Originally posted by: smack Down
Originally posted by: LTC8K6
Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?
I think we do.
So let's take the same car and attach a jet engine to it.
Now let's put the car back on the treadmill, but do not start up the jet engine.
So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.
Let's say the car's max is 110MPH.
So we have the car on the treadmill at WOT.
The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.
Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.
The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.
The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.
The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.
The plane will easily take off on the treadmill that matches it's forward speed.
Sorry but weather a force is applied via the wheels or jet makes no difference. Draw a free body diagram and guess what in both case the force is applied to the body of the car.
Originally posted by: Quintox
It's on TV now
Originally posted by: Fenixgoon
i see this thread has not gone anywhere. surprise surprise
Originally posted by: spidey07
Originally posted by: Fenixgoon
i see this thread has not gone anywhere. surprise surprise
And neither has the plane.
For if it did, the bounds of the problem have been broken.
Originally posted by: spidey07
Originally posted by: Fenixgoon
i see this thread has not gone anywhere. surprise surprise
And neither has the plane.
For if it did, the bounds of the problem have been broken.
Originally posted by: spidey07
Originally posted by: Fenixgoon
i see this thread has not gone anywhere. surprise surprise
And neither has the plane.
For if it did, the bounds of the problem have been broken.
The wheels of a car are not free spinning. A car moves by applying force at the wheels to the ground (or in this case, the treadmill).
Originally posted by: LTC8K6
The wheels of a car are not free spinning. A car moves by applying force at the wheels to the ground (or in this case, the treadmill).
her209, exactly what part of my post made you think I didn't know why a car moves?
because you seem to ignore it when looking at a plane?
Originally posted by: LTC8K6
because you seem to ignore it when looking at a plane?
You lost me.
What am I ignoring?
Originally posted by: sao123
Originally posted by: smack Down
Originally posted by: LTC8K6
Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?
I think we do.
So let's take the same car and attach a jet engine to it.
Now let's put the car back on the treadmill, but do not start up the jet engine.
So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.
Let's say the car's max is 110MPH.
So we have the car on the treadmill at WOT.
The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.
Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.
The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.
The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.
The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.
The plane will easily take off on the treadmill that matches it's forward speed.
Sorry but weather a force is applied via the wheels or jet makes no difference. Draw a free body diagram and guess what in both case the force is applied to the body of the car.
bad grammer... bad spelling... and bad physics...
Go away.
Originally posted by: smack Down
Originally posted by: sao123
Originally posted by: smack Down
Originally posted by: LTC8K6
Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?
I think we do.
So let's take the same car and attach a jet engine to it.
Now let's put the car back on the treadmill, but do not start up the jet engine.
So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.
Let's say the car's max is 110MPH.
So we have the car on the treadmill at WOT.
The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.
Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.
The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.
The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.
The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.
The plane will easily take off on the treadmill that matches it's forward speed.
Sorry but weather a force is applied via the wheels or jet makes no difference. Draw a free body diagram and guess what in both case the force is applied to the body of the car.
bad grammer... bad spelling... and bad physics...
Go away.
Who cares about grammer and spelling by the way you spelled grammar wrong.
AS for the physics lets pretend that we have two cars that have the same mass(m), same moment of inertia(i), and no friction. For the sake of simplicity lets take the acceleration at 1 m/s/s
On a road do you agree that they would reach a speed of 1 m/s after one second of driving? and both have the same amount of kinetic energy? 1 * m + 1 * i
Ok now lets put our two cars on the same treadmill. Your theory is the the rocket car will still accelerate at 1 m/s/s (or some other value greater then zero) and the engine car will accelerate at 0 m/s/s (that is stay in place). Correct? Additional you claim that the treadmill will be going backwards at a minimum of 1 m/s/s (In reality it would be going faster then this. The speed depends on the mass of the car. 1 m/s/s is only true with a car of zero mass.)
The rocket car energy is 1 * m + i * (1 + Vtreadmill)^2.
The normal car has an energy is 0 *m + i * Vtreadmill^2
Remember that in the 1 second on the road they had the same energy and now the rocket car has much more energy when both are required to be equal and equal to the original 1 * m + 1 * i. There is no way a plane can behave differently then the car.
Originally posted by: smack Down
Originally posted by: sao123
Originally posted by: smack Down
Originally posted by: LTC8K6
Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?
I think we do.
So let's take the same car and attach a jet engine to it.
Now let's put the car back on the treadmill, but do not start up the jet engine.
So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.
Let's say the car's max is 110MPH.
