A little help? Sol I? Dan O? Anyone???

[RossFW]

Hi guys,

I need some help from a physics Guru, even if it is to tell me I'm wrong so I can drop it.

On an Aviation forum, a discussion came up regarding the forces on an aircraft in a turn.

As you'd be aware, and aircraft in a 60deg Angle of Bank turn experiences 2g. People started refering to this as the Aircrafts "Apparent Weight".

I chimed in and said it was meaningless calling it "Apparent Weight" as it was indestiguishable from "Real" weght. Basically the the opposite force felt as a reault of the aircrafts acceleration was the same thing as that due to Gravity, so it was incorrect to label them as different things.

I got pretty soundly shouted down, and one posted invoked that I was using "Operationalsim" which was out-moded.

What are the physics heavy-weights opinions?

Thanks

 

[erlando]

I'm not pretending to be a physics heavyweight anywhere near Mr. Invictus. But anyway..

"Weight" is a gravitational force. So if the apparent gravitational force doubles it stands to reason that the "apparent weight" doubles. Just as well as the weight of an object on the Moon is only 1/6th of the weight of the same object on Earth. Of course the mass stays the same.

 

[Ivor the Engineer]

I (and silly old harry) agree with the op. However, is this just an argument over the use of terminology?

 

[RossFW]

I (and silly old harry) agree with the op. However, is this just an argument over the use of terminology?

No, not just terminology. They insisted that the component of weight due to acceleration was "Different" to that caused by Gravity, and that I didn't understand causation.

 

[X]

It has more to do with the components/sources of the forces than with what is felt, IMHO.

Weight, as Erlando mentioned, is fairly specific in being due to gravity.

The phrase "apparent weight" makes concessions to what is felt, but also makes it clear that it only appears to be weight (i.e. gravity-based) when the actual breakdown contains the force-due-to-gravity (weight) and the force due to acceleration.

 

[sol invictus]

No, not just terminology. They insisted that the component of weight due to acceleration was "Different" to that caused by Gravity, and that I didn't understand causation.

There's a deep principle of physics - the equivalence principle - which says you're right. Inside a sufficiently small laboratory, you cannot tell whether you're in a gravitational field ("sufficiently small" means too small to measure tidal effects). If you feel an acceleration it could be because you're in a room or plane that's being supported against the force of gravity by the ground or air, or because the room or plane is accelerating in zero gravity due to something else (like an elevator cable or a banked turn), or some combination of the two as in your example.

Of course you could also just look out the window and observe you're flying over earth, and use your knowledge of its mass to determine which component of your weight is "real" and which is "apparent". But I suppose you consider that cheating.

ps - I'm not sure what "operationalism" is, but I think I believe in it.

 

[RossFW]

Thanks Sol, can I quote you?

And, just so I can cheat and deliver an argumant from Authority, could you give me a quite precise of your qualifications?

 

[Crossbow]

Hi guys,

I need some help from a physics Guru, even if it is to tell me I'm wrong so I can drop it.

On an Aviation forum, a discussion came up regarding the forces on an aircraft in a turn.

As you'd be aware, and aircraft in a 60deg Angle of Bank turn experiences 2g. People started refering to this as the Aircrafts "Apparent Weight".

I chimed in and said it was meaningless calling it "Apparent Weight" as it was indestiguishable from "Real" weght. Basically the the opposite force felt as a reault of the aircrafts acceleration was the same thing as that due to Gravity, so it was incorrect to label them as different things.

I got pretty soundly shouted down, and one posted invoked that I was using "Operationalsim" which was out-moded.

What are the physics heavy-weights opinions?

Thanks

While I do see what you are driving at, and I can see what the others are driving at, but strictly speaking, everyone is wrong.

To explain, the correct term is "load factor" which is the ratio between total airload acting on the airplane to gross weight of the airplane.

And if anyone want to complain about that term, then they need to consult the Pilots Handbook of Aeronautical Knowledge and explain to the FAA that they have it wrong as well.

 

[jasonpatterson]

Unless they were trying to compare forces on various parts of the airplane (differentiating between what the tips of the wings felt vs the fuselage, for instance) you're right, more or less. It doesn't sound like this was their intent.

You're entirely correct in saying that the forces are completely indistinguishable from one another, regardless of their source. Depending on the problem you're working with, it might be entirely appropriate to call the net force on the person his or her weight. It might also be confusing to do so, if not wrong (after all, we can call any force anything we like.)

From what I've seen, weight corresponds to the reading on a scale placed between an object and the surface on which it rests (the opposite of the normal force, in other words.) If I'm in an elevator accelerating downward, my weight decreases, if I'm on an elevator accelerating upward, my weight increases. If I get into the Gravitron ride at the fair the centripetal force from the wall keeping me spinning in a circle provides my weight and gravity and friction don't really play a part (as they are acting parallel to the surface in question.)

