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re: Can this 747 take off?
Posted on 4/11/24 at 9:39 pm to meansonny
Posted on 4/11/24 at 9:39 pm to meansonny
quote:
The friction of the treadmill isn't going to have any effect on 240,000 horsepower thrusting forward.
The friction of the treadmill will have an impact on wheels approaching the speed of infinite though. And then on rims when they burn up, and so on and so on. Until that plane is sitting on its belly or blows up.
Tell me a jet can take off with the wheels completely locked up, go on.
do it. 
1
Posted on 4/11/24 at 9:39 pm to PhysicsGuy
Yes I get it that it’s impossible but the riddle implies that the speeds match, any natural scenario would have the thrust force dominate the frictional drag.
Posted on 4/11/24 at 9:44 pm to Power-Dome
quote:
How is wheel speed going to be different than any other part of the plane
The wheels are free. Like a hot wheels car.
The wheels can spin 1000 revolutions a minute and the plan doesn't move (i.e. treadmill).
And with the thrust of a jet plane, you could put a brake on the wheels so they don't spin and the thrust would still be sufficient to push the plane into liftoff.
Posted on 4/11/24 at 9:46 pm to NATidefan
quote:
Tell me a jet can take off with the wheels completely locked up, go on. do it.
You underestimate 4 jet engines at 240,000 horsepower.
They could be the big bad wolf and blow a small home down. Rubber tires aren't going to have much of a chance holding it still.
This post was edited on 4/11/24 at 9:47 pm
Posted on 4/11/24 at 9:50 pm to Power-Dome
It doesn’t imply that, you interpreted it that way. The question is from world of engineering and it says the belt is designed to match the speed.
Engineering answer is it’s not possible to design it mathematically. What happens is the backwards speed of the belt is offset by the forward speed of the wheels, as designed…As soon as the engines add an independent source of forward motion the belt will perpetually be behind by that number.
You increase the belt by 1000 mph the wheels go 1000 mph faster so they cancel each other out. You’re left with only the forward thrust and the plane takes off as normal.
Engineering answer is it’s not possible to design it mathematically. What happens is the backwards speed of the belt is offset by the forward speed of the wheels, as designed…As soon as the engines add an independent source of forward motion the belt will perpetually be behind by that number.
You increase the belt by 1000 mph the wheels go 1000 mph faster so they cancel each other out. You’re left with only the forward thrust and the plane takes off as normal.
This post was edited on 4/11/24 at 9:52 pm
Posted on 4/11/24 at 9:51 pm to PhysicsGuy
Guys, it doesn’t matter if the treadmill can match the speed or not. frick it, make it to where the treadmill is going backward 2x faster backward than the plane ever could move forward.
THE PLANE STILL TAKES OFF
THE PLANE STILL TAKES OFF
This post was edited on 4/11/24 at 9:52 pm
Posted on 4/11/24 at 9:53 pm to PhysicsGuy
quote:si the wheels be moving faster than the belt
As soon as the engines add an independent source of forward motion the belt will perpetually be behind by that number.
Posted on 4/11/24 at 9:55 pm to tigerfoot
Correct, because even if designed perfectly the belt will always fail to match.
Posted on 4/11/24 at 10:00 pm to PhysicsGuy
So we ignore the parameters of the riddle
Posted on 4/11/24 at 10:00 pm to PhysicsGuy
quote:
The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction...
I looked at it again, and think if everyone agreed About this statement. We’d have agreement.
If “speed”= wheel rotation, the plane will move forward until lift is achieved regardless whether the windmill hit infinity.
If speed= objective placement between the treadmill and the landing gear, then you achieve the scenario of a perpetually stationary object.
Posted on 4/11/24 at 10:01 pm to PhysicsGuy
My interpretation in this rolling-friction-counter-force model was that the tread goes fast enough that the center axle as zero velocity. The vectors at the top and bottom of the wheel would be equal and opposite.
I posed a thought experiment earlier with a small toy plane with no engines on needing to be held in place to keep from falling off the back of a running household treadmill. Obviously there is a force transmitted tangentially to a free rolling object to send it off the back of a treadmill, no? And could there not theoretically be a tremendously fast treadmill that could produce enough of this tangential force to counteract the thrust?
I posed a thought experiment earlier with a small toy plane with no engines on needing to be held in place to keep from falling off the back of a running household treadmill. Obviously there is a force transmitted tangentially to a free rolling object to send it off the back of a treadmill, no? And could there not theoretically be a tremendously fast treadmill that could produce enough of this tangential force to counteract the thrust?
This post was edited on 4/11/24 at 10:03 pm
Posted on 4/11/24 at 10:09 pm to Power-Dome
My man the speed of the wheels is speed of the belt plus speed from thrust. If the speed from thrust is 10, you can pick any number you want for the speed of the belt because the speed of the wheels will be that number plus 10. X can never equal X+10.
Posted on 4/11/24 at 10:10 pm to lsuconnman
That’s literally what the question says, if people don’t agree with it then they are answering a different riddle.
Posted on 4/11/24 at 10:16 pm to PhysicsGuy
quote:
PhysicsGuy
User name checks out.
Posted on 4/11/24 at 10:19 pm to tigerfoot
No we don’t. Why is everyone so hung up on this. What does the riddle actually say? Have you never heard of something not doing what’s it’s designed to do? It’s designed to match the speed, math says it can’t. The question doesn’t say the wheels can never move faster.
You guys are all reading that into a question that doesn’t say that. Which is the point of the question and all questions like this. It preys on people’s brains filling in assumptions that the question writer knows will happen and are also wrong.
You guys are all reading that into a question that doesn’t say that. Which is the point of the question and all questions like this. It preys on people’s brains filling in assumptions that the question writer knows will happen and are also wrong.
Posted on 4/11/24 at 10:22 pm to Street Hawk
quote:
Prove to us it will work. Please pass along your work. Or do an Einstein thought experiment and just write the prose.
Ok...
Mythbusters actually did this already. This first video is the explanation of why people argue and where they are wrong and you get your answer at the 06:45 mark...
"Yes, the plane will always take off"
Explanation
Video of the experiment...
LINK
Pilot: "I was really surprised it just took off normally. I thought that I would just sit here like a brick."
This post was edited on 4/11/24 at 10:28 pm
Posted on 4/11/24 at 10:23 pm to im4LSU
Yep the plane will just behave normally.
Posted on 4/11/24 at 10:34 pm to PhysicsGuy
quote:
The question doesn’t say the wheels can never move faster.
It says they move exactly the same speed.
In the myth busters experiment what was the rotation of the tire? The same or faster?
Posted on 4/11/24 at 10:36 pm to tigerfoot
quote:
In the myth busters experiment what was the rotation of the tire? The same or faster?
I don’t recall them giving an exact speed but Jamie said once he got going he pretty much gunned it and that plane never even checked up.
Posted on 4/11/24 at 10:42 pm to im4LSU
They didn’t. The experiment they conducted proved that the thrust of the plane overcame the speed of the treadmill.
No one debated that point.
No one debated that point.
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