So we have the car on the treadmill at WOT.
The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.
Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.
The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.
The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.
The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.
The plane will easily take off on the treadmill that matches it's forward speed.
Sorry but weather a force is applied via the wheels or jet makes no difference. Draw a free body diagram and guess what in both case the force is applied to the body of the car.
bad grammer... bad spelling... and bad physics...
Go away.
Who cares about grammer and spelling by the way you spelled grammar wrong.
AS for the physics lets pretend that we have two cars that have the same mass(m), same moment of inertia(i), and no friction. For the sake of simplicity lets take the acceleration at 1 m/s/s
On a road do you agree that they would reach a speed of 1 m/s after one second of driving? and both have the same amount of kinetic energy? 1 * m + 1 * i
Ok now lets put our two cars on the same treadmill. Your theory is the the rocket car will still accelerate at 1 m/s/s (or some other value greater then zero) and the engine car will accelerate at 0 m/s/s (that is stay in place). Correct? Additional you claim that the treadmill will be going backwards at a minimum of 1 m/s/s (In reality it would be going faster then this. The speed depends on the mass of the car. 1 m/s/s is only true with a car of zero mass.)
The rocket car energy is 1 * m + i * (1 + Vtreadmill)^2.
The normal car has an energy is 0 *m + i * Vtreadmill^2
Remember that in the 1 second on the road they had the same energy and now the rocket car has much more energy when both are required to be equal and equal to the original 1 * m + 1 * i. There is no way a plane can behave differently then the car.
Originally posted by: sao123
Originally posted by: smack Down
Originally posted by: sao123
Originally posted by: smack Down
Originally posted by: LTC8K6
Do we all agree that a car cannot move given the scenario of the treadmill matching it's speed?
I think we do.
So let's take the same car and attach a jet engine to it.
Now let's put the car back on the treadmill, but do not start up the jet engine.
So we are still the same. The car can't go anywhere because the treadmill is matching the car's speed up to it's max.
Let's say the car's max is 110MPH.
So we have the car on the treadmill at WOT.
The car's speedo says 110mph, the treadmill indicates 110mph, and the car is stationary with it's wheels rotating at about twice the speed they would be on the ground. There will be some slip, but it's irrelevant.
Now if we light off the jet, the car will move forwards because the jet is unaffected by the wheel speed, or the matching treadmill speed.
The treadmill will continue to match the car's forward speed right up until the car leaves the treadmill under the jet's thrust, but this will not stop the jet from pushing the car forwards.
The only thing the jet has to overcome to move the car are the small forces of inertia, wheel bearing friction, and wind resistance, which it will do easily.
The car with the jet engine, and a plane, can move forwards on a treadmill that matches their forward speed. There is nothing to stop them.
The plane will easily take off on the treadmill that matches it's forward speed.
Sorry but weather a force is applied via the wheels or jet makes no difference. Draw a free body diagram and guess what in both case the force is applied to the body of the car.
bad grammer... bad spelling... and bad physics...
Go away.
Who cares about grammer and spelling by the way you spelled grammar wrong.
AS for the physics lets pretend that we have two cars that have the same mass(m), same moment of inertia(i), and no friction. For the sake of simplicity lets take the acceleration at 1 m/s/s
On a road do you agree that they would reach a speed of 1 m/s after one second of driving? and both have the same amount of kinetic energy? 1 * m + 1 * i
Ok now lets put our two cars on the same treadmill. Your theory is the the rocket car will still accelerate at 1 m/s/s (or some other value greater then zero) and the engine car will accelerate at 0 m/s/s (that is stay in place). Correct? Additional you claim that the treadmill will be going backwards at a minimum of 1 m/s/s (In reality it would be going faster then this. The speed depends on the mass of the car. 1 m/s/s is only true with a car of zero mass.)
The rocket car energy is 1 * m + i * (1 + Vtreadmill)^2.
The normal car has an energy is 0 *m + i * Vtreadmill^2
Remember that in the 1 second on the road they had the same energy and now the rocket car has much more energy when both are required to be equal and equal to the original 1 * m + 1 * i. There is no way a plane can behave differently then the car.
the two examples are incomparable... 1 is rigid and has near 80% transfer rate, the other is not rigid and has close to 20% transfer rate. you cant just sum the vectors 1 to 1, you must equalize them first.
Take both cars again.
