Physics Problem

Here's a problem that's been hotly debated on the net....

揑magine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?

I say yes it can take off, what do you guys think?

BeanDiesel

so the plane is static relative to earth right, because the velocity of the belt is the opposite of the tangential velocity of the wheels? so it won't take off. it doesn't matter how fast the speed of the wheel is, it's about how fast the speed of the wind on the wings. if it can have enough lift, it will take off. looking at the problem, it doesn't seem like it would have enough lift, if any.

bobok

kapalterbang gerak ke depan bukan sebab tayar dia tapi sebab thrust enjin dia. conveyor belt tu akan cancel rotation roda, mcm roda tu locked, tapi not really locked sbb roda tu still rotate. think about the plane taking off on ice, with all the wheels locked. the plane would still accelerate, even its wheels are not moving.

Originally posted by BeanDiesel at 13-12-2006 05:36 AM
so the plane is static relative to earth right, because the velocity of the belt is the opposite of the tangential velocity of the wheels? so it won't take off. it doesn't matter how fast the speed ...

BeanDiesel

Originally posted by sayap at 12/14/06 05:19 AM
kapalterbang gerak ke depan bukan sebab tayar dia tapi sebab thrust enjin dia. conveyor belt tu akan cancel rotation roda, mcm roda tu locked, tapi not really locked sbb roda tu still rotate. think about the plane taking off on ice, with all the wheels locked. the plane would still accelerate, even its wheels are not moving.

yes, lupa plak pasal thrust. but because belt tu match tayar nye speed, which is also the speed of the plane assuming there's no slippage, the plane is not moving relative to earth is it? so it won't take off right?
cam tire locked and plane on ice, the plane can still accelerate relative to earth, in that case it may take off.

sudugarpu

no lift.. plane will never float
even if use a catapult to launch too wil be totally waste of effort since no air-cut to keep theplane floating

windmill

depends on speed and power jugak...
kalau power cukup takder masalah untuk take off......

ussopp

I cant think!!!

kena buat experiment ni.

tatau la conveyor belt tu boleh cover speed kapalterbang ke tak sebab kalau die gune propeller atau pun jet, tentu tak de kaitan ngan tayar....camner belt tu nak cover speed die!!!

sudugarpu

tak pun pegi je kat gym...
lari atas thredmill..laju maksimum
agak2 badan makin ringan tak?
berat badan atas conveyor.. ada graviti
adakah dgn sebab belari ( thrust ) ke arah depan boleh membuat tujahan yg menyebabkan graviti hilang ( float )

ok here's my reason why I think it should take off. as sayap said, unlike a car which power acts on the wheels, a plane engine acts on the air. The wheels are basically free and have minimal friction. A good way to think about this is to imagine that you were wearing roller skates and on a treadmill, if you were to hold on to a rope attached to a fixed point u would not move but the wheels on the skates would. and if you were to exert a force on the rope (i.e. pull it) you would move forwards even through the treadmill is trying to pull you backwards. You would imagine that the amount of effort needed to pull yourself forward would'nt be that great, as long as your wheels are well oiled.

BeanDiesel

Originally posted by exdua at 12/16/06 04:18 AM
ok here's my reason why I think it should take off. as sayap said, unlike a car which power acts on the wheels, a plane engine acts on the air. The wheels are basically free and have minimal fricti ...

that's actually a good analogy.

yes, i think the plane may have enough lift. the net horizontal force can be more than zero, so the plane can accelerate.

seladanganas

sebenarnya tak boleh terbang sebab k'tebang memerlukan true airspeed yg secukupnya utk generate enough lift off the ground regardless of ground speed. kalau conveyer tu bergerak selaju kapalterbang itu sendiri maka tak ada fwd speed maka airspeednya  kosong jadi takadalah lift yg boleh digenerate oleh wing. bagi k'tebang penumpang mcm boeing 737,747, airbus 320,330,340 biasanya memerlukan lebihkurang 130 knot utk generate enough lift utk takeoff. ini dipanggil decision speed yg mana lepas dari ni pilot memang kena t/off, tak boleh buat rejected t/off( tarik engine throttle, tekan brake maksimum dan deploy thrust reverser). bila k'tebang dah mula terangkat maknanya dah ada lift baru dia rotate, tarik control column, elevator akan memusingkan k'tebang agar hidungnya menjongket dan terus climb.

me_ai

okey...nak cuba pandangan aku lak...

Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway:
katakan pada mula keadaan, kpl terbang dgn conveyor masing tidak bergerak,
laju, pecutan semua = 0.
jarak tidak berubah.

seterusnya
thrust force dari enjin akan gerakkan kpl terbang, mnyebabkan tayar kapal terbang mula berputar.
The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction
berdasarkan ayat atas, jika ada pertambahan halaju pada tayar kapal terbang, halaju conveyor juga akan bertambah.
pertambahan halaju sama dgn halaju putaran tayar kpl terbang
kiraan halaju sudut semua...tambah tolak akan dapat....pecutan bertambah...
tp adakah jarak berubah...jarak tdk berubah.

jadi wpun thrust force yg dihasilkan enjin sudah cukup atau lebih dari yg diperlukan utk menerbangkan kpl terbang, disebabkan permukaan conveyor belt yg turut berputar, melawan arah pergereakkan roda kpl terbang, sudah tentu, kesan aerodynamic pada sayap kpl terbang tidak berlaku.

kesan aerodinamic bg kpl terbang, daya angkat (lift) ialah kesan dari pergerakkan udara di bahagian aerofoil sayap kpl terbang.
2 cara utk mdptkan pergerakkan udara, angin(mustahil utk mengangkat kpl terbang)
dan objek memecut sekata(pergerakkan kpl terbang)
dlm kes ini kpl terbang tak bergerak.

kesan yg sama bila kita hantar kereta kita ke pusat servis. utk periksa odometer(meter halaju)
ada satu platform dgn roller. tayar kereta akan diletakkan dia atas roller
bila tayar kereta bergerak. roller juga akan bergerak.
kereta tak ebrubah kedudukan.

me_ai

A good way to think about this is to imagine that you were wearing roller skates and on a treadmill, if you were to hold on to a rope attached to a fixed point u would not move but the wheels on the skates would

OK..roller skate on threadmill...opposite rotationbetween roller skates and threadmill...and holding on fixed rope.
condition semua ok...threadmill bergerak pd laju yg sama dgn roller, disebbakan kedudukan statik pemakai roller skates.

tetapi jika pemakai roller skate menarik tali, halaju roller akan bertambah...

so dah tak sama dgn condition post pertama.
keadaa roda kpl terbang dan conveyor sama laju

meitantei

Utk jawab soalan ni, kenalah buat beberapa assumptions

1. Assume eksperimen ni di buat di runway dgn normal conditions. Ie. ader udara, typical fine weather.

2. Assume tayar kapal terbang sentiasa melekat pada conveyor belt di mana kalau roda kapal terbang berpusing, conveyor belt bergerak sama.

Kalau kita buat these assumptions, maka kapal terbang takkan terbang. Sebab kapal terbang tu tak bergerak (displacement/sesaran = 0). Sebab tuk kapal terbang terbang, perlu ader udara yg bergerak sekeliling sayap (Bernoulli Principle)...

rdzaccess

Kapalterbang??
Nak tanya sikit.
Enjin dia running ke tidak?Berapa thrust enjin dia?Berapa berat kapal terbang tersebut?Berapa panjang sayap dia(wings span)?'Free air movement/wind velocity'.

Kalau kapalterbang tersebut di dalam keadaan pegun, kapalterbang itu akan berundur kebelakang.Ini disebabkan oleh'torque' dari conveyor adalah lebih kuat dari roda kapalterbang tersebut walau pun kelajuan tayar bersamaan dengan kelajuan conveyor.Tetapi dengan pengendalian oleh juruterbang kapalterbang tersebut boleh terangkat kerana conveyor tersebut adalah sepanjang dan selebar landasan berlawanan dengan kelebaran kapalterbang. Kita tidak boleh menolak fakta bahawa angin yang dihasilkan oleh conveyor belt menujah ke arah sayap kapalterbang. Jadi kapalterbang akan terangkat ke atas (faktor rekaan sayap) tanpa  
menggunakan enjin ia adalah seperti glider ( perhati sifat pepatung dalam penerbangan pegun).

meitantei

Originally posted by rdzaccess at 1-6-2007 12:18 AM


Kapalterbang??
Nak tanya sikit.
Enjin dia running ke tidak?Berapa thrust enjin dia?Berapa berat kapal terbang tersebut?Berapa panjang sayap dia(wings span)?'Free air movement/wind veloci ...

I disagree. Kalau conveyor belt tu bergerak dgn speed sama dengan tayar kapal terbang, maka tak ada torque akan dihasilkan.

Torque = Force x perpendicular distance between axis of rotation and the line of action of the force

Masalahnya, laju tayar = laju conveyor belt. Jadi tak ada acceleration. Takde acceleration takde Force. Takde force, maka takder torque.

meitantei

I've got a new insight of this problem.

Putting a plane on a conveyor belt that will move in the opposite direction at a speed equal to the speed of the tyres is like suspending the plane in midair and letting the tyres of the plane turn.

When we suspend a plane in midair, the speed of the air surrounding the tyres will move at the same speed (almost) as the tyres. Hence, apropos to the question, the plane would be stationary relative to the ground.

pixy

yang nak menerbangkan kapal terbang tu .. aliran angin .. bukan tayar
kalau tayar bergolek sampai pecah pun atas conveyor tu .. tapi relatively kapal terbang tak bergerak pun .. camne nak terbang..

masrini

aduiiii pening.....................

matamata

Kapal terbang take off berdasarkan pada Prinsip Bernoulli yg di aplikasikan pada sayap kapal terbang tu sendiri. Kalau Prinsip Bernoulli tu tak dipatuhi maka kapal terbang takkan terbang. Perlukan kelajuan tertentu (paling senang kapal terbang akan terbang lawan arah angin), perlukan ketumpatan angin tertentu untuk lawan graviti. itulah secara singkasnya. nak explain panjang2 jari akupun blh patah menaip