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Author Topic: Question of the Week - Old Version  (Read 179326 times)

Offline bezoar

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Re: Question of the Week - Old Version
« Reply #100 on: 11/01/2004 03:42:28 »
Can they sense your breathing changes from another room?  If so, that would explain why my kids didn't begin sleeping all night until they were about 12 or 13.  I'm not much of a sleeper and awaken frequently during the night.  It would be interesting to study if babies who sleep all night long from the time they come home from the hospital have mother's who are heavy sleepers.

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #101 on: 15/01/2004 18:04:22 »
This was quite a tough question.

The answer probably lies in the fact that dreaming occurs when you are in a state of near-wakefulness. Events from the environment can therefore intrude into your dream and even participate in it. Everyone must have experienced the hilarious situation of talking to someone who is asleep. They have no recollection afterwards of what was said, unless they wake up mid conversation.

As to why you wake up and then hear the alarm, giving the impression that you pre-empted the alarm clock, I think there are many possible explanations. You could geuninely have woken up before the alarm because your body-clock has become accustomed to you getting up at that time that it woke you up automically. Alternatively, and this is the explanation I favour, you were dreaming when the alarm went off. In that split second the alarm got incorporated into your dream. As our sense of time is totally skewed when we dream you have no concept of when you really woke up, and when the alarm really started going off.

A hard nut to crack, but still a great question.

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #102 on: 15/01/2004 18:05:48 »
THIS WEEK'S QOTW :

"IF ALL THE PASSENGERS ON AN AEROPLANE SUDDENLY JUMPED INTO THE AIR AT THE SAME TIME, WOULD THE PLANE MOMENTARILY WEIGH LESS ?"

Have a go, below :

TNS
 

Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #103 on: 16/01/2004 07:42:18 »
That's just like a question that was on this old maths competition thing. the question was, there's a guy that's a juggler that wants to cross a bridge that can only hold a certain weight, and him and the bazlls weigh over it but him and one ball is enough to get by, the question was if he always has two balls in the air can he cross safely.

It does sound like one of those questions, I know the nswer is that it would weight exactly the same, but I'm not exactly sure why. Well the passengers are not 'the plane' so the plane would weigh the same, but I don't think that's really the issue. hmm. I'm sure it has a lot to do with the diagrams of vectors pointing all over the place that my physics teacher just loves drawing. I can just imagine one now ... there's be P pointing downwards from the middle of the plane, something pointing upwards for the thing that keeps the airplane up, lots of P's for the passengers' weights, and lots of R's pointing up for the reaction de support. But come to think of it, if you say 'would the plane momentarily weigh less" you probably mean the plane and the passengers' weights combined right? So on the ground it'd be the same but instead of the vector for the thing that keeps the plane in the air there'd be a big R for the reaction de support of the ground. and when the passengers jump, they'd have to, like, push on the plane a lot to get themselves up off the floor, so the diagram with them pushing off would be a vector pushing down for each, a vector pushing up that would carry them up, their weight, and their reaction de support. The diagram with them in the air would be with their weight and the vector pushing them up then on the way to the ground it would be just their weight. When they're on the floor just as they jump I suppose their reaction de support's would be bigger than before they pushed off. So, in conclusion, I suppose the combined weight would be bigger as they pushed off (but the R's bigger so the plane doesn't, like, move underground or whatever) then the P would just be of the plane, then when they land it'd be the same again except maybe that the landing of the passengers would induce some movement of the plane and make the combined weight go up again for a short time until the movement of the passengers towards the earth had stopped, by the R's going upwards?

I don't know if that's how it's meant to be answerd but that's just a try.

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Offline cuso4

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Re: Question of the Week - Old Version
« Reply #104 on: 16/01/2004 08:42:27 »
At the instant when all the feet of the passengers leave the floor of the aeroplane, the overall reaction  should decrease but then all the passengers are still experiencing gravitational pull so the overall weight shouldn't change.

Not the most straight forward question, I'll have to think about it again.

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #105 on: 16/01/2004 15:02:31 »
what do you mean by 'the overall reaction will decrease'? with the gravitational pull, it's giving them acceleration back towards the plane, but it is only applied to the passengers while they're in the air, not to the plane right? Please tell us the answer NS!

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Offline tweener

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Re: Question of the Week - Old Version
« Reply #106 on: 16/01/2004 19:45:28 »
Last night I wrote a long response to this and my computer crashed before I got it submitted.  Here is a short version.

The average weight of the plane and passengers, averaged over the whole "jump" would remain constant.  On a finer timescale: The weight would start as the combined weight of the plane and passengers. Then, as they jumped, the "weight" would increase to accelerate them upward.  While they were off the floor of the plane the weight would decrease to just the weight of the plane. Then, when they hit the floor of the plane the weight would again increase a lot to decelerate them. Finally, the weight would come back to the "normal" weight of the plane and passengers after they got back to the floor.


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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #107 on: 17/01/2004 08:58:00 »
whoo!

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Offline notnakeeinappalachee

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Re: Question of the Week - Old Version
« Reply #108 on: 21/01/2004 14:57:15 »
The plane weighs the same.  The weight of the plane plus its contents, however, is greater when its contents are in contact with its floor.  

