Brain Teasers

Re: Brain Teasers

PostBy: Devil505 On: Sat Aug 09, 2008 12:25 pm

Freddy wrote:stall the engines, let the airplane fall, the passengers are now weightless, just like the astronauts. The reason the astronauts seem weightless is because they are falling......fallling around the Earth, they just happen to fall at the same rate of speed that the curve of the Earth has.



You should have know you weren't going to get off that easy! :lol:

If they seem weightless because they are "falling" around the Earth, then why are they still weightless when they are on their way to & from the moon, & thus not falling around the Earth?
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Re: Brain Teasers

PostBy: Devil505 On: Sat Aug 09, 2008 1:41 pm

Maybe Freddy has already left so the question is open to anyone.
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Re: Brain Teasers

PostBy: gaw On: Sat Aug 09, 2008 9:05 pm

Devil5052 wrote:If they seem weightless because they are "falling" around the Earth, then why are they still weightless when they are on their way to & from the moon, & thus not falling around the Earth?

They are falling in love, space is a lonely place so if you can't be with the one you love, love the one your with. :gee:
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Re: Brain Teasers

PostBy: LsFarm On: Sun Aug 10, 2008 10:10 am

The answer to the bird flying inside the airplane is bunk.. The weight of the bird does not leave the vessel. it cannot become zero. If so, where did the weight go??? If the air in the airplane supports the flying bird then the weight of the air increases by the weight of the bird.

I don't care what some egghead in a univeristy says.. if the plane weighs X, it weighs X. If the bird decides to fly and hover above it's perch, then the weight of the air in the airplane has increased by the weight of the bird. The weight can't go away. It has to be accounted somehow..This is if the bird is flying, or hovering.

NOW Try this one... If you have an airplane in the air, with 100 gymnasts all hanging from the ceiling. The plane weighs X plus the passengers P.. so the lift of the wings is supporting X+P. So if all 100 gynasts let go of their overhead bars and drop to the floor.. lets say it takes 2 seconds [irrelevant] for the gymansts to land on the floor...

OK, during the above situation, does the airplane Weigh X+P while the gymnasts are dropping to the floor, but NOT yet touching the floor?? Or does the airplane weigh just X ??

Greg L
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Re: Brain Teasers

PostBy: coaledsweat On: Sun Aug 10, 2008 11:27 am

A flying airplane weighs nothing. :)
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Re: Brain Teasers

PostBy: Devil505 On: Sun Aug 10, 2008 11:29 am

LsFarm wrote:If the bird decides to fly and hover above it's perch, then the weight of the air in the airplane has increased by the weight of the bird. The weight can't go away. It has to be accounted somehow..This is if the bird is flying, or hovering.



I'll stick with the MIT Physics dept answer for this reason:

Once the bird is flying, its weight is counteracted by the lift it's wings are producing. (bird weighs 2 ounces & the bird's wings are creating 2 ounces of lift) Thus, the bird's weight is not added to the weight of the air in the cabin, but is negated by the lift of it's wings.

(now you can see where a heated debate over this was only ended by a call to MIT! :lol: )


LsFarm wrote:NOW Try this one... I


I don't have time right now but I'll tackle that one later. :devil:
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Re: Brain Teasers

PostBy: Steve.N On: Sun Aug 10, 2008 11:39 am

I would say that the aircraft weighs just X. When they are hanging the aircraft has to overcome the force of gravity acting on the gymnasts but when they drop, for that instant, the aircraft is not overcoming gravity acting on the gymnasts.
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Re: Brain Teasers

PostBy: Steve.N On: Sun Aug 10, 2008 12:08 pm

Here is a whole discussion on the bird in the airplane question on a physics site.

They agree with Greg and I

http://www.physforum.com/index.php?showtopic=7381
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Re: Brain Teasers

PostBy: Devil505 On: Sun Aug 10, 2008 1:04 pm

Steve.N wrote:Here is a whole discussion on the bird in the airplane question on a physics site.

They agree with Greg and I

http://www.physforum.com/index.php?showtopic=7381


While I didn't have time to read all the responses, it appears to be just a layman's discussion of the possibilities. I'll still go by the MIT physics professor's answer. If anyone cares to contact an expert in this field, please post their response. (interesting problem though, eh?)


