A harmless little riddle

That didn't come out right. The runner would need to create propulsive force to overcome the belt, whcih is moving the runner backward at every foot strike. With a plane, there is no foot strike, there is no movement backward...once the wheels spin, there will be enough thrust to counteract minimal friction.

You are right, if you go forward before the treadmill. But since we are dealing with a hypothetical problem, maybe even without gravity or friction, the treadmill increases its' acceleration with you. But since without gravity or friction, the only you would be able to make any net forward movement, you would not be able to have any change in pressure over your wings that would allow you to take off. Your idea is good, but I think that there are too many variables to let it really take effect.

Here's the way to test this riddle. Set up a treadmill in a gymnasium. Start running on the treadmill at 6 mph. We can all agree that the treadmill is going in the opposite direction at 6 mph. Now, throw a kite up into the air. Does it fly? That should settle it.

Ex- Thrower wrote:

Here's the way to test this riddle. Set up a treadmill in a gymnasium. Start running on the treadmill at 6 mph. We can all agree that the treadmill is going in the opposite direction at 6 mph. Now, throw a kite up into the air. Does it fly? That should settle it.

If you put a key on the kite it will unlock untold wonders to your eyes ..and your eyes alone.

The plane will take off because it WILL move forward.

In short, because the wheels turn freely, the speed of the treadmill HAS NO EFFECT on the motion of the plane relative to the ground (not relative to the treadmill). The jets will move the plane forward relative to the ground no matter what speed the treadmill is at.

To see this, consider the following scenario. Imagine that you have a plane sitting on the treadmill and that you never turn on the engines. Now turn the treadmill on SUDDENLY to 100 mph. The wheels on the plane ROTATE FREELY, so they begin begin to turn. In this case, the plane will remain stationary even though the treadmill is running at a very high speed (the plane will not move backward at the same speed of the treadmill).

genius boy wrote:

To see this, consider the following scenario. Imagine that you have a plane sitting on the treadmill and that you never turn on the engines. Now turn the treadmill on SUDDENLY to 100 mph. The wheels on the plane ROTATE FREELY, so they begin begin to turn. In this case, the plane will remain stationary even though the treadmill is running at a very high speed (the plane will not move backward at the same speed of the treadmill).

Actually, the plane will fly off the back of the treadmill. Have you ever seen the jackass episode when they try to skateboard on the treadmill? They fly off the back and hurt themselves.

Also, the weight of the plane will keep the wheels incontact with the treadmill. Winds of 150 mph would have to pass over/under the wings to remove the wheels from the treadmill, but inorder of those kinds of winds to pass over/under the wings it would have to move fowards, but as long as the wheels are in contact with the treadmill it can't move foward. Make sense?

If the plane was hovering over the ground, then we turned on the engines it would move foward. But as long as gravity is present, the wheels touch the ground, the plane can't move foward, the plane can't take off.

No the plane will not fly off the back of the treadmill. Quoting jackass will do nothing to further your point in a scientific discussion.

Take this scenario. A plane is landing on a runway. This is essentially the same as the above posters scenario where a plane is on a treadmill that is instantly acccerlerated to 150 mph, if you simply consider a different reference frame (ie. relative to each other the plane and the ground are moving past each other at 150 mph, and the plane and the treadmill are also moving past one another at 150 mph). Now, if what you say if true, that the plane would shoot off the end of the treadmill (ie. the relative velocities would fall to zero also instantaneously), then when a plane lands on a runway, it would instantly stop. As we know this is not true.

What anyone who says the plane would not takeoff fails to realize is that the wheels on a plane DO NOT is any way shape or form affect the forward motion (or lack thereof) of the plane. If you draw a physics force diagram of the plane (simply considering horizontal motion), there would be three main forces acting upon it going down the treadmill. Force one, pointing, we will say left, is the engine thrust. Force two, which would point right, is the air resistance. Force three, which would point right, is the frictional force generated by the contact of the wheels on the ground. Now, the frictional force must be very very small compared to the thrust force. Why? The plane can be pulled by docking trucks into gates, so those trucks must be able to overcome the frictional force of the wheels, but those same trucks cannot even come close to accelerating the plane enough to produce the speed required for takeoff, hence, the thrust force is many times greater than the frictional force from the wheels. Now, with no treadmill, the wheels will have a certain frictional force. Obviously, plane overcomes this force and the air resistance to takeoff. Now we put the plane on our giant treadmill. The frictional force will be doubled, since the ground is now moving backwards instead of stationary. However, as stated before, the frictional force is many times smaller than the thrust force, so when doubled it will still be much smaller than the thrust force. Now, the thrust force is the same as without the treadmill, the air resistance is the same, and the tiny frictional force has been doubled. What is the net result when the forces are combined? The net force will be decreased slightly, but there is still a large net force in the direction of the thrust force, hence the plane will accelerate in that direction and takeoff. The only difference is that it might take one or two more meters of runway before takeoff to compensate for the added friction.