I guess what I'm trying to say is that weight has a common definition, and if the net force you're asking about doesn't involve squashing a person against something else, then it would be confusing to call it his or her weight. They do call it an apparent weight though, so it seems likely that you are entirely in the clear.

More simply, if your question is whether there are cases where weight is due to something other than gravity alone, then the answer is definitely yes.

 

[jasonpatterson]

And if anyone want to complain about that term, then they need to consult the Pilots Handbook of Aeronautical Knowledge and explain to the FAA that they have it wrong as well.

There's nothing wrong with giving a specific name to a commonly occurring force, but that doesn't make that force special in any way, whether the FAA likes it or not.

 

[jasonpatterson]

No, not just terminology. They insisted that the component of weight due to acceleration was "Different" to that caused by Gravity, and that I didn't understand causation.

Bah humbug, this is what happens when you walk away to make lunch while typing out a response... I have to wonder, how does your supposed lack of understanding of forces have anything to do with causation?

 

[Modified]

How could 2g be an "apparent weight" for an aircraft? It would be the "apparent gravitational force" inside, if anything.

I wouldn't have a problem if the scale weights of passengers in the plane were described as "apparent weights".

 

[erlando]

No, not just terminology. They insisted that the component of weight due to acceleration was "Different" to that caused by Gravity, and that I didn't understand causation.

That's just silly. There's nothing special about any of the forces constituting the "apparent weight".

Also I agree with Modified. It's almost meaningless to talk about the "apparent weight" of the aircraft. The passengers inside is a different matter.

 

[RossFW]

The reason the "Apparent Weight" of the aircraft is important is because that's how much lift the wing has to produce in order to keep the aeroplane at a constant altitude.

Thus if you put the aircraft under a load and increase it's weight, you either have to incrase speed (limited by available thrust) or inrease angle of attack (Which has an upper limit- clmax,beyond which the wing stalls.)

 

[rwguinn]

How could 2g be an "apparent weight" for an aircraft? It would be the "apparent gravitational force" inside, if anything.

I wouldn't have a problem if the scale weights of passengers in the plane were described as "apparent weights".

The reason the "Apparent Weight" of the aircraft is important is because that's how much lift the wing has to produce in order to keep the aeroplane at a constant altitude.

Thus if you put the aircraft under a load and increase it's weight, you either have to incrase speed (limited by available thrust) or inrease angle of attack (Which has an upper limit- clmax,beyond which the wing stalls.)

What RossFW said.
It's a real force, and aerodynamics and loads have to account for it.

 

[RossFW]

Bah humbug, this is what happens when you walk away to make lunch while typing out a response... I have to wonder, how does your supposed lack of understanding of forces have anything to do with causation?

Well, I copped a speil and a link to a philosophical document, and was told

The view of science that quantities which you cannot discriminate with instruments are the same thing is about the only philosophy of physics which has been definitively discredited in the last hundred years. So it is rather inappropriate to try it on here, don't you think?"

I didn't understand what he meant...

 

[jasonpatterson]

Wow, if I'm understanding what he wrote, he's basically saying that the equivalence principle, which Sol wrote about earlier, is wrong. The equivalence principle doesn't have much to do with causation (A occurs because of B) in any direct way, but it's one of the founding ideas of general relativity and has been verified to the extent that GR has been (extensively, to say the least.)

 

[Modified]

The reason the "Apparent Weight" of the aircraft is important is because that's how much lift the wing has to produce in order to keep the aeroplane at a constant altitude.

In the OP you seem to be saying that people were referring to 2g as the apparent weight. Perhaps that is not what you meant. The apparent weight, if we are to accept the term, would be twice the ground weight.

 

[sol invictus]

Thanks Sol, can I quote you?

Sure.

And, just so I can cheat and deliver an argumant from Authority, could you give me a quite precise of your qualifications?

I'd rather not. Let's just say I'm qualified.

Well, I copped a speil and a link to a philosophical document, and was told

The view of science that quantities which you cannot discriminate with instruments are the same thing is about the only philosophy of physics which has been definitively discredited in the last hundred years. So it is rather inappropriate to try it on here, don't you think?

I didn't understand what he meant...

Insofar as I can parse that, I disagree with it completely. The idea that the only real things are those we can (in principle) measure not only has not been discredited, it's one of the most powerful ideas around. It has repeatedly proven its worth over the last century (the equivalence principle being an excellent example).

 

[Vorpal]

He seems to be basically saying that the use of Ockham's razor in physics has been been "definitively discredited." This makes even less sense.