 

Offline chris

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Re: Question of the Week - Old Version
« Reply #109 on: 21/01/2004 16:54:42 »
But what about the fact that the plane is sealed (pressurised) - does this make a difference ?

Chris

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Offline bezoar

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Re: Question of the Week - Old Version
« Reply #110 on: 22/01/2004 21:58:17 »
Shouldn't the pressurization of the plane, in itself, increase the weight?
 

Offline tweener

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Re: Question of the Week - Old Version
« Reply #111 on: 23/01/2004 05:24:34 »
The overpressure of the air would increase the weight a little.  Probably a few milligrams for the amount of pressure in a plane.  Of course it depends on the size of the plane.


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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #112 on: 26/01/2004 12:42:03 »
ANSWER TO "WHAT HAPPENS TO THE WEIGHT OF A PLANE IF ALL OF THE PASSENGERS JUMP INTO THE AIR SIMULTANEOUSLY ?"

This was a tough one. Tweener's answer is correct in that in order to accelerate themselves off the floor of the plane the passengers must apply a force and hence the plane will transiently increase in weight. Whilst the passengers are airbourne their weight is no longer pushing down on the plane so it rebounds upwards. Then as they land again their weight is added to that of the plane and the total masss returns to the starting value.

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #113 on: 26/01/2004 13:26:21 »
Here's this weeks QOTW :

"HOW FAST IS THE EARTH SPINNING ON ITS AXIS ? HAS IT ALWAYS TURNED THIS FAST ?"

TNS
 

Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #114 on: 26/01/2004 15:11:25 »
I have no idea how fast, but I remember the teacher saying in astronomy three years ago that it spun really fast when it was formed and is slowing down.

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #115 on: 26/01/2004 15:12:09 »
I have no idea how fast, but I remember the teacher saying in astronomy three years ago that it spun really fast when it was formed and is slowing down.

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Offline Donnah

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Re: Question of the Week - Old Version
« Reply #116 on: 26/01/2004 20:54:00 »
According to Gregg Braden the earth's magnetics are decreasing and frequency is increasing.

Not sure about how fast the earth is spinning, but guess you could work it out using the circumference of the planet and a 24 hour time period.
 

Offline roberth

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Re: Question of the Week - Old Version
« Reply #117 on: 27/01/2004 02:31:00 »
Earth currently rotates at about 1,609 km/h. I don't know if this is constant.
« Last Edit: 27/01/2004 02:51:13 by roberth »
 

Offline notnakeeinappalachee

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Re: Question of the Week - Old Version
« Reply #118 on: 27/01/2004 16:40:38 »
Pertaining to the last question--weight is due to gravity, which is the force of attraction exerted by the mass of two bodies.  In the case of the airplane, the two bodies are the plane and the earth.  The slight increase in earthward force (and acceleration) exerted when the people push downward in order to jump is not due to the pull exerted by earth and therefore is not an element in the plane's weight.  

Never was much for angular momentum and its relatives.
 

Offline chris

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Re: Question of the Week - Old Version
« Reply #119 on: 27/01/2004 22:53:37 »
I think that's what they are getting at by referring to "pedants" - it is assumed for the sake of simplicity that the word "plane" refers to the entire system i.e. the plane, the air it contains, and the passengers.

Anyway, what abou this earth rotation question ?

Chris

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Offline bezoar

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Re: Question of the Week - Old Version
« Reply #120 on: 28/01/2004 02:52:20 »
How fast the earth spins might depend on where on earth you are.
 

Offline roberth

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Re: Question of the Week - Old Version
« Reply #121 on: 29/01/2004 00:33:01 »
OK, then, 1,609 km/h at the equator.
 

Offline pipster

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Re: Question of the Week - Old Version
« Reply #122 on: 02/02/2004 14:57:22 »
The earth and all the other planets in the solar system are spinning because of the resultant angular momentum from their formation billions of years ago. As the clouds of dust and gas came together under gravity, the matter they contained was pulled in closer and closer until finally the planet we now live on was formed.
Just as when an ice skater spinning on the spot goes faster when they pull their arms in (try it on a swivel chair) this gas contraction increased the angular momentum that causes our days and nights to come round every 12 hours (at the equinox).

Like all systems, energy is lost over time (like a pendulum eventually comes to rest vertically) and so the rotation about our axis is decreasing. This will eventually increase the length of the day since more time will be spent in or out of sunlight at anytime.

Velocity of rotation of a point about an axis (in this case angular momentum) = 2xpixr/24hours
At the north pole where the distance to the centre of rotation could be close to zero, you will have zero angular momentum and it increases up to the equator.

IF the earth spinning around on its axis slows down enough, days will get longer and longer and eventually the length of a day might over take the length of the year, which I believe is what has happened to Mercury?
 

Offline Ultima

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Re: Question of the Week - Old Version
« Reply #123 on: 06/02/2004 12:54:21 »
The Earth wobbles on its axis wouldn't this effect the speed a tiny bit?
« Last Edit: 06/02/2004 12:58:37 by Ultima »
 

Offline roberth

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Re: Question of the Week - Old Version
« Reply #124 on: 09/02/2004 00:25:15 »
C'mon TNS. You should rename this topic "question of the fortnight".
 

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Re: Question of the Week - Old Version
« Reply #124 on: 09/02/2004 00:25:15 »

 

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