Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Loop-the-loop normal force

  1. Mar 19, 2005 #1
    Can anyone provide an explanation as to what the normal force is reacting to in the case when a jet is flying a loop-the-loop?? I understand for a rollercoaster that at the top of the loop the normal force is due to the track exerting a force back on to the rollercoaster cart, contributing to the centripetal force, but for a plane, where is the normal coming from???

    Only thing I can imagine is that it has something to do with the inertia of the plane?? But then why would the normal act downwards at the top of the loop?

    Cheers
     
  2. jcsd
  3. Mar 19, 2005 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The air.

    AM
     
  4. Mar 19, 2005 #3

    Doc Al

    User Avatar

    Staff: Mentor

    On the plane itself, consider the vertical forces acting at the top of the loop: The air pushing on the plane ("lift") and gravity. These forces must produce the (downward) centripetal acceleration of the plane if the plane executes circular motion.

    The term "normal" force is usually reserved for the perpendicular force between two surfaces, such as between car and track in the roller coaster case. In the airplane example, one could ask for the normal force on the pilot (exerted by the plane) at the top of the loop.
     
  5. Mar 19, 2005 #4
    look at it, as whats exerting the normal force on the person in the plane, which would be the chair.
     
  6. Mar 19, 2005 #5
    Normal force

    For the plane moving in a circle. If the magnitude of the velocity is constant, then by Newton's second law, the net force on the plane is towards the centre (centripetal force). The pilot in the plane (if tightly secured to the seat) will also move in a circle. At the top of the loop the weight acting on the pilot and force exerted by the seat on the pilot act downward. These two forces provide the size of the centripetal force.

    n +mg = mv*v / r rearranging for n gives n = m(v*v /r - g)
     
  7. Mar 19, 2005 #6

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    And what is it that provides the force on the seat that the pilot feels. It can't be gravity. It is the force of the plane against the air.

    AM
     
  8. Mar 19, 2005 #7
    so if the track exerts a force on a car in loop to loop, what exerts the force on the track?
     
  9. Mar 20, 2005 #8

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The mass/inertia of the rest of the rollercoaster and the earth to which it is attached.

    AM
     
  10. Mar 21, 2005 #9

    The forces are the aerodynamic forces of lift which (usually) point up from
    the wings. When the plane is upside down, the wings point down.

    The easy way to visualize this is that there is a vaccum condition just above
    the wings of plane which always pull the wings toward the vacuum.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Loop-the-loop normal force
Loading...