Plane on a Treadmill

[cmoneyr]

So science teacher, you still haven't answered the question...... What force is acting on the plane and how, in order to cancel out the thrust of the engines and thus deter it's forward motion. Try to give us something a little deeper than, "the treadmill is doing it." Attempt to explain the "HOW" of your conclusion.

I'd like to hear htown's answer to that as well. He seems completely certain that the plane won't move, but has no reasoning to back it up other than, "but it's on a treadmill!".

 

[mjlane]

The belt is moving at exactly the same speed as the plane, in the opposite direction. EVERY example around the internet has this included, that the belt is set up to always move at the same speed of the plane but in the opposite direction, so when the plane speeds up, the belt also speeds up. The plane is NEVER moving forward relative to a non-moving reference point.

Think of it this way:

If the plane was sitting on the treadmill with the engines completely off and the treadmill running at 30 mph, what is the plane doing? Assuming no friction, the plane is stationary since the wheels are free to turn. The wheels of the plane are travelling at 30 mph, but the plane is going 0 mph in relation to a fixed reference point.

Now, let's just say that you gave the plane a push with a very large hand (jet engine). What would happen to the plane? Would it continue to sit still or would it move forward? Of course, it would move forward at a speed equal to the amount of force. Increase the force/thrust, and you will increase the speed.

The speed of the plane and the speed of the plane's wheels are most definitely NOT equal. This seems to be the point at which you are stymied.

 

[CloneFan65]

This video might help:

[ame="http://www.youtube.com/watch?v=NINJQ5LRh-0"]YouTube - ok go[/ame]

Or not.

 

[Cloned4Life]

I posted this earlier...

The wheels and the treadmill have nothing to do with it. Visualize a plane that can magically hover above the treadmill with no wheels at the same height as a plane with wheels. The hovering provides no lift or thrust. It just keeps the plane off the ground and allows for free movement forward and backwards. Turn on the treadmill. Fire up the engines. As the plane goes faster forward, the treadmill goes the same speed backwards. In this case, does the treadmill have any affect on the plane? I assume you'll say no. The hovering allows for free movement and decouples the plane from the motion of the treadmill. Now add the wheels back in. The wheels do what? They allow for free movement and decouple the plane from the treadmill; the same as the magic hovering situation.

Without reading through all these posts, I like this one. Makes sense to me.

 

[htownclone]

I'd like to hear htown's answer to that as well. He seems completely certain that the plane won't move, but has no reasoning to back it up other than, "but it's on a treadmill!".

Wow, you guys are incredible...when did I ever say, "but it's on a treadmill" to explain my reasoning.

You continue to talk about the thrust overcoming the friction, etc, which is really a fancy way of saying the plane's speed will increase.

If the plane's speed increases, then the belt will also increase, which will keep the plane in a stationary position to a reference point.

Or I suppose I could have just said, "but it's on a treadmill" cause that's my favorite argument.

 

[ISUFan22]

What kind of jets? No one thought of the planes with the jets that propel the plane off the ground vertically? Methinks this would have no problem... :wink:

 

[htownclone]

I posted this earlier...

The wheels and the treadmill have nothing to do with it. Visualize a plane that can magically hover above the treadmill with no wheels at the same height as a plane with wheels. The hovering provides no lift or thrust. It just keeps the plane off the ground and allows for free movement forward and backwards. Turn on the treadmill. Fire up the engines. As the plane goes faster forward, the treadmill goes the same speed backwards. In this case, does the treadmill have any affect on the plane? I assume you'll say no. The hovering allows for free movement and decouples the plane from the motion of the treadmill. Now add the wheels back in. The wheels do what? They allow for free movement and decouple the plane from the treadmill; the same as the magic hovering situation.

So you are saying that if a plane were on a treadmill...or we can just simplify and say an RC car is on a normal sized treadmill and the treadmill was turned on, the car would stay in place and not move backwards?

 

[twittkop]

So you are saying that if a plane were on a treadmill...or we can just simplify and say an RC car is on a normal sized treadmill and the treadmill was turned on, the car would stay in place and not move backwards?

For the 300th time...cars and planes don't apply force in the same way to move forward.

