WolstonFlyer Posted October 16, 2016 Author Share Posted October 16, 2016 It is an interesting video because you can see at one point that he speeds up the belt without altering the throttle position and the plane stays in the same relative position on the belt, the wheels just speed up to match. The forward thrust from the plane only needs to be enough to overcome the friction from the wheels / axles. When he does then increase the throttle and the plane moves forward relative to the belt, the wheels clearly won't suddenly start skidding forwards, so the wheel is still in contact with the belt, but for the bwheel to move forwards in relative position it must be covering more forwards distance than the belts backwards distance in the same time? Does that mean the wheel is going faster than the belt? I really should not have posted this question on here... sorry! Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by WolstonFlyer on 16/10/2016 21:19:29: It is an interesting video because you can see at one point that he speeds up the belt without altering the throttle position and the plane stays in the same relative position on the belt, the wheels just speed up to match. The forward thrust from the plane only needs to be enough to overcome the friction from the wheels / axles. When he does then increase the throttle and the plane moves forward relative to the belt, the wheels clearly won't suddenly start skidding forwards, so the wheel is still in contact with the belt, but for the bwheel to move forwards in relative position it must be covering more forwards distance than the belts backwards distance in the same time? Does that mean the wheel is going faster than the belt? I really should not have posted this question on here... sorry! Don't apologise - we've all enjoyed it. Got any more like it? Quote Link to comment Share on other sites More sharing options...
Mike Blandford Posted October 16, 2016 Share Posted October 16, 2016 Back to the physics! What is the "speed of the wheels"? It seems to me there is a misconception by many to this question. The only meaningful answer to this is "the speed of the axle" (equals the average speed of all parts of the wheel and tyre). Many seem to be assuming the conveyor belt is moving at the speed of the tyre where they contact each other. It is a fact that, for a wheel rolling along a stationary surface without slipping, the point of contact of the wheel to that surface is also stationary. So, for those that are assuming the "speed of the wheels" is "the speed of the tyre where it contacts the belt", then the conveyor belt will be stationary whatever the speed of the 747! Mike. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by ted hughes on 16/10/2016 20:53:47: Gary, he is missing the point. He is matching the belt speed with the aircraft speed! The original question is not concerned with the speed of the plane (in fact it remains stationary!) It is concerned with the speed of the wheels! For the sake of the hypothetical question, we are ignoring the effects of friction, physics,etc. It is a logic question. It is cheating to change the terms of the question. Edited By ted hughes on 16/10/2016 20:55:40 But I can see the wheels remaining stationary (with the aircraft) and then moving from left to right and back again as the throttle is increased and reduced. Edited By Gary Manuel on 16/10/2016 21:41:18 Quote Link to comment Share on other sites More sharing options...
Phil 9 Posted October 16, 2016 Share Posted October 16, 2016 maybe it is not a question of physics but a question of wording and the interpretation of the wording. I shall ask my lawyer Edited By Phil 9 on 16/10/2016 21:47:31 Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by Stuart Coyle on 16/10/2016 19:37:27: The model on the conveyor belt demonstrates Coulomb's law of friction, indicating that the u/c wheel has a plain bearing (hole with a bit of piano wire). I didn't know about THIS, so I have actually learnt something about physics. Funny thing is, I can relate this to the real world. If you try to pull a log along the ground, it takes an awful lot of effort to get it moving, but once it's moving, it will keep going and you can even run with it without putting much extra effort in. Strange how mother nature is sticking to the laws of physics. She must have known what they would be! Edited By Gary Manuel on 16/10/2016 21:52:50 Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted October 16, 2016 Author Share Posted October 16, 2016 I am glad you have enjoyed it Gary! Well there is one about a quad copter, it takes off and hovers inside a car that has its windows rolled down, while the car drives up to 30mph, the quad then flies out of the side window of the car, does it keep pace with the car so it can fly back in again or suddenly drop behind the car..? Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by Mike Blandford on 16/10/2016 21:40:42: Back to the physics! What is the "speed of the wheels"? It seems to me there is a misconception by many to this question. The only meaningful answer to this is "the speed of the axle" (equals the average speed of all parts of the wheel and tyre). Many seem to be assuming the conveyor belt is moving at the speed of the tyre where they contact each other. It is a fact that, for a wheel rolling along a stationary surface without slipping, the point of contact of the wheel to that surface is also stationary. So, for those that are assuming the "speed of the wheels" is "the speed of the tyre where it contacts the belt", then the conveyor belt will be stationary whatever the speed of the 747! Mike. Yep. That's what I was trying to say a few pages ago. Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 16, 2016 Share Posted October 16, 2016 Posted by Gary Manuel on 16/10/2016 21:40:45: Posted by ted hughes on 16/10/2016 20:53:47: Gary, he is missing the point. He is matching the belt speed with the aircraft speed! The original question is not concerned with the speed of the plane (in fact it remains stationary!) It is concerned with the speed of the wheels! For the sake of the hypothetical question, we are ignoring the effects of friction, physics,etc. It is a logic question. It is cheating to change the terms of the question. Edited By ted hughes on 16/10/2016 20:55:40 But I can see the wheels remaining stationary (with the aircraft) and then moving from left to right and back again as the throttle is increased and reduced. Edited By Gary Manuel on 16/10/2016 21:41:18 Yes I know they remain stationary with respect to the plane, but they rotate at a variable speed (the speed at which the belt moves). Quote Link to comment Share on other sites More sharing options...
