Slinky physics question
Discussion
The vast majority of us said no as the plane would not generate lift and therefore could not get it's ass off the ground.
With the slinky though, unless there is anything that will give resistance, I think it will just keep going and stay in the same spot as long as the excaltor keeps going, the minute that stops the slinky will just continue down until it meets resistance... ie the floor!
With the slinky though, unless there is anything that will give resistance, I think it will just keep going and stay in the same spot as long as the excaltor keeps going, the minute that stops the slinky will just continue down until it meets resistance... ie the floor!
The plane will eventually exceed the limits of it's tyres and crash horribly without taking off (it's airspeed and it's groundspeed would have remained c. zero, so no lift). The conveyor belt will send it's fiery corpse hurtling backwards towards the terminal, killing thousands!!!
Back to the slinky...
The slinky will continue in perpetuity, as there is an external source of energy - whatever is powering the escalator.
Back to the slinky...
The slinky will continue in perpetuity, as there is an external source of energy - whatever is powering the escalator.
speedchick said:
With the slinky though, unless there is anything that will give resistance, I think it will just keep going and stay in the same spot as long as the excaltor keeps going, the minute that stops the slinky will just continue down until it meets resistance... ie the floor!
Rather like a person will continue to fall through the air at a constant speed ( terminal velocity ) until the meet the resistance of the ground.
The question of the initial "flick" to get it going and the loss of this energy could be removed by using a tall slinky and slightly tilted escalator steps, set it up so that the slinky will fall (centre of gravity falling outside its base).
This one should continue until either the elevator stops (and it goes all the way down the elevator) or it hits the side (where it may still rebound and continue, I've seen em do it).
This one should continue until either the elevator stops (and it goes all the way down the elevator) or it hits the side (where it may still rebound and continue, I've seen em do it).
Raffles said:
The only way the plane would not take off would be if the wheels were driven, which can't be the case.
The conveyor belt it's on would make no difference, as the jet/props use the air to create thrust.
If the conveyor under plane was moving as fast as the plane, it would have no forward motion, so no lift would be created.
If we accept that the tyres can revolve fast enough and nto explode then all of the engergy from the jets, propellors whatever is being disappaited by the wheels.
Think about it, when your running along at 10mph on a treadmill in the gym there's no wind at all in your face, but run along the road and you feel a breeze on your face as the air flows around you.
axeman30 said:
The only way the plane would not take off would be if the wheels were driven, which can't be the case.
The conveyor belt it's on would make no difference, as the jet/props use the air to create thrust.
If the conveyor under plane was moving as fast as the plane, it would have no forward motion, so no lift would be created.
If we accept that the tyres can revolve fast enough and nto explode then all of the engergy from the jets, propellors whatever is being disappaited by the wheels.
Think about it, when your running along at 10mph on a treadmill in the gym there's no wind at all in your face, but run along the road and you feel a breeze on your face as the air flows around you.
game, set and match i think
axeman30 said:Indeed. The only way that lift can be generated is with airflow.
Think about it, when your running along at 10mph on a treadmill in the gym there's no wind at all in your face, but run along the road and you feel a breeze on your face as the air flows around you.
If the aircraft is stationary relative to its surroundings, which would be as a result of all its thrust being used to retain its relative position rather than being moved backwards by the conveyor belt, then although its speed relative to the belt would increase its speed relative to its surroundings would not (assuming the conveyor belt's speed and acceleration exactly matched the plane's speed and acceleration).
However, were you to introduce a wind tunnel into the equation, then the plane would indeed be able to become airborne and could appear to hover since the airflow from the wind tunnel would be generating lift. I say hover, but that assumes the forward speed of the aircraft is matched by the speed of the airflow from the wind tunnel.
Now, introduce a spherical cow into the equation, and all bets are off.
>> Edited by JonRB on Thursday 8th December 14:05
axeman30 said:
The only way the plane would not take off would be if the wheels were driven, which can't be the case.
The conveyor belt it's on would make no difference, as the jet/props use the air to create thrust.
If the conveyor under plane was moving as fast as the plane, it would have no forward motion, so no lift would be created.
If we accept that the tyres can revolve fast enough and nto explode then all of the engergy from the jets, propellors whatever is being disappaited by the wheels.
Think about it, when your running along at 10mph on a treadmill in the gym there's no wind at all in your face, but run along the road and you feel a breeze on your face as the air flows around you.
I'm with Raffles on this.
Think about it, when you run on a treadmill the drive to go forwards comes through your legs. Get on the same treadmill wearing rollerskates, hold onto something like a rope attached in front of you and where do you go? no where!