What this aerospace guy doesn't understand is that if a runner is going at 10mph on a treadmill that is going backwards at 10mph that does not relate to the riddle. That's because the runners speed to the ground would be 0mph and that is the speed that would be matched by the treadmill, not the runners speed relative to the treadmill. It is the ground speed that is matched by the treadmill.

So it then becomes obvious that whatever speed the runner is going relative to the treadmill, the treadmill would be going half that speed in the opposite direction. If the runner stood on a treadmill that wasn't moving, all speeds would be 0. If he started to run at a 10mph pace the treadmill would go 5mph in the opposite direction. In that way the runners ground speed would be 5mph (10-5=5) and the treadmill speed would be 5mph. The runner, or plane, or whatever, would be able to move forward while the condition of the riddle is met.

this very SIMPLE explanation bypasses all the talk about friction and wheels.

im not going to answer this, im just going to throw something out there to f*** with ur heads a little. pick a different reference frame. say ur a point on the treadmill way ahead of the plane. according to you, the treadmill (yourself) never moves, but the airplane and the air surrounding u seems to move at great speeds....

heres another one, lets say a plane is in flight, flies low enough to touch its wheels to the ground, lands on this huge conveyer belt, the conveyer belt can be still, moving at 70 mph, or 10000 mph, this just affects how fast the wheels move... the plane will still be flying through the air, the conveyer belt cant stop a plane by acting on its wheels, in the same fashion the conveyer belt cant keep a plane from taking off either.

u cant relate this to a runner or a car on a treadmill. think back to when ur were a little kid and played with hot wheels. u would use ur hand to move them around on the ground. imagine u went to ur parents treadmill and turned it on. would the treadmill keep u from moving it forward? no, the wheels would just spin faster. the same principle is applied to the plane. the thrust from the air is totally separate from the wheels and the treadmill. its not possible for the treadmill to keep it stationary. u lay down ur hot wheel on a stationary treadmill, they both dont move. u turn on the treadmill, and the car moves backwards and falls off the treadmill. turn the treadmill off, and put the car back on, only this time u keep ur hand behind it. u turn the treadmill on and the car stays put, and the wheels spin and the treadmill spins. slowing u apply more force to the back of the car, and it moves forward. now, u could say, wait, the treadmill is still going the same speed, in the riddle the treadmill always matches the speed of the plane... ok, so are u trying to tell me that the treadmill is somehow going to keep ur little arm from moving that car forward? of course not. see the treadmill wouldnt "know" to accelerate to begin with, it only spins the wheels. the wheels dont "know" either. they are irrelevant. its ur arm that moves the hot wheel. the treadmill and wheels just spin along. the plane is the same way, only the propellers spin, creating a thrust, this thrust is synonomous with the force applied by the kids arm. therefore, the riddle is like a loaded question. it assumes the treadmill can somehow keep the plane stationary, when in fact, it cannot.

<-----Actual aerospace guy wrote:

Sea planes and ski planes take off by reaching a fast enough speed so that the air moving under the wings is moving by fast enough to provide lift.

If you were an "actual aerospace guy" you wouldn't have posted this.

Most of the lift is generated on the upper surface of an aerofoil.

its a riddle the riddle puts in something that "seems" relevant but in actuality is not at all. The tredmill is there for one and only purpose...to throw you off. When you jump in the air you do not go backwards 500 ft, even though the world is spinning at approximately 1000 mph. If you can understand that then you can understand the treadmill and the wheels have nothing to do with the force applied by the engines. Just about everyone that has read this post keeps talking about the treadmill when it has nothing to do with the question. It is just something to throw people off. you could reverse the tredmill and have it going 1000 mph in reverse and that would not make the plane take off because the wheels are independent of the engines unlike a car which has a drive train connected to the wheels. The plane would take off no matter how fast the wheels are spinning in the opposite the direction. the wheels could spin 1000, or 1,000,000 mph in the opposite direction and with thrust applied to the enginges the plane would still take off in the same amount of time a plane on a normal stationary runway would. The same amount of time. YES I am right and anyone else agrees with yes if "WOULD" take off. GO BOs! Tron Bo, Espo Bo, S Bo, A BO, Willie Bo...where the brains are at. TN is where the smarts are. Remember my points, Riddle offer irrevelent bits of information meant to throw you off and BO's rule!

