
I'm sorry, but you write in riddles. I'd appreciate a clear explanation of your understanding of this.
I'm sorry, but you write in riddles. I'd appreciate a clear explanation of your understanding of this.
PBL