Put them at the top of a extremely long steep mountain, the car running on its engine will eventually reach a velocity where it will exceed the transmission will exceede the engine rotation velocity... This causes back compression (think jake brakes) in the engine which will limit its max velocity. the rocket car in neutral will never experience this, and will accelerate to terminal velocity.
so back to your treadmille example, if the treadmille would go faster than both the plane and the car, the car would move backwards faster than the plane because of the rigidity transfer. they do not indeed have the same energy sum because their transfer rates are not the same.
While the concept seems a bit counter-intuitive and difficult to grasp, but if you think about it thoroughly, it's actually quite obvious.Originally posted by: bigal40
I see someone calculating the force of friction that the plane would need to overcome using the coefficient of friction between rubber and asphalt but that is completely wrong.
Originally posted by: sao123
Originally posted by: astroidea
Originally posted by: Kev
Originally posted by: uclaLabrat
Originally posted by: astroidea
The plane takes of depending on which plane it is!
So the main argument that the plane would still take off is that there's no counter force keeping the plane from moving forward as the thrust of the plane is independent from the wheels. So as long as the wheels roll freely, the plane will still take off.
However, there is a counter force! Rotational friction. There is a frictional force in the bearings of the wheels. It does not roll completely freely without any opposing forces. The thrust force the plane puts out would be needed to counteract this frictional force.
Therefore, the quicker the wheels spin, the more force the plane would have to put out to spin the wheels.
But isn't the conveyer belt pushing the same amount of force on the wheels in the opposite direction?
So when would the plane actually move forward relative to the air?
Well first, let's imagine this situation:
The plane is on a conveyer belt that's moving backwards at 100mph. The plane is moving forwards at 100mph also. So right now, the plane isn't moving relative to the air right? But what would happen if the plane suddenly stopped all its engines? The coveyer belt would begin to move the plane backwards. It would no longer be able to maintain the static air speed.
Therefore, we can reasonably deduce that it does indeed take some force from the plane's thrust in order to counteract the motion of the conveyer belt.
So how much force would it take to keep the plane stationary with the air when the belt is moving backwards at 1000000000000 miles per hour? Would the plane have enough power to keep it stationary? Probably not.
But then again, is it even possible for the tires to still be in contact with the treadmill at 100000000000 miles per hour? According to newtonian physics, once the frictional force of the bearings exceed the frictional force between the tires and the surface of the conveyer belt, wouldn't the tires lose grip with the surface? Once the tires lose surface, the plane will only have to generate enough thrust to counteract the frictional force between the tires and the surface of the belt in order to move forward.
So therefore, the plane will move forward, but only when the plane is able to generate enough thrust for the friction of the tires to break free from the belt.
But is there any plane that has a powerful enough engine that can generate enough force to break free?
Let's look at the Boeing 777.
According to wikipedia, it generates 418,000N of thrust, and has a mass of 139,225kg.
The coefficient of static friction between tires and tarmac is about 0.7.
If you work out the math, µmg is (0.7)(139225)(9.8) = 956,058N.
This is over twice as much force as what the 418,000N of thrust the engines put out.
And if you consider the hundreds of opposing forces that I haven't accounted for, it's even less likely to be able to break free from the friction.
Thus, Plane DOESN'T TAKE OFF
But what if you had a plane with a better weight to thrust ratio?
Well, I let's look at the F22 Raptor.
According to wikipedia, the two turbofan engines generates a total of 311,000N of thrust. The plane when empty has a mass of 14,365kg.
So given that, let's work out the math again. (0.7)(14365)(9.8) = 98,544N
In this case, the 311,000N of thrust is significantly greater than 98,544N of frictional force. So in this case, the plane would take off!
In conclusion: THE PLANE MAY OR MAY NOT TAKE OFF DEPENDING ON WHICH PLANE IT IS!
OMG. Someone else understands friction and thrust!
How reassuring. Nice work on the analysis btw. Most coherent and lucid I've seen thus far.
And yet he's still wrong.
Oh really. Well why don't you enlighten us in how the argument is flawed.
:roll:
because the initial starting condition is impossible to achieve. The poster assumes to be true the exact argument he is trying to prove is possible.
Lets assume that his opening condition is true...
1)The conveyor belt is moving at velocity -X.
2)The plane is moving at velocity X with respect to the conveyor belt.
3)The entire conveyor system is not moving with respect to a universal fixed point, (for example: the atmosphere.) providing a ?D of 0 for the plane.
4)The plane exerts a force on and recieves a counter acceleration with respect to our universal fixed frame.
An object undergoing acceleration must have a ?V, and therefore a ?D cannot be 0...
Contradiction.
The problem is: This plane cannot be be stationary and in motion at the same time.