The only force required to keep you still is enough to oversome the drag in the roller skate wheel bearings.
Now, holding said rope, wearing said roller skates, get a mate to push on your back, or even pull the rope if you like - what happens? you move forwards.
So, with a plane on a conveyor, the engines would need t osupply an additional force to over come the drag in the wheels and conveyor, given enough force the plane will move forwards, eventually hitting take off speed.
jjsmudge said:
But the jets act on the air and not the runway. The wheels of the plane are not what moves it along, they are just there to keep it off the runway so the plane will take off.
Makes no difference where the thrust is generated, all of the forward thrust from the jets is still dissapated through the wheels which are in contact with the ground and made 'sticky' by friction with it.
Once the wheels are no longer in contact with the ground things are different, the planes weight is balanced by the lift of the wings and the wheels cannot dissapate engery to the ground and so the energy can push the plane forwards through the air.
But our plane in on a treadmill in effect.
axeman30 said:
Makes no difference where the thrust is generated, all of the forward thrust from the jets is still dissapated through the wheels which are in contact with the ground and made 'sticky' by friction with it.
Have we been sucked into a parallel universe where the cartoon rules of physics apply? If so presumably when you switch off the conveyor belt the plane will immediately zoom off an a million miles an hour and leave the pilot smeared against the windscreen when it runs off the end of the conveyor belt.
axeman30 said:
But the jets act on the air and not the runway. The wheels of the plane are not what moves it along, they are just there to keep it off the runway so the plane will take off.
Makes no difference where the thrust is generated, all of the forward thrust from the jets is still dissapated through the wheels which are in contact with the ground and made 'sticky' by friction with it.
Once the wheels are no longer in contact with the ground things are different, the planes weight is balanced by the lift of the wings and the wheels cannot dissapate engery to the ground and so the energy can push the plane forwards through the air.
But our plane in on a treadmill in effect.
Cobblers!
(in the nicest possible way!) If that were the case the 'plane would fall to earth the moment the wheels left the ground cos the wheels couldn't drive the 'plane forward.! No, Raffles IS right and the ground is irrelevant except as a support for the 'plane while it gains airspeed. The jets or props drive by reaction against air, NOT the runway.motco said:
Cobblers!
motco...... when you next take your car out on a rolling road and rev it up to 70mph... put your head out of the window and tell me what you feel.
..... do you think that if the said car was powered by a large fan stuck on the roof, or even a jet than it would go flying off the rolling road?
>> Edited by axeman30 on Thursday 8th December 14:43
I've googled this a bit, and am willing to take another point of view on it.
It's all in the wording of the question, and if you stick strictly to what the question states, then no the aircraft would not take off.
What the question states if that the conveyor matches the forward speed of the aeorplane, cunningly hidden by talking about wheels.
For every metre that the wheel rotation takes the plane forward, the conveyor carries the plane backwards that same distance, thus there is no forward motion of the plane, just a lot of rotatation going on at the wheels.
With no forward motion there is no air flow over the wings, and no lift. So in the exact context of the question which implies that a ground speed of zero is maintained it (the plain) goes no where.
In the real world of course this is nonsense, the engines would soon overcome any limiting friction holding the plane from going forwards, by the time enough ground speed is achieved then the wheels might be turning 1000's faster than normal, but the plane would have the forward motion.
It's all in the wording of the question, and if you stick strictly to what the question states, then no the aircraft would not take off.
What the question states if that the conveyor matches the forward speed of the aeorplane, cunningly hidden by talking about wheels.
For every metre that the wheel rotation takes the plane forward, the conveyor carries the plane backwards that same distance, thus there is no forward motion of the plane, just a lot of rotatation going on at the wheels.
With no forward motion there is no air flow over the wings, and no lift. So in the exact context of the question which implies that a ground speed of zero is maintained it (the plain) goes no where.
In the real world of course this is nonsense, the engines would soon overcome any limiting friction holding the plane from going forwards, by the time enough ground speed is achieved then the wheels might be turning 1000's faster than normal, but the plane would have the forward motion.
Hang on, at first I agreed with the "no airflow = no lift"
but now I think about it, the wheels and the conveyor belt are irrelevant. Unless the brakes are on, the plane will move forward due to the thrust created by the engines. The conveyor belts spins uselessly, rotating the wheels, uselessly
Or am I being dumb?
but now I think about it, the wheels and the conveyor belt are irrelevant. Unless the brakes are on, the plane will move forward due to the thrust created by the engines. The conveyor belts spins uselessly, rotating the wheels, uselessly
Or am I being dumb?
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