peace, the discussion ends here. Anyone else who responds with anything other needs to keep reading my posts over and over and dont make yourself look any more ignorant that you already have. OK great. I am more than qualified to answer this question, I do not need to waive my credentials in everyones' faces because my points are to the point. Please do not make yourself look stupid by continuing this post with "no it wont take off" because you are wrong, Regis that is my "final answer"

Tron Bo

knoxville, TN

Fireball 5k, Team Champions 3 years running

Team "BO"

thechamelion wrote:

the reason planes have to go 150+ mph to take off is so that they get 150+ miles of wind resistance on the wings to be able to lift the plane. the way a plane works is that the top of the wings are arched so that the air goes faster, making the air molecules more thin, then the dense air molecules below the wings push up on the wings which is how a planes gets its lift. On a treadmill the wind resistance would be 0 mph, and their would be no lift. so the answer is no.

The technical term you're looking for is the Bernoulli principle. How do air molecules get "more thin"?

The upper surface of an aerfoil is curved. The air accelerates over it. The increase in airspeed reduces the pressure. This creates lift. To demonstrate this get a piece of A4 paper. Hold one end tightly under your lower lip. Let the other end hang freely. Blow hard. The air you are blowing travels over the upper surface of the paper only.

Forget runners on treadmills, or cars. A car drives its wheels; a runner "drives" his legs. A planes exerts force on the air. Everything else is irrelevant. The plane will fly. The treadmill is a red herring. It can match the plane's speed, but it cannot hold the plane in place. The wheels freewheel.

OMG!!!!

I thought a lot of people on here were dumb, but this thread is shocking.

THE PLANE WILL TAKE OFF

Only two things to understand in this problem: (forget all the relative speed bs)

1) The plane's propulsion is the engines acting on the air (not the ground)

2) The speed of the wheels has very negligable influence on the speed of the plane. I'd love to write an essay on the wonders of the wheel but in short, the idea is that a wheel is nearly FRICTIONLESS. Any force the ground's (belt's) speed has on the rubber of the wheel is nullified by the wheel.

THE PLANE WILL TAKE OFF!!!!

THE PLANE WILL TAKE OFF!!!!

THE PLANE WILL TAKE OFF!!!!

THE PLANE WILL TAKE OFF!!!!

THE PLANE WILL TAKE OFF!!!!

Something that is being missed!!!

The plane will not take off from the treadmill, unless the treadmill is the length of a runway, which would then allow the plane to accelerate as normal and take off as normal.

If the treadmill is only long enough for the plan to fit on, then as soon as it starts moving forward relative to the ground, it will drop of the front because it lacks the airspeed necessary to create lift.

The assumption that I make is that the treadmill is an airplane sized treadmill, therefore the plane will not take off cause it does not have any space to accelerate.

Almost at The Edge

Perhaps an example to get people thinking!!

Think of a set of cycling rollers, the ones where when you pedal it sets the rear rollers going, which in turn makes the front roller spin so the you can steer. With this system you can pedal like crazy and hit some high speeds relative to the rollers, and can sometimes get quite out of control.

Now picture you get spinning at 30mph - what happens if you slide off the side of the rollers?? Do you go forward at 30 mph?? or do you stop stationary??

Answer = You stop because you have no forward momentum relative to the ground.

Now that you've done the simple one, now think of riding around a cycling velodrome. Imagine going around the corners at 30mph, and think of the lean you'd have to have to prevent yourself from going off the track.

Now, back to the rollers, pedalling at 30 mph, NOW LEAN - shit you fall off because you have no centrafugal forces working against you.

These examples correlate to the airplane example. In order to lean on a bike and not fall off, you need something pushing back on you. In order for a plane to take off, and not simply fall off the front of the treadmill, you need airflow over the wings to create lift.

Almost at The Edge

The plane will fly.

People seem to be confusing Air Speed with Ground Speed and misusing the word 'Speed'. The examples given by IT WILL FLY are spot on and outline the fact that the plane exerts force (thrust) on a matter completely inconnected with the ground speed (treadmill). This is the same as the boy on the skateboard being towed by the car off the treadmill.

The Aerospace fella uses such obviously wrong logic that he is either a liar or should be investigated in connection with every single plane crash to ensure he hadn't laid a finger on any of them.

thrust from the engines makes a plane move FORWARD

air moving over the wings makes it move UPWARD.

all the thrust in the world won't make it fly if air isn't moving over the wings

the treadmill moving backwards keeps the plane stationary

the air is not moving over the wings.

the plane will not fly

case closed

go home.

for all of you who say this damned plane will take off, go to the mall RIGHT now and try this:

go to the top of an escalator.

start to walk down the one that is going up (push people aside if necessary)

try to get to the bottom, while only walking AS FAST as the escalator is going UP.