Page 4 of 5 FirstFirst 12345 LastLast
Results 61 to 80 of 97
  1. vw2002's Avatar
    Posts
    904 Posts
    Global Posts
    939 Global Posts
    #61  
    the great debate caught on film....

    I gotta have more cowbell
  2. vw2002's Avatar
    Posts
    904 Posts
    Global Posts
    939 Global Posts
    #62  


    case closed.
    I gotta have more cowbell
  3. #63  
    Quote Originally Posted by vw2002 View Post


    case closed.
    <IMG WIDTH="200" HEIGHT="50" SRC=http://www.visorcentral.com/images/visorcentral.gif> (ex)VisorCentral Discussion Moderator
    Do files get embarrassed when they get unzipped?
  4. #64  
    --
    Aloke
    Cingular GSM
    Software:Treo650-1.17-CNG
    Firmware:01.51 Hardware:A
  5. #65  
    Quote Originally Posted by aprasad View Post
    Most people in those discussions are sloppy about what "the conveyor belt matches the speed of the airplane" means. As mentioned many times now, if it means "conveyor belt matches the speed of the airplane relative to the ground/the air", the plane takes off.

    If it means "matches the speed of the plane relative to the conveyor belt", then the plane cannot move relative to the ground/air. Forward movement is only possible if the airplane moves faster than the conveyor belt rolls backwards, which would be in violation of "matches the speed of the conveyor belt", and hence not possible - not possible because of the conditions defined in "matches the speed of the plane relative to the conveyor belt".

    You, too, seem to be stuck in physics, which is not the issue. Of course it is possible for the airplane to move faster than a treadmill/conveyor belt from a physical point of view, but it is not possible according to the constraints of the problem in the version "conveyor belt matches the speed of the plane relative to the conveyor belt".

    The plane pushing forward would only lead to the treadmill going faster until the tires explode (again, only in version "conveyor belt matches the speed of the plane relative to the conveyor belt")

    Here are two questions: do you think it is physically possible that an airplane rolls at 5 mph relative to the treadmill surface which rolls at 5 mph into the other direction?

    If yes, what is the speed of that airplane relative to the ground?
    “Reality is that which, when you stop believing in it, doesn't go away.” (Philip K. ****)
  6. #66  
    Quote Originally Posted by clulup View Post
    Most people in those discussions are sloppy about what "the conveyor belt matches the speed of the airplane" means. As mentioned many times now, if it means "conveyor belt matches the speed of the airplane relative to the ground/the air", the plane takes off.

    If it means "matches the speed of the plane relative to the conveyor belt", than the plane cannot move relative to the ground air, because a forward movement is only possible if the airplane moves faster than the conveyor belt roll backwards, which would be in violation of "matches the speed of the conveyor belt", and hence not possible.
    Thats the whole problem of this issue, the scenario in question cannot really happen or the wording is too confusing to give a precise answer.

    So I suggest we leave it at that since this is otherwise going to be a fruitless discussion...
    (but I did enjoy the python scetches
    For python fans check this out:
    http://hightechnews.info/2006/11/30/...-monty-python/)
    <disclaimer this potentially will rob you of a lot of time >
    <IMG WIDTH="200" HEIGHT="50" SRC=http://www.visorcentral.com/images/visorcentral.gif> (ex)VisorCentral Discussion Moderator
    Do files get embarrassed when they get unzipped?
  7. #67  
    This has probably already been said, but I haven't read the entire thread from the beginning...

    The speed of the plane in relation to the treadmill means nothing... if no air is passing over the wings, the plane will never leave the ground.

    If the treadmill speed matches the speed that the plane would be moving down a runway, the plane is essentially standing still (as viewed by someone standing next to the treadmill), no air is passing over the wings, and it will not lift.

    If the treadmill can't keep up with the thrust of the engines, the plane will ultimately propel itself off the treadmill onto the ground where it will eventually reach the required speed for take off.
    .
    .....
    MarkEagle
    .....<a href="http://discussion.treocentral.com/tcforum/index.php?s=">TreoCentral</a> | <a href="http://discussion.visorcentral.com/vcforum/index.php?s=">VisorCentral</a> Forum Moderator - Forum Guidelines
    .....Sprint PCS Treo 650
    .....God bless America, my home sweet home...
  8. #68  
    Quote Originally Posted by clulup View Post
    Here are two questions: do you think it is physically possible that an airplane rolls at 5 mph relative to the treadmill surface which rolls at 5 mph into the other direction?