 

[htownclone]

For the 300th time...cars and planes don't apply force in the same way to move forward.

Excellent job answering my question. I feel as though maybe I'm the only one on this thread who graduated from ISU and the rest of you must have graduated from Iowa.

 

[ISUFan22]

Excellent job answering my question. I feel as though maybe I'm the only one on this thread who graduated from ISU and the rest of you must have graduated from Iowa.

Thems be fightin' words right there...you're on your own...

 

[CloneFan65]

So you are saying that if a plane were on a treadmill...or we can just simplify and say an RC car is on a normal sized treadmill and the treadmill was turned on, the car would stay in place and not move backwards?

If the wheels were free turning with no friction, then yes.

 

[mjlane]

So you are saying that if a plane were on a treadmill...or we can just simplify and say an RC car is on a normal sized treadmill and the treadmill was turned on, the car would stay in place and not move backwards?

Well, it's a little different with a car, but assuming the wheels are able to rotate freely and excepting friction, then Yes. It's the same as the example given where you are standing on a treadmill wearing rollerskates. Assuming no friction, you won't move an inch no matter how fast the treadmill is running.

 

[cmoneyr]

Excellent job answering my question. I feel as though maybe I'm the only one on this thread who graduated from ISU and the rest of you must have graduated from Iowa.

I feel as though there was a huge teacher shortage in Houston and they took all comers.

 

[cmoneyr]

If the plane's speed increases, then the belt will also increase, which will keep the plane in a stationary position to a reference point.

Yes, as the plane moved faster so would the belt, BUT, the only affect it would have is that the wheels would have to spin faster, it would have no effect on the speed of the plane.

 

[htownclone]

Well, it's a little different with a car, but assuming the wheels are able to rotate freely and excepting friction, then Yes. It's the same as the example given where you are standing on a treadmill wearing rollerskates. Assuming no friction, you won't move an inch no matter how fast the treadmill is running.

THERE IS FRICTION!!!! HOW ARE WE SAYING THAT THERE ISN'T FRICTION!?!?!?!?!? WHERE DID IT GO????

 

[acs4isu]

Is anyone else amazed that this has gone on for 34 pages?

 

[twittkop]

Ft = Force from thrust
FD = Force of drag
Ff = Force of friction

For a plane to takeoff from a runway or treadmill Ft > FD + Ff. Ff = μFn. μ is the coefficient of friction and Fn is the normal force of the runway/treadmill on the planes landing gear.

Please explain how increasing the speed of the treadmill will increase the force of friction, thus preventing the plane from moving forward in relation to the ground.

 

[CloneFan65]

THERE IS FRICTION!!!! HOW ARE WE SAYING THAT THERE ISN'T FRICTION!?!?!?!?!? WHERE DID IT GO????

I explained it like this earlier in the discussion. Let's do everything at constant rates. We'll set the plane at 100 mph, propelled by the friction of the jets against the air. We'll set the treadmill at 100 mph in the opposite direction. If we set the jet on the treadmill, the jet will travel 100 mph forward in relation to the ground, but the wheels will spin at 200 mph. (To make you happy we'll account for friction and say the jet travels 98 mph forward, but it will still travel forward.)

 

[mjlane]

THERE IS FRICTION!!!! HOW ARE WE SAYING THAT THERE ISN'T FRICTION!?!?!?!?!? WHERE DID IT GO????

Fine, there's friction. So instead of the plane/RC car/person on roller skates being motionless, they are now moving backward at a very slow rate. Now if you apply a very small amount of force in the forward direction, you will easily over come the force of friction.

It really can't be explained any simpler than that, and if you can't understand that, then I can't help you.

 

[htownclone]

Ft = Force from thrust
FD = Force of drag
Ff = Force of friction

For a plane to takeoff from a runway or treadmill Ft > FD + FfFf = μFn. μ is the coefficient of friction and Fn is the normal force of the runway/treadmill on the planes landing gear.

Please explain how increasing the speed of the treadmill will increase the force of friction, thus preventing the plane from moving forward in relation to the ground.

Cool, lets all just go copy and paste formulas from wikipedia that we don't understand.

Please explain to me how the plane can move faster than the belt if they are moving at the same speed.