Physics Puzzle

[doitall]

just to discount the moving walkway theory......

ok the guy is running and matching the speed of the walkway by tread-milling along, but imagine he has a jet pack strapped to his back and fires it up......


the jet pack reacts with the air and NOT with the ground.

geddit.

For that to work you would need to lift the plane off the ground, the only way the plane can move with a jet pack or a tow rope for that matter is for the wheels to turn, and if the surface the wheels are on moves in the opposite direction then the plane will not move forward

 

[noseall]

thrust from the engines at ground takeoff has everything to do with air.

 

[tim west]

You are obviously either not reading the above answers or not agreeing with them, so ok then how do the wheels affect the planes movement?

 

[noseall]

all the runway is doing is countering the energy from the wheels.

what do you suppose is countering all that energy from the reaction with the engines and the air?

 

[tim west]

ok too many alternative examples are drifting in and confusing the matter, lets just stick with the plane and runway as in the original post

 

[tim west]

all the runway is doing is countering the energy from the wheels.

what do you suppose is countering all that energy from the reaction with the engines and the air?

just to clarify my above post about not reading wasnt directed at your post you beat me to posting

 

[doitall]

You are obviously either not reading the above answers or not agreeing with them, so ok then how do the wheels affect the planes movement?

Is that a serious question

 

[crockett]

It won't take off, following the OP's original question. Obviously there are a lot of clever people trying to correctly answer this poser, but the plane needs airspeed over and under its wings to lift its bulk off the ground. If the conveyor can keep up with the thrust of the engines, then the plane will just make a lot of noise / heat etc. and not much else.

 

[tim west]

You are obviously either not reading the above answers or not agreeing with them, so ok then how do the wheels affect the planes movement?

Is that a serious question

very serious i want you to break down how the wheels affect the planes movement

 

[tim west]

It won't take off, following the OP's original question. Obviously there are a lot of clever people trying to correctly answer this poser, but the plane needs airspeed over and under its wings to lift its bulk off the ground. If the conveyor can keep up with the thrust of the engines, then the plane will just make a lot of noise / heat etc. and not much else.

see above about how the conveyor has diddly sqwat to do with anything.

 

[noseall]

in order to stop the plane moving forwards, look not at the runway but at the air or its speed relative to the engine's thrust.

que?

 

[doitall]

all the runway is doing is countering the energy from the wheels.

what do you suppose is countering all that energy from the reaction with the engines and the air?

Good example noseall.

The engine is supplying the thrust that pushes the plane forward, no problem so far as we assume the wheels have to turn.

Lets say the wheel are now doing a 100mph, but the runway is also doing a 100mph in the opposite direction, the propulsion is holding the plane stationary, e.g. to stop it shooting backwards at a 100 mph

 

[tim west]

Lets say the wheel are now doing a 100mph, but the runway is also doing a 100mph in the opposite direction, the propulsion is holding the plane stationary, e.g. to stop it shooting backwards at a 100 mph

Thats where you are wrong, the plane wouldnt move backwards if you turned off the thrust the wheels are freespinning. they apply no friction to the axle to push it backwards. the plane is like its sitting on an iceflow therefore applying thrust would have moved it forwards not holding it static as you imply.

 

[doitall]

Lets say the wheel are now doing a 100mph, but the runway is also doing a 100mph in the opposite direction, the propulsion is holding the plane stationary, e.g. to stop it shooting backwards at a 100 mph

Thats where you are wrong, the plane wouldnt move backwards if you turned off the thrust the wheels are freespinning. they apply no friction to the axle to push it backwards. the plane is like its sitting on an iceflow therefore applying thrust would have moved it forwards not holding it static as you imply.

Don't be silly, the wheels are sat on the road, therefor if the road is doing 100mph the plane and anything will also do 100mph, by applying thrust you can stop the backward travel, but the guy stood in the middle of the runway would have to hang on like grim death

 

[noseall]

the mechanics of the equation, albeit theoretical and certainly not practical, do not, in any shape or form take into account the engines' reaction to the AIR or its thrust upon it.

can you runway and wheel people not see that this force has NOT been countered?

where do you suppose this energy goes?