Cal Weldon said:
Ok I was just eating dinner and had the same feeling. Oh NOOO!!!! It gets even worse than I'd previously considered.
Any forward movement of the wheels of the jet (excluding anything due to forces external to the jet .... towing etc) is directly and exclusively due to the jet moving forward (the wheels aren't powered in and of themselves). If the jet can't move forward then the wheels can't move.
So I see 2 remaining possibilities.
1. The jet stands still with jets going full throtle and nothing moves not even the wheels.
2. The jet continually tries to get moving but as soon as it tries, the wheels spin faster and faster (as does the belt) and due to the lack of losses in the belt, the wheels and belt quickly accelerate to the point where the tyres fail and the jet crashes.
This just never seems to end....... Sigh......
wintermute said:
An externally hosted image should be here but it was not working when we last tested it.
AudioFreak said:
Oh, it gets even worse, you bet.
The jet can't even crash into the runway belt if the tires fail. As the wheels suddenly stop, so does the belt, so the jet can't even nose dive.
Now, if one tire were to blow, what would happen?
Max
Yes, the conveyer belt HAS to match the speed of the WHEELS. It doesn't say that the wheels has to be going the same speed as each other , just that the conveyer has to match them. It must be doing two different speeds at the same time.quickshift said:
Hi Guy's, I unsubcribed from this damn thread yesterday becuse my inbox was being saturated and my head hurt!!!!
Look
I'm back again!....It's a bl**dy addiction.....
Look
I'm back again!....It's a bl**dy addiction.....
AudioFreak said:
hehehehe yes I had the same thought quoted below.... but again it depends on the frame of reference and definitions of speed when I wrote that below the frame of reference was from outside the belt... 😉 Isn't it funny how something that at first seems so simple and obvious has so many finicky little details that can totally change your perspective!! 🙂
edit: the problem with this thread is that there are so many posts it is hard to read all other posts and we keep re-inventing the wheel (pun intended) <ducking>
Tony.
Lostcause said:Hi Guy's, I unsubcribed from this damn thread yesterday becuse my inbox was being saturated and my head hurt!!!!
Look
have you read all of the posts since you unsubscibed lost 😉
Tony.
wintermute said:
Every damn one.......can't help it...stop it....stop it!
"Its like a nightmare, it just keeps on getting worse"
or I think thats how it goes....
I think Zaphod beeble brox would have a hard time following this one!
Thinking about it..I bet Zaphod's heads would be in different camps.......now that would be confusing!
Yes please
Please actually read this it might be enlightening
or at least maybe help explain why the thread is still going.
OK I think it is time for a recap!!
I have attached the picture I put in my original post so that it is obvious which way I'm interpreting the motion of the belt and the wheel.
a. Unless the belt and the wheel have the same diameter it is not physically possible for them to have the same rotational speed. Clearly the length of the belt is much longer than the length of the circumference of the wheel so we have to assume that Match the speed of the wheel means something other than the rotational speed of the belt matches the rotational speed of the wheel.
b. So we can say as long as there is no slipping of the wheel or the belt then the surface speed of the belt and the wheel is matched.
now interestingly this means that even if the belt is stationary with respect to a viewpoint outside of the belt or wheel and the wheel is rolling forward (or backward) then the speed of the belt and the wheel (relative to each other) is still matched (as no slippage is occurring).
so IMO it all comes down to where you put your viewpoint (for gauging the speed of the belt and the wheel)
1. viewpoint is a fixed point on earth outside of the belt. from this viewpoint the only way the speed of the belt and the wheel can be matched, is if the belt is moving backward at the same rate that the centre of the wheel would be moving forward for a given rotation speed of the wheel (ie the plane remains stationary with repect to the viewpoint). otherwise the speed of the belt and the wheel relative to the observation point are not matched..... This scenario is impossible given the propulsion method ie the jet engine, as if the engine produces any forward movement then the rules of the question are broken. Secondly the belt cannot counteract the thrust of the engine, so in reality the plane would move forward, and the belt would continually increase speed to try and match the now faster moving wheel, the plane would continue to accelerate and so would the belt in a futile attempt to match the speed which it can't.
