Skill's weekend teaser

[MrGecko]

Actually, I'll change it now because its special Relativity, so we can call it a draw.

 

[Skill Leverage]

Actually, I'll change it now because its special Relativity, so we can call it a draw.

Is that the same as General relativity, but with prawns in?

 

[MrGecko]

Yes, but the prawns can only move in the reference frame of the dish, not it the reference frame that your gob is in.

 

[Skill Leverage]

Yes, but the prawns can only move in the reference frame of the dish, not it the reference frame that your gob is in.

How fast are these prawns spinning?

 

[MrGecko]

they have spin 1/2

 

[Skill Leverage]

oh, so they don't take off then

 

[MrGecko]

FWIW, spin 1/2 means that if you are looking the prawn in the eyes, you would have to turn it around TWICE before you see their eyes again.

Cool, eh?

 

[Skill Leverage]

That sounds like something from The Rapist's Manifesto.

 

[gooseman]

can't be bothered to read the whole of this but to me (a bloke with a degree in engineering) it seems the only relavent point is the speed of the air passing over the aerofoil (wing) that would make it fly. so given that it is being towed witht he wheels spinning but the relative motion to the floor/air is zero nothing happens .

non?

 

[Mr. Charts]

can't be bothered to read the whole of this but to me (a bloke with a degree in engineering) it seems the only relavent point is the speed of the air passing over the aerofoil (wing) that would make it fly. so given that it is being towed witht he wheels spinning but the relative motion to the floor/air is zero nothing happens .

non?

Wow! Provocative or what !

 

[Skill Leverage]

heh should be easier to explain to gooseman as an engineer:

The wheels merely spin on their axis due to the movement of the belt goose; assuming zero friction between the wheels and their axels, the net force on the plane is zero. Unlike a car, a plane does not impart its thrust through contact with the ground, it does it through the air; therefore, the belt makes no difference to the plane's takeoff.

EDIT: In case you haven't read this already; most people intuitively believe that the movement of the belt counteracts the forward motion of the plane. Think about net forces on the plane regardless of belt speed, as I've said above. Also think about a plane taking off from a sheet of ice.

 

[Skill Leverage]

Wow! Provocative or what !

not really; most people, scientists or not, get it wrong at first, it's merely intution. It's how they deal with the explanation that separates the men from the boys

 

[gooseman]

hey-i said towing, not thrust. that's a completely different matter.

solve the forces for newton's second law and voila. job done.

 

[MrGecko]

hey-i said towing, not thrust. that's a completely different matter.

Actually, I'm not sure it is...

 

[Skill Leverage]

we were talking about towing from a plane, so it wouldn't matter, but yeah if you're saying that if it was being towed by say a car that's on the belt, then yeah, it wouldn't take off.

 

[gooseman]

solve the forces then.....if the towing vehicle and the plane's wheels move at the exact same speed as the belt then nothing is going anywhere.

 

[Skill Leverage]

Yeah that's what I'm saying mate; we were saying that the towing vehicle was a plane, not a car. Besides, in the original question, the plane isn't being towed at all, it's taking off under its own steam

 

[gooseman]

right so the argument is rubbish and i'm right. that's what's important. phew.

 

[MrGecko]

right so the argument is rubbish and i'm right. that's what's important. phew.

errr.....?? Does the plane take off or not?

 

[Skill Leverage]

Incidentally if the towing vehicle was a car, the plane would still take off providing that the car wasn't on the belt. And providing it was a pretty powerful car...