btw

Dad-O-Lot ftw

actually Dad-a-lot FTMFL

it takes off and has no problem doing so

Now Cope

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Imagine one of the “people-mover” conveyor type walkways you see in large airports is set to move at a constant speed of 5 MPH.

Imagine also, a guy strapped to a skateboard using a powerful fan as his only propulsion. He has the fan set to move him at a constant 5 MPH.

If fan-propulsion-skateboard-guy is on the conveyor, facing opposite the direction of movement of the conveyor, does he move? (in relation to the area outside the conveyor)

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In the scenario above, does fan-propulsion-skateboard-guy move?

edit--add

[This message has been edited by Dad-O-Lot (edited 12/6/2006 12:42p).]

It depends on how much resistance the wheels provide....at that slow speed who knows? I think it would probably move slightly backwards in that situation....

I would like to add that I JUST woke up after a benadryl nap and am still very groggy (this is my excuse if I make some giant errors in what I am saying)

[This message has been edited by CopeIt (edited 12/6/2006 12:50p).]

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I would like to ass that

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giant mistake

Assuming no friction in the wheel bearings. (this is only an imaginary scenario after all).

In this scenario, the plane would definitely take off.

Assuming no friction? You know...I thought about it a little more in my state and I am just not sure about that scenario. If it is already at speed when it comes onto the conveyor it might not go anyhwere but I would like to say that it does still move forward. Can't exactly visualize in my head at the moment

Dad, why will it take off in that picture but not in the original question?

Just change the connected pulley belt system to an infinitely long conveyor belt that still miraculously matchs the speed of the plane.

By being attached to the conveyor like it is, the problem is drastically changed.

In order for the conveyor to move, the plane's distance from the pulley must change. That defines a forward movement relative to a stationary point. By having that definition as part of the problem, the consideration of whether or not the plane moves relative to the area around it is no longer an issue. The plane does move so it can takeoff.

The picture is drastically different from that which the original problem defined.

Draw a free body diagram of that picture and the original question. The forces on the plane are the same, if the pulley and belt are truely frictionless. It is the same question.

I will never draw a free body diagram in my free time. I swore myself to that after finishing both physics and have held true to my word. Luckily we are on the same page.

The forces are not the same.

In the picture, the plane and the conveyor may be moving at the same rate, but the wheels of the plane are actually spinning at twice that rate.

By introducing the pulley as a fulcrum, you have added another item to the equation in which it can be proven that for anything to move, the plane's distance from the pulley must change. The plane contacts (and provides forces to/from) the conveyor in both a vertical direction (the wheels) and a horizontal direction (attached to the back of the plane). In the original question, I assumed the only force between the conveyor and the plane was vertical (at the wheels).

dad-o-lot have you read the ENTIRE thread?

polpunk's post? (2nd post page 5)

you just seem obstinate. the plane flies.

Cecil is wrong!

Rope analogies on treadmills etc... do not match the stated question.

See again the "fan-propulsion-guy-on-a-skateboard" a few posts up. Tell me, does fan-propulsion-guy move?

I may be obstinate but that is only because I am right.

you are wrong

The plane flys.

The conveyor belt is moot.

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the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward.

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This is Cecil's error. The conveyor is the ground in this scenario. So, yes, the plane is moving in relation to the ground/conveyor but is NOT moving in relation to the air. Where the plane gets it's propulsion is actually irrelevant in this scenario.

Who is this Cecil Adams guy anyway? He should turn in his degree.

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horizontal direction (attached to the back of the plane).

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This force doesn't exist if the pulley and belt to the ground are frictionless. ( at least no more that normal drag on the plane)

[This message has been edited by Old Faithful (edited 12/6/2006 1:46p).]

The plane would react to normal ground pretty much the same as the conveyor. The conveyor is moot not the air flow.

The rpm of the wheels will reflect the forward motion of the plane plus the speed of the conveyor belt.

The only thing that will profoundly change is the speed of the wheels.

Dad-a-lot should turn in his degree AND his kids. I wouldnt want my dad to be this arrogantly wrong and think he can teach me......imagine the sex talk!?!?!

IIIhorn

In this situation:

Imagine one of the “people-mover” conveyor type walkways you see in large airports is set to move at a constant speed of 5 MPH.

Imagine also, a guy strapped to a skateboard using a powerful fan as his only propulsion. He has the fan set to move him at a constant 5 MPH.

If fan-propulsion-skateboard-guy is on the conveyor, facing opposite the direction of movement of the conveyor, does he move? (in relation to the area outside the conveyor)

Does the guy on the skateboard move?

If the wheel axels are frictionless (since you are only talking 5 mph) yes.

The wheels will rotate approximately twice as fast.

I am not at all comfortable with the "strap on" scenario described above. Let's keep this PG, folks!

Speed velocity in relation to ground: 5 mph.

Resulting speed velocity in relation to conveyor belt is now 10 mph in your scenario.

It's easier to understand in this scenario:

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Visualize it this way.

A conveyor belt is moving southward at 20 mph. You have attached a wagon to a wench which would pull the wagon across the ground at 20 mph. Set the wagon 50' from the south end of the conveyor belt. Turn on wench. The wagon will proceed across normal ground at 20 mph and then onto the conveyor belt. I assure you the wagon will proceed northward and reach the north end of the belt without problem.

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Thank You Horn.

You are still wrong.

By introducing the winch, you are introducing another factor, that being a definition of a change in distance between the wagon/plane and a fixed point. This factor does not exist in the original question.

By forcing the change in distance as part of the problem you have mutually exclusive assumptions.

Reading your answer to the skateboard-fan-guy scenario tells me all I need to know.

Thanks.

Obstinate and wrong is the same thing as fat, drunk and stupid. Its no way to go through life.

go attempt to teach your kid about the birds and bees. Watch him get confused and correct you......that is all I need to know

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Reading your answer to the skateboard-fan-guy scenario tells me all I need to know.

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Wow,

That was kinda harsh.

I guess I could say the same thing about your understanding of the application of external forces.

Sorry Horn,

I didn't mean to be harsh.

I'm done. I didn't realize anyone would take this personally.

Ouch!

Hey Dad-O-Lot,

I never regret participating in an intelligent discussion.

Great job!