2. viewpoint is the centre of the wheel
three of possibilities here, probably more but 3 will do 😉
2.1 the plane starts to roll forward due to the thrust of the jets the belt doesn't move at all (relative to the earth) but relative to the centre of the wheel the belt moves away at a speed matching the rotational speed of the wheel (as defined above in b) The plane takes off and all aspects of the question have been fulfilled
2.2 the pilot puts on the breaks, the thrust of the engine pulls the plane and the belt forward. The wheel isn't rotating at all, the speed of the belt relative to the wheels reference point is 0 so they are matched, the plane takes off.
2.3 the plane starts moving forward and the wheels turn, the belt also starts to turn making the wheels rotational speed either increase or decrease depending on the direction the belt is turning. again as defined in b the speed of the belt and the wheel are matched and the plane will take off.
3. reference point on the belt.
As far as I can see with this one it is meaningless as the belt speed can never match the wheel speed as the belt from the reference point of the belt itself is stationary regardless of how it appears from any other reference point.
4. we don't take matching the speed of the wheel to mean as I defined in b, but to mean the speed of the wheel in a forward direction (ie the speed the centre of the wheel is travelling with respect to a fixed viewpoint outside of the belt.
all that has to happen here is if the wheel is moving forward at 10km/h then the belt has to move backward at 10Km/h for their speeds to be matched, the plane accelerates as normal taking off and the wheels spin at twice the speed they would normally.
There are probably other ways of interpreting this but I believe all of the above are valid interpretations of the question, and just go to show how bad the question is in the first place!!!!!
I suspect that this will continue 😉
edit: and I'm going to bed now 😉
Tony.
or at least maybe help explain why the thread is still going.
OK I think it is time for a recap!!
I have attached the picture I put in my original post so that it is obvious which way I'm interpreting the motion of the belt and the wheel.
a. Unless the belt and the wheel have the same diameter it is not physically possible for them to have the same rotational speed. Clearly the length of the belt is much longer than the length of the circumference of the wheel so we have to assume that Match the speed of the wheel means something other than the rotational speed of the belt matches the rotational speed of the wheel.
b. So we can say as long as there is no slipping of the wheel or the belt then the surface speed of the belt and the wheel is matched.
now interestingly this means that even if the belt is stationary with respect to a viewpoint outside of the belt or wheel and the wheel is rolling forward (or backward) then the speed of the belt and the wheel (relative to each other) is still matched (as no slippage is occurring).
so IMO it all comes down to where you put your viewpoint (for gauging the speed of the belt and the wheel)
1. viewpoint is a fixed point on earth outside of the belt. from this viewpoint the only way the speed of the belt and the wheel can be matched, is if the belt is moving backward at the same rate that the centre of the wheel would be moving forward for a given rotation speed of the wheel (ie the plane remains stationary with repect to the viewpoint). otherwise the speed of the belt and the wheel relative to the observation point are not matched..... This scenario is impossible given the propulsion method ie the jet engine, as if the engine produces any forward movement then the rules of the question are broken. Secondly the belt cannot counteract the thrust of the engine, so in reality the plane would move forward, and the belt would continually increase speed to try and match the now faster moving wheel, the plane would continue to accelerate and so would the belt in a futile attempt to match the speed which it can't.
2. viewpoint is the centre of the wheel
three of possibilities here, probably more but 3 will do 😉
2.1 the plane starts to roll forward due to the thrust of the jets the belt doesn't move at all (relative to the earth) but relative to the centre of the wheel the belt moves away at a speed matching the rotational speed of the wheel (as defined above in b) The plane takes off and all aspects of the question have been fulfilled
2.2 the pilot puts on the breaks, the thrust of the engine pulls the plane and the belt forward. The wheel isn't rotating at all, the speed of the belt relative to the wheels reference point is 0 so they are matched, the plane takes off.
2.3 the plane starts moving forward and the wheels turn, the belt also starts to turn making the wheels rotational speed either increase or decrease depending on the direction the belt is turning. again as defined in b the speed of the belt and the wheel are matched and the plane will take off.
