Physics Puzzle

[blondini]

As the conveyor speeds up to match the wheel speed as stated, the wheels go even faster. This is a runaway runway! If you try to do this the wheels will eventually disintegrate but, unless a piece of wheel smashes into an engine, the plane will take off anyway.

Expanding this just a little further. Assuming the conveyor will be capable of matching any wheel speed, then even a slight forward movement of the aircraft would feed back via the conveyor and accelerate the wheel speed as the conveyor attempts to match it. If a balance were not reached where the conveyor speed equalled the wheel speed, i.e the aircraft stops moving forward, then the conveyor would continue to rapidly accelerate the wheel speed and exceed the point where tyre and wheel would be destroyed. How is the aircraft going to be able to roll forward if the wheels are destroyed?

 

[doitall]

I don't know what you are trying to prove diyitall apart from making yourself look like a buffoon.

Not trying to prove anything other than the plane will not take off.

Forget Newtons law, balskis law, and red herrins, forget about thrust, propulsion and even speed and traveling up the middle lane of the M1.

Softus wrote, the wheels will be moving at the same speed as the conveyor in the opposite direction, it therefor stands to reason they cancel each other out and the plane doesn't move.

 

[doitall]

As the conveyor speeds up to match the wheel speed as stated, the wheels go even faster. This is a runaway runway! If you try to do this the wheels will eventually disintegrate but, unless a piece of wheel smashes into an engine, the plane will take off anyway.

Expanding this just a little further. Assuming the conveyor will be capable of matching any wheel speed, then even a slight forward movement of the aircraft would feed back via the conveyor and accelerate the wheel speed as the conveyor attempts to match it. If a balance were not reached where the conveyor speed equalled the wheel speed, i.e the aircraft stops moving forward, then the conveyor would continue to rapidly accelerate the wheel speed and exceed the point where tyre and wheel would be destroyed. How is the aircraft going to be able to roll forward if the wheels are destroyed?

Whether the wheels are destroyed or the engine blows up is irrelevant, the question is if the two are equal will the plane take off.

The answer is No it will not.

 

[joe-90]

I can't believe this is still going on. The wheels are a red herring. The contract is between the engine (jet or propeller) and the air. The jet thrusts against the air (Newtons laws etc). What the wheels do is immaterial.

How do you work that out joe 90.

The plane is on the ground and needs a land speed to reach take off speed, that means the wheels have to turn, the problem is the ground is going the same speed in the opposite direction.

As space cat pointed out the faster the wheel speed the faster the ground travels

All it means is that at take off, instead of the wheels rotating at 180 mph - they are rotating at 360 mph - so what? The wheels aren't part of the equation as they have no thrust.

 

[blondini]

All it means is that at take off, instead of the wheels rotating at 180 mph - they are rotating at 360 mph....

360mph is 2x 180mph but why 2x Joe?

 

[doitall]

All it means is that at take off, instead of the wheels rotating at 180 mph - they are rotating at 360 mph - so what? The wheels aren't part of the equation as they have no thrust.

Without the wheels the plane cannot go forward so how can it reach air speed.

You're thinking too hard again joe90.

The wheels, them round things that allows the plane to roll is turning at exactly the same speed as the conveyor.

The conveyor is an opposite force, canceling out the spin of the wheel, that means there's no travel in any direction.[/quote]

 

[joe-90]

Because the conveyor is moving in the opposite direction. The plane is travelling at 180 mph wind speed over its wings giving it lift-off velocity. At that point the conveyor is travelling in the opposite direction at 180 mph - thus at lift off - the wheels spin at 360 mph.

 

[Balenza]

Diyitall wrote

Not trying to prove anything other than the plane will not take off.

Mythbusters have proved that the plane will take off. ( was that you flying the plane by any chance ?)
And your lame excuse to their experiment is that the conveyor they used did not act as a true conveyor.
You will have to do better.

 

[sooey]

Jesus doitall you're a stubborn old mule, answer the question I asked much earlier. If you were stood at the side of a conveyor belt with a toy plane with freely rotating wheels, and if the conveyor could magically match the speed of rotation of the planes wheels. Do you think that you would be able to hold the plane against the conveyor and move it in an opposite direction to that of the conveyor?

 

[joe-90]

Let's use an analogy:

You know those travelator things that they have at airports? Those moving walkways? OK, you are wearing roller skates and standing on one.

Both the floor and the handrail are moving at 10mph in a forward direction so your roller skate wheels aren't moving. Now something goes wrong with the handrail and it stops (though the floor keeps moving). So now you are stationary (hanging on to the handrail) and the conveyor (floor) is moving at 10 mph. Your wheels are now moving at 10 mph. Someone now switches the handrail back on but gets it running in the wrong direction. You are now hanging onto the handrail and travelling backwards at 10 mph. The conveyor (floor) is travelling forward at 10 mph. Your wheels are now travelling at 20 mph.

Now substitute the floor for the conveyor and the thrust from the engines for the handrail. You will now reach take off speed with your wheels turning at twice the speed. Gedditt yet? (he won't).

 

[xerxes]

Doitall: An easier way to conduct the experiment would be to use a supermarket trolley next time you go shopping.

Just lift the trolley onto the belt at the checkout and see if you can hold it against the movement of the belt.

Don't worry about the queues building up behind you.

But don't expect the trolley to take off ...

 

[doitall]

Diyitall wrote

Not trying to prove anything other than the plane will not take off.

Mythbusters have proved that the plane will take off. ( was that you flying the plane by any chance ?)
And your lame excuse to their experiment is that the conveyor they used did not act as a true conveyor.
You will have to do better.

Call it a conveyor if you like, the wheels were traveling faster then the conveyor.

And in any case the weight of the plane was on the ground and not the conveyor which would add drag/friction to the belt,

 

[doitall]

Jesus doitall you're a stubborn old mule, answer the question I asked much earlier. If you were stood at the side of a conveyor belt with a toy plane with freely rotating wheels, and if the conveyor could magically match the speed of rotation of the planes wheels. Do you think that you would be able to hold the plane against the conveyor and move it in an opposite direction to that of the conveyor?

If the speed of the wheels match the speed of the conveyor the plane will not move, if you push the plane along the belt then the wheels are going faster than the belt.

Think about it, even take a toy plane into Tesco if you like.

 

[NS215]

Diyitall wrote

Not trying to prove anything other than the plane will not take off.

Mythbusters have proved that the plane will take off. ( was that you flying the plane by any chance ?)
And your lame excuse to their experiment is that the conveyor they used did not act as a true conveyor.
You will have to do better.

Call it a conveyor if you like, the wheels were traveling faster then the conveyor.

And in any case the weight of the plane was on the ground and not the conveyor which would add drag/friction to the belt,

whats the difference between the floor or rollers nothing i would suggest!!!! the proof is in the pudding and the video PROVES BEYOND DOUBT THAT THE PLANE WILL TAKE OFF SIMPLE REALLY

 

[sooey]

doitall, as the engines thrust backwards, they will in turn be thrust forwards taking the attached plane with them. That is one of the basic laws of physics and is irrefutable. The only effect the conveyor can have is to make the wheels spin faster than they would normally have to. It cannot prevent the plane from moving forwards unless the brakes are on. So providing that the thrust of the engines is enough to overcome the frictional forces between wheels and axles the plane will reach take off speed.