Physics Puzzle
- Thread starter Softus
- Start date
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the OP was describing something that cannot occur so you are wasting your time trying to answer.
Why can't it happen
if you hold your toy on Tesco's conveyor, the contact between the wheel and the belt will be the same speed. if you apply thrust and push the toy forwards the wheel speed will be greater.
The confusion around here all goes back to the wording of the original post. As Softus says --
It certainly does. Here's the crunch question: What, exactly, is meant by "wheel speed"?
And I'll add another one: From which reference point is it measured?
Since things are bad enough already without introducing passing astronauts, let's take the ground as our reference point. Now, about those wheels. Did Softus mean axle speed or circumferential, ie tyre, speed?
If he meant axle speed there is no problem. The plane accelerates forwards under engine power until it reaches take-off speed. Meanwhile, the conveyor accelerates backwards. This will cause the wheels to spin twice as fast as they would have done on a fixed runway but, unless they disintegrate, the plane will take off anyway.
If he meant tyre speed we have a problem. As I pointed out way back, the control system will go out of control trying to achieve the impossible. This, I believe is, the crux of doitall's argument:
1) The control system works - perfectly.
2) If the plane moves, the control system hasn't worked.
3) The plane can't move.
As an argument in semantics it's flawless - unless the first statement is false.
Actually, there is a way out of this mess. If we shift our reference point to the plane, the tyre speed will be observed to be the same as that of the conveyor below. Problem solved!
But isn't that cheating? No, because, regardless of how we define wheel speed, the control system can only function perfectly if the conveyor and the wheels are massless. Can you see where this is leading? When the conveyor reaches light speed it will be travelling at the same speed as the tyres and it doesn't matter whether you observe this from the ground or from the plane or from outer space. The control system works perfectly and the plane takes off.
It certainly does. Here's the crunch question: What, exactly, is meant by "wheel speed"?
And I'll add another one: From which reference point is it measured?
Since things are bad enough already without introducing passing astronauts, let's take the ground as our reference point.
Now, about those wheels. Did Softus mean axle speed or circumferential, ie tyre, speed? If he meant axle speed there is no problem. The plane accelerates forwards under engine power until it reaches take-off speed. Meanwhile, the conveyor accelerates backwards. This will cause the wheels to spin twice as fast as they would have done on a fixed runway but, unless they disintegrate, the plane will take off anyway.
If he meant tyre speed we have a problem. As I pointed out way back, the control system will go out of control trying to achieve the impossible. This, I believe is, the crux of doitall's argument:
1) The control system works - perfectly.
2) If the plane moves, the control system hasn't worked.
3) The plane can't move.
As an argument in semantics it's flawless - unless the first statement is false.
Actually, there is a way out of this mess. If we shift our reference point to the plane, the tyre speed will be observed to be the same as that of the conveyor below. Problem solved!
But isn't that cheating?
No, because, regardless of how we define wheel speed, the control system can only function perfectly if the conveyor and the wheels are massless. Can you see where this is leading? When the conveyor reaches light speed it will be travelling at the same speed as the tyres and it doesn't matter whether you observe this from the ground or from the plane or from outer space. The control system works perfectly and the plane takes off. if the wheels and conveyor reach lightspeed hypothetically then wouldnt a time dilation effect take place and the planes wheels and the conveyor would dissappear into an alternative dimension, the ploane is free as always to take off.The confusion around here all goes back to the wording of the original post. As Softus says --
It certainly does. Here's the crunch question: What, exactly, is meant by "wheel speed"?
And I'll add another one: From which reference point is it measured?
Since things are bad enough already without introducing passing astronauts, let's take the ground as our reference point.
If he meant axle speed there is no problem. The plane accelerates forwards under engine power until it reaches take-off speed. Meanwhile, the conveyor accelerates backwards. This will cause the wheels to spin twice as fast as they would have done on a fixed runway but, unless they disintegrate, the plane will take off anyway.
If he meant tyre speed we have a problem. As I pointed out way back, the control system will go out of control trying to achieve the impossible. This, I believe is, the crux of doitall's argument:
1) The control system works - perfectly.
2) If the plane moves, the control system hasn't worked.
3) The plane can't move.
As an argument in semantics it's flawless - unless the first statement is false.
Actually, there is a way out of this mess. If we shift our reference point to the plane, the tyre speed will be observed to be the same as that of the conveyor below. Problem solved!
But isn't that cheating?
Why can't it happen
Define speed in relation to the original question ?.
they coneyror, moving at equal and oppisite speed to the aircraft, can only happen in two conditions:
3) The plane is stationary
2) The plane and conveyor are both moving at infinite speed
Hence the question is defective and you cannot solve it.
If you don't believe me, try to work out the conveyor speed if the aircraft is moving at 1mph
Landspeed is measure at the point of contact between the tyre and the surface, as I said somewhere a big wheel will turn slower than a smaller one yet still be doing the same speed.
Therefor if the speed of the wheel and the conveyor is the same the wheel cannot move forward, at any speed.
There's nothing scientific about it, it's fact.
Hold the toy on the belt and the contact between the two surfaces will be the same mph
a big wheel will turn slower than a smaller one yet still be doing the same speed.Therefor if the speed of the wheel and the conveyor is the same the wheel cannot move forward, at any speed.
There's nothing scientific about it, it's fact.
Hold the toy on the belt and the contact between the two surfaces will be the same mph
Landspeed is measure at the point of contact between the tyre and the surface, as I said somewhere
Therefor if the speed of the wheel and the conveyor is the same the wheel cannot move forward, at any speed.
There's nothing scientific about it, it's fact.
Hold the toy on the belt and the contact between the two surfaces will be the same mph
Whats the matter ?. Question too difficult ?.
The aircraft will move. Its already travelling at 1mph in relation to a fixed point on the ground.
Start up the conveyor and the wheel rpm increases.
Now that question again.
Define speed in relation to the original question ?.
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