3. reference point on the belt.
As far as I can see with this one it is meaningless as the belt speed can never match the wheel speed as the belt from the reference point of the belt itself is stationary regardless of how it appears from any other reference point.
4. we don't take matching the speed of the wheel to mean as I defined in b, but to mean the speed of the wheel in a forward direction (ie the speed the centre of the wheel is travelling with respect to a fixed viewpoint outside of the belt.
all that has to happen here is if the wheel is moving forward at 10km/h then the belt has to move backward at 10Km/h for their speeds to be matched, the plane accelerates as normal taking off and the wheels spin at twice the speed they would normally.
There are probably other ways of interpreting this but I believe all of the above are valid interpretations of the question, and just go to show how bad the question is in the first place!!!!!
I suspect that this will continue 😉
edit: and I'm going to bed now 😉
Tony.
Attachments
Wintermute...
Well that just about covers it so you can go and lie down in a dark room and listen to some nice soothing music now!
......and just confirm my beliefs...I dont believe you can answer the question either! Just too many variables....but
If forced to do so then I would still say that the wheels turn at 2x and the plane is gone...bye, bye........
........I think......
Lee
Well that just about covers it so you can go and lie down in a dark room and listen to some nice soothing music now!
......and just confirm my beliefs...I dont believe you can answer the question either! Just too many variables....but
If forced to do so then I would still say that the wheels turn at 2x and the plane is gone...bye, bye........
........I think......
Lee
I'll say it again.... According to the original question, if you aren't going to have any slippage or skidding, the surface speed of the wheel must equal the surface speed of the belt.
Wow, still going in earnest!
Try this. If the plane moves forward, the belt moves forward also. This stops the wheel rotation. Belt speed = wheel speed. We shall talk linear velocity for this argument.
If we increment time forward, the plane merrily takes off as the belt speeds forward with respect to the ground and the wheels not moving with respect to the belt. This is possible because the belt always moves to stop the wheel from rotating.
Does this work for anyone?
-Chris
No one has an answer to my previous question? (post 395)
Try this. If the plane moves forward, the belt moves forward also. This stops the wheel rotation. Belt speed = wheel speed. We shall talk linear velocity for this argument.
If we increment time forward, the plane merrily takes off as the belt speeds forward with respect to the ground and the wheels not moving with respect to the belt. This is possible because the belt always moves to stop the wheel from rotating.
Does this work for anyone?
-Chris
No one has an answer to my previous question? (post 395)
Hi Tony,
Look at your picture that you posted. Reverse the belt direction. That's what I'm talking about.
Hi Lostcause,
Poor Zaphod needs twice as much aspirin or alcohol as the rest of us. Can you imagine his double hangover?
-Chris
Look at your picture that you posted. Reverse the belt direction. That's what I'm talking about.
Hi Lostcause,
Poor Zaphod needs twice as much aspirin or alcohol as the rest of us. Can you imagine his double hangover?
-Chris
as i said , in reality the plane wont take off , because the belt needs to match the wheel speed , so it will turn very fast till the friction between the wheels /bearings will be so high so the plane wont move forwward- no take offmaxro said:
in theory the belt spinning at infinit speed backwards
in theory there is no such thing as infinity + take off speed
infinity is infinity , the speed will increase constantly , also the wheel speed , but , in theory again , where theres no friction between wheels /bearings -there is no forse thats stopping the plane from moving forward , as simple as that.
couple more theoretical examples :
u got a conveyor moving backwards at infinate speed ...
u put a normal plane on that belt with the engine off...
what will happen ?
nothing ! the plane remains in place - theres no friction 🙂
push the plane with your hand slightly...
whats happening now?
the plane moving forward at constant speed ...
simple rules of phisics 😉
We're reaching 50 pages and still the 3 most active posters for the "plane take off camp" cannot even reach a consensus of whether "speed" means angular velocity (in units of Rad/s) or surface speed (m/s), as well as which direction they're in?
Oh my. Please tell me debates on physical problems wont be like this when I reach grad school 🙁
Oh my. Please tell me debates on physical problems wont be like this when I reach grad school 🙁
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