    If yes, what is the speed of that airplane relative to the ground?
    Anytime you mention speed, always specify the reference frame (wrt = with respect to).

    Your questions:

    Stationary (wrt ground) treadmill surface; Plane rolling forward (wrt ground and treadmill) at 5 mph:

    Plane is moving at 5 mph relative to treadmill. Treadmill is moving at 5 mph relative to plane but in the opposite direction. Plane is moving at 5 mph wrt ground.

    The above illustrates the answer to your questions:
    Yes.
    5 mph.
    --
    Aloke
    Cingular GSM
    Software:Treo650-1.17-CNG
    Firmware:01.51 Hardware:A
  9. #69  
    Quote Originally Posted by ToolkiT View Post
    Thats the whole problem of this issue, the scenario in question cannot really happen or the wording is too confusing to give a precise answer.
    You can brake it down to some simple questions:

    In addition to the ones above (still waiting for answers), here's another one:

    Can a Ferrari driving on a treadmill moving backwards at the speed of the car relative to the ground reach 50 mph (relative to the ground)?

    Answer as discussed before: yes, it can, the wheels will be spinning at 100 mph, which is ok for a Ferrari. It would be like running at 4 mph on a treadmill running backwards at 2 mph. This proves that the whole issue has nothing to do with jets and propellers pushing back air. Also a car powerd by wheels could reach takeoff speed if it can drive fast enough. The whole plane thing is a red herring (apart from the wings of course).
    “Reality is that which, when you stop believing in it, doesn't go away.” (Philip K. ****)
  10. #70  
    Quote Originally Posted by MarkEagle View Post
    If the treadmill speed matches the speed that the plane would be moving down a runway, the plane is essentially standing still (as viewed by someone standing next to the treadmill)....
    Let's say the plane is moving forward (wrt ground) at 120 mph. The treadmill is stationary wrt ground.

    Now the treadmill starts it's motors and starts to move in the opposite direction at 120 mph (wrt ground). At this point, the plane is moving at 120 mph wrt an observer standing on the treadmill.

    For the plane to be stationary (wrt ground), the rearward force on the plane from rolling friction has to equal the thrust from the jet engines. That will NOT be the case if the pilots don't apply the brakes and the wheels are rolling.

    Ergo, the wheels will spin at twice the rate (ie at the rate it would if the plane were moving at 240 mph on the ground). But the plane will take off as it's ground speed will be 120 mph.
    --
    Aloke
    Cingular GSM
    Software:Treo650-1.17-CNG
    Firmware:01.51 Hardware:A
  11. #71  
    Clulup is right...... but only if the treadmill can exert enough force on the airframe to counteract the thrust of the jets (e.g. like in a stationary test of a jet).

    So, the real question is then, can the treadmill exert enough force on the airframe via the wheels (its only contact) to keep the plane stationary with respect to the air and the ground?

    If we accept that the force in question is due to friction, and that the wheels are designed to reduce that, and that friction does not increase with increased wheel speed (the only thing that the treadmill can influence, its only coupling to the plane) then the answer is that the treadmill can only exert a specific amount of force (thrust in the opposite direction to motion).

    The equation is:

    F=uR where u is the coefficient of friction and R is the force downward.

    As we can see its independent of the speed of movement. Therefore, no matter how fast the treadmill goes, due to friction in the ball-bearings, it can only exert a finite amount of force, say 500 newtons in to opposite direction of motion. The jet engine however can exert 60 000 newtons in the other direction, meaning the original problem is flawed, because there is no way, except for a very puny jet engine, for the force of fiction in the wheels of the engine to keep the plane stationary with respect to the ground.

    In fact the problem was obviously originally framed by some-one who did not understand that the force of friction was independent of the speed of movement (although stationary and moving co-efficient of friction are different).

    So in fact, Clulup is wrong.

    Surur
  12. #72  
    Quote Originally Posted by aprasad View Post
    Let's say the plane is moving forward (wrt ground) at 120 mph. The treadmill is stationary wrt ground.

    Now the treadmill starts it's motors and starts to move in the opposite direction at 120 mph (wrt ground). At this point, the plane is moving at 120 mph wrt an observer standing on the treadmill.