Edit: Let' try thinking about this problem from another perspective:

A 200 lb man is standing on the ground on a scale.
He jumps into the air & his weight is now measured at -0- lbs (electronically)

Where did his weight go?

I say it simply disappeared, negated by the force of his leg muscles propelling him into the air & was not somehow transfered to the air itself.

In a similar way, the bird's weight is no longer present (temporarily while it's in flight) as it is counteracted the lift created by its wings)




Or Another Example:



A rocket sits on the ground weighing 2000lbs
When its engines fire they create 2500lbs of thrust
The rocket start to lift off, but its weight is not simply pressing down against the ground or air via its exhaust since the rocket works just the same in the empty vacuum of space. (It's Newton's Third Law of Motion.....For every action, there is an equal & opposite reaction)

Therefore, the weight is not transfered, it simply disappears as a measurable force, according to Newton's third law of motion




That took allot out of me....I need a nap! :devil:
Last edited by Devil505 on Sun Aug 10, 2008 3:31 pm, edited 2 times in total.
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Re: Brain Teasers

PostBy: Devil505 On: Sun Aug 10, 2008 2:58 pm

LsFarm wrote:OK, during the above situation, does the airplane Weigh X+P while the gymnasts are dropping to the floor, but NOT yet touching the floor?? Or does the airplane weigh just X ??



Just X since the gymnasts weight is no longer pressing down or being resisted by anything.
(Think of it this way: Weight is only a measure of the force that a mass exerts when it is resisted as it tries to accelerate towards the center of the gravitational field....The Earth in this case)
In reality, weight has no actual substance or mathematical value....It is just a "word" we made up to describe the measurement of the resistance a body exerts in a gravitational field when prevented from accelerating towards the center. The more the mass, the more the measurable resistance or...what we call "weight."
Take away the resistance & you take away the "weight".


My brain hurts! :lol:
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Re: Brain Teasers

PostBy: LsFarm On: Sun Aug 10, 2008 3:27 pm

Devil, you answered my question: the weight of the guy who jumps in the air is zero because he is falling, nothing is supporting him.. but the bird in the airplane is flying, and the air in the plane is supporting him, hence the weight of the plane is still plane+bird..

The answer to my posed question is that the plane for ~2 seconds weighs just X. the air in the airplane is not supporting the people falling..

Greg L
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Re: Brain Teasers

PostBy: Devil505 On: Sun Aug 10, 2008 3:38 pm

LsFarm wrote:but the bird in the airplane is flying, and the air in the plane is supporting him, hence the weight of the plane is still plane+bird..



I'll have to think about that Greg. Is the air really supporting the bird ,in flight....or is it a factor of lift itself somehow involving Newton's Third Law of Motion? (Lower air pressure on the top of the wing in effect "sucking" the wing upwards, or Lift?)

If you thesis is correct, is a rocket being somehow supported in it's flight through the atmosphere?

whoa.....My brain is realy turning to mush!! :lol:
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Re: Brain Teasers

PostBy: LsFarm On: Sun Aug 10, 2008 3:46 pm

Nope, the rocket is pushed into orbit by thrust, action/reaction. ONce in orbit it is constantly 'falling to earth' . given the right speed and orbit, it never reaches earth and constantly orbit..

Greg L.

.
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Re: Brain Teasers

PostBy: Devil505 On: Sun Aug 10, 2008 8:00 pm

LsFarm wrote:Nope, the rocket is pushed into orbit by thrust, action/reaction. ONce in orbit it is constantly 'falling to earth' . given the right speed and orbit, it never reaches earth and constantly orbit..



So, why are astronauts still weightless in their spacecraft when they are not falling around the Earth? (say when they are going to or from the Moon)
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Re: Brain Teasers

PostBy: charlie On: Sun Aug 10, 2008 8:06 pm

Sooooooo..... if something is falling or flying, it has no weight? That would mean we could cure obesity by getting people to levitate rather than a more difficult change to their diets and exercise routine???
Is it really weightlessness or our inability to accurately measure or gravity or pressure? (Lost my copy of the Principia)
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