Mike Blandford Posted October 16, 2016 Share Posted October 16, 2016 Posted by ted hughes on 16/10/2016 20:08:55: No matter how fast the man on the treadmill runs he will always stand still (because the treadmill always matches his speed). But if he will "always stand still" then his speed is zero, so the treadmill is also stationary if it matches his speed! Mike. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by ted hughes on 16/10/2016 21:56:42: Posted by Gary Manuel on 16/10/2016 21:40:45: Posted by ted hughes on 16/10/2016 20:53:47: Gary, he is missing the point. He is matching the belt speed with the aircraft speed! The original question is not concerned with the speed of the plane (in fact it remains stationary!) It is concerned with the speed of the wheels! For the sake of the hypothetical question, we are ignoring the effects of friction, physics,etc. It is a logic question. It is cheating to change the terms of the question. Edited By ted hughes on 16/10/2016 20:55:40 But I can see the wheels remaining stationary (with the aircraft) and then moving from left to right and back again as the throttle is increased and reduced. Edited By Gary Manuel on 16/10/2016 21:41:18 Yes I know they remain stationary with respect to the plane, but they rotate at a variable speed (the speed at which the belt moves). The belt doesn't rotate - it moves in a linear manner. The same speed but opposite direction to the wheel, which is attached to the plane etc etc etc Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 16, 2016 Share Posted October 16, 2016 Posted by Mike Blandford on 16/10/2016 22:10:28: Posted by ted hughes on 16/10/2016 20:08:55: No matter how fast the man on the treadmill runs he will always stand still (because the treadmill always matches his speed). But if he will "always stand still" then his speed is zero, so the treadmill is also stationary if it matches his speed! Mike. That is semantics. "Stands still" relates to his position on the treadmill, not that he isn't moving- as I suspect you know. The "man" is used figuratively for illustration- he doesn't have wheels. Several people here have referred to a "man on a treadmill"- it is a device to explain what the plane does, it is not literal. It is like explaining gravity in terms of an apple falling-it is very doubtful that Newton actually was in an orchard when he came up with his theory of gravity, he was more likely peering at the heavenly bodies (when he wasn't poking needles in his eye). It is very difficult to make any headway on this thread, as there are constant red herrings imposed with regard to matters of friction, bearings, semantics, etc. The question is one purely of logic. Edited By ted hughes on 16/10/2016 22:25:32 Quote Link to comment Share on other sites More sharing options...
The Wright Stuff Posted October 16, 2016 Share Posted October 16, 2016 I think the UK should hold a referendum on this. The physicists, aeronautical engineers and a Professor of mechanical engineering have patiently explained the problem multiple times. Sounds like we've all had enough of the experts! Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by The Wright Stuff on 16/10/2016 22:28:25: I think the UK should hold a referendum on this. The physicists, aeronautical engineers and a Professor of mechanical engineering have patiently explained the problem multiple times. Sounds like we've all had enough of the experts! But the scots would want a second referendum! Quote Link to comment Share on other sites More sharing options...
Mike Blandford Posted October 16, 2016 Share Posted October 16, 2016 Ted: What do you understand by "the speed of the wheels"? (You might look up the term "cycloid" before you answer). Mike. Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 16, 2016 Share Posted October 16, 2016 Imagine it this way: The plane sits on the belt. The belt starts to move backwards slowly. The plane won't move - its wheels will turn, but because of the absence of friction, the fuselage will remain stationary. Open the belt to 1000kph , and the plane still won't move. It wheels will turn faster though. Stop the belt and open the plane's throttles. The plane will start to move forwards, and the belt will start to move backwards at increasing speed to match the speed of the plane. However, we have already demonstrated that the movement of the belt does not affect the fuselage, which is getting its thrust quite independently from the belt (unlike the running man, who is using the backwards-moving belt to provide his impetus). Therefore, there is no reason why the plane should not take off as normal. Edited By ted hughes on 16/10/2016 22:46:23 Quote Link to comment Share on other sites More sharing options...