    For the plane to be stationary (wrt ground), the rearward force on the plane from rolling friction has to equal the thrust from the jet engines. That will NOT be the case if the pilots don't apply the brakes and the wheels are rolling.

    Ergo, the wheels will spin at twice the rate (ie at the rate it would if the plane were moving at 240 mph on the ground). But the plane will take off as it's ground speed will be 120 mph.
    From a physical point of view, there is nothing wrong with this. But that isn't the point. It is not how the problem works. If it says the treadmill is moving at the speed of the airplane relative to treadmill, the treadmill can never start moving from 0 mph when the plane is already at 120 mph.

    In a way, you could say that the power of logic prevents the airplane from taking off in the "treadmill matches speed of airplane relative to treadmill surface"-version, not the rolling friction. You can also say that this special case is not relevant or realistic in the real world (fair enough) but that doesn't change the conditions given in the problem (interpretation of the relative speed).
    Last edited by clulup; 12/12/2006 at 10:22 AM.
    “Reality is that which, when you stop believing in it, doesn't go away.” (Philip K. ****)
  13. #73  
    If fact, the wheels just confuse the issue.

    Lets replace the wheels with skids. This will only increase friction by removing the bearings and increasing the surface area generating friction. So we have a plane on skids on a treadmill going in the opposite direction.

    The jet engine on the plane just has to exert enough force bigger than F=uR to start accelerating. Once it is accelerating, if thrust is constant, it will continue to accelerate, as surface to surface friction is independent of speed. Eventually it will reach take of speed with respect to the ground, and take off.

    To appreciate it intuitively, have you ever used an orbital sander. You will appreciate that its not the speed of the sander that influences how difficult it is to control, but how hard it is pressing on the surface.

    Surur
  14.    #74  
    Quote Originally Posted by clulup View Post
    Just for the record: you say it is impossible that an airplane rolls at 5 mph relative to the surface of a treadmill that rolls at 5 mph in the opposite direction?
    I say that it's impossible for a treadmill to match the speed of an airplane (relative to the treadmill) if the airplane is moving relative to the ground.

    Quote Originally Posted by clulup View Post
    Most people in those discussions are sloppy about what "the conveyor belt matches the speed of the airplane" means. As mentioned many times now, if it means "conveyor belt matches the speed of the airplane relative to the ground/the air", the plane takes off.


    If it means "matches the speed of the plane relative to the conveyor belt",...
    It can't. If the laws of physics hold, then this interpretation requires a=a+b, where b>0.

    There's no point in debating an interpretation that requires suspending either the laws of physics or the principles of math.
  15.    #75  
    So does peeing into a bucket make you heavier?
  16. #76  
    I another one:

    You are on an airplane. Lunch is served. After everyone has eaten and the visited the restrooms etc, is the plane heavier, the same, or lighter than before lunch was served?
    --
    Aloke
    Cingular GSM
    Software:Treo650-1.17-CNG
    Firmware:01.51 Hardware:A
  17. #77  
    Quote Originally Posted by samkim View Post
    So does peeing into a bucket make you heavier?
    I'm not finding out ..
    --
    Aloke
    Cingular GSM
    Software:Treo650-1.17-CNG
    Firmware:01.51 Hardware:A
  18. #78  
    Quote Originally Posted by aprasad View Post
    You are on an airplane. Lunch is served. After everyone has eaten and the visited the restrooms etc, is the plane heavier, the same, or lighter than before lunch was served?
    I would say, in the case of an air- and water-tight transatlantic jet with more than 100 people on board, about 2.5 tons lighter than before lunch was served. Correct?
    “Reality is that which, when you stop believing in it, doesn't go away.” (Philip K. ****)
  19. #79  
    Let's see what others think.
    --
    Aloke
    Cingular GSM
    Software:Treo650-1.17-CNG
    Firmware:01.51 Hardware:A
  20. #80  
    Quote Originally Posted by samkim View Post
    So does peeing into a bucket make you heavier?
    I think: yes, while you are peeing (gravity acting on the pee stream).
    After you are finished, the weight returns back to normal.
    --
    Aloke
    Cingular GSM
    Software:Treo650-1.17-CNG
    Firmware:01.51 Hardware:A
Page 4 of 5 FirstFirst 12345 LastLast

Posting Permissions