Mannyroad Posted October 16, 2016 Share Posted October 16, 2016 I can't believe this thread has run so long. As has already been stated many times, the planes engines provide thrust that will move it forwards THROUGH THE AIR. The wheels, being in contact with the ground, acting merely as free rolling castors that support the aircraft of the belt. As the aircraft moves forward through the air, by the thrust of the engines, the wheels will spin at whatever rotational speed they need to in order that the distance travelled around their circumference matches precisely that of the belts speed. Effectively, the wheels are at standstill, the engines run up and the plane moves forwards through the air at an accelerating velocity and the wheels and the belt gain velocity (rotational for the wheels/ linear for the belt by a corresponding amount, in each case starting at zero. Its not a case of the wheels can't move forwards. They do. Its a case of while the wheels DO move forwards, the belt is, by the nature of the question, is forced to RESPOND, by increasing in speed. BUT, this does not alter the fact that the wheels will move as the aircraft does. The belt is slave to the rotational velocity of the wheels, given the question. Surely this is obvious. So yes, of course the plane will take off Edited By Mannyroad on 16/10/2016 22:54:50 Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by ted hughes on 16/10/2016 22:45:22: Imagine it this way: The plane sits on the belt. The belt starts to move backwards slowly. The plane won't move - its wheels will turn, but because of the absence of friction, the fuselage will remain stationary. Open the belt to 1000kph , and the plane still won't move. It wheels will turn faster though. Stop the belt and open the plane's throttles. The plane will start to move forwards, and the belt will start to move backwards at increasing speed to match the speed of the plane. However, we have already demonstrated that the movement of the belt does not affect the fuselage, which is getting its thrust quite independently from the belt (unlike the running man, who is using the backwards-moving belt to provide his impetus). Therefore, there is no reason why the plane should not take off as normal. Edited By ted hughes on 16/10/2016 22:46:23 Ted. You've finally got it!!!!! I can't fault anything you've said here. Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted October 16, 2016 Author Share Posted October 16, 2016 Perhaps it is time to close this thread, it has gone on far too long! Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted October 16, 2016 Share Posted October 16, 2016 At the top of the rotation the wheel is moving forward, the direction of the plane. At the bottom it is going backwards, the direction of the conveyor. The axle is always stationary relative to the plane and moves with it, not with the conveyor. Therefore if the plane is going forward at a ground speed (in still air the same as the air speed) of 150 mph and the conveyor is going backwards at 150 mph, the difference between the two is 300 mph and the vector is the plane going forwards relative to the ground. The wheels always rotate at a speed that is a function of the plane and the conveyor together. One or both can be moving or stationary, the wheel rotation speed will always be the sum of the two. The plane always achieves flying speed relative to the ground whether the conveyor is standing still, doing 50, 100 or whatever other speed, as long as the brakes are off and the engines running. If the brakes are on the wheels won't be rotating at all and the plane will move backwards unless engine thrust overcomes the braking force. The wording of the question means that the brakes must be off, therefore this is the only thing that can happen. Quote Link to comment Share on other sites More sharing options...
Mike Blandford Posted October 16, 2016 Share Posted October 16, 2016 Ted: I thought from your earlier posts you didn't think the 747 would take off, hence my question. Mike. Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 16, 2016 Share Posted October 16, 2016 Posted by Gary Manuel on 16/10/2016 22:55:15: Posted by ted hughes on 16/10/2016 22:45:22: Imagine it this way: The plane sits on the belt. The belt starts to move backwards slowly. The plane won't move - its wheels will turn, but because of the absence of friction, the fuselage will remain stationary. Open the belt to 1000kph , and the plane still won't move. It wheels will turn faster though. Stop the belt and open the plane's throttles. The plane will start to move forwards, and the belt will start to move backwards at increasing speed to match the speed of the plane. However, we have already demonstrated that the movement of the belt does not affect the fuselage, which is getting its thrust quite independently from the belt (unlike the running man, who is using the backwards-moving belt to provide his impetus). Therefore, there is no reason why the plane should not take off as normal. Edited By ted hughes on 16/10/2016 22:46:23 Ted. You've finally got it!!!!! I can't fault anything you've said here. The puzzle of the plane on the belt was discussed in my "O" level physics class 40 odd years ago! Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted October 16, 2016 Share Posted October 16, 2016 Posted by ted hughes on 16/10/2016 22:59:34: The puzzle of the plane on the belt was discussed in my "O" level physics class 40 odd years ago! Which side of the argument were you supporting back then? Quote Link to comment Share on other sites More sharing options...
ted hughes Posted October 16, 2016 Share Posted October 16, 2016 Posted by Gary Manuel on 16/10/2016 23:02:55: Posted by ted hughes on 16/10/2016 22:59:34: The puzzle of the plane on the belt was discussed in my "O" level physics class 40 odd years ago! Which side of the argument were you supporting back then? The most amusing. Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted October 16, 2016 Author Share Posted October 16, 2016 I am sure the EU have re-written the laws of physics since then, they like to do things like that for no reason 😂 Quote Link to comment Share on other sites More sharing options...
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