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B Why people float inside free falling airplane

  1. Mar 6, 2016 #1
    in science shows , an airplane made to fall freely under gravity has its passenger floating in mid air
    i understand weightlessness is due to 0 normal reaction by floor on person
    but since both passenger and plane have same aceleration due to gravity
    what might be reason for relative separation bet floor and feet to increase.?
    is this due to diff in initial velocity before free fall?
     
  2. jcsd
  3. Mar 6, 2016 #2

    A.T.

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    Here you assume that the plane in the videos goes to exactly 1g downwards, and never slightly above.

    Why would there be a difference in initial velocity, if you just sit in your seat? However, once in free fall, even small forces will cause you to drift around. Elastic objects that were compressed by the normal force, would restitute and "jump up" from the surface.
     
  4. Mar 6, 2016 #3
    The plane has air resistance, while the person inside is isolated from air resistance. But then the plane also has an engine, so it can dive faster than free fall... making sense yet?
     
  5. Mar 8, 2016 #4

    Janus

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    Consider this: You have a spring standing upright on a surface. You compress it, and then suddenly release it. The spring suddenly decompresses and jumps a bit into the air. Now consider someone standing in a gravity field. Gravity is pulling down on him and slightly compresssing him, His muscles are exerting forces to keep his body from collapsing, etc. If you suddenly remove the gravity, the compression relaxes and the muscles are suddenly pushing against a downward force that is no longer there. The reaction is going to be the same as when you released the pressure on the spring. He will push away from the floor and drift.
     
  6. Mar 8, 2016 #5

    OCR

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    Lol, take a ride in the "vomit comet" ...[COLOR=#black]..[/COLOR]:oldruck:
     
    Last edited: Mar 8, 2016
  7. Mar 9, 2016 #6
    Also, the PIC (pilot in command), has a very sensitive G meter, prominently displayed in front of him , and has practiced this vomit comet maneuver, to perfection, least all the unharnessed occupants, be thrown to the rear bulkhead, to be bloodied and broken.
     
  8. Mar 9, 2016 #7

    CWatters

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    ..and any slight deviation from the ideal path causes...
    Try throwing two balls to friend at the same time. Can you keep them in contact for the whole flight path?
     
  9. Mar 9, 2016 #8
    i think ive got it
     
  10. Mar 9, 2016 #9

    HallsofIvy

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    Well, I guess you really have it!

    But, just because I have to stick my oar in, perhaps this is something that has not been addressed yet. Some people seem to think, perhaps because they always see pictures of people "floating" in the middle of the airplane, that there must be some force moving you away from the sides of the airplane. There aren't. You still have the acceleration due to gravity, downwards, but now the airplane has that same acceleration so is not pressing on you. But if, at the beginning of this "weightlessness", you were near the floor of the airplane, during it, you will stay near the floor.
     
  11. Mar 9, 2016 #10

    berkeman

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    I wonder if they still use the metal nut on a string... :biggrin:
     
  12. Mar 9, 2016 #11
    Not even close. Should you care to view, what a modern, not quite as sensitive, "recording G meter" looks like, you can go to the Aircraft Spruce and Specialty Company website, and get an idea. These units are FAA requirements for all prop driven aerobatic crafts, whether flow in airshows, or for private "yanking, and banking".. A number of modern crafts in this category, have wings of complex wooden structure, design stressed to 9 G's ( aircraft grade Stitka spruce, or and FAA approved substitute) w/ "rib stitched" modern, FAA approved, polyester fabric covering. If during a flight session or airshow display, the recording G meter shows at or above the structured limit, ALL wing inspection covers must be removed, and w/ a flashlight, and mirror, all the structural components, spars, spar attach points, ribs, rib attach points, rib stitching, wing bay wire bracing and attach points, etc., must be inspected, and an entry made in the airframe logbook. The craft can't be legally flow again, under FAA rules, until that entry is noted in the logbook, OR, the wings are rebuilt/ replaced, and the appropriate entry made in the logbook... Them's the FARS, and their written in someone's life's blood. At some airshows like Oshkosh, there's an FAA rep on site, to check recording G meters, after each session of practice, and display, or sometime before the next take off, where the rep will reset the meter. Pheeew, a bit long, but I thought you might care for a bit more depth. Bob
     
  13. Mar 9, 2016 #12

    berkeman

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    Interesting stuff, thanks.

    I just remember from about 35 years ago when my then-girlfriend was working with the monkeys that were going to fly on the Space Shuttle, she got to ride with them on the Vomit Comet. The investigators wanted to see how the monkeys would respond to being in zero-g. My girlfriend told me that they all laughed when the got on the plane and the pilots showed them what they used for their "meter" to track zero-g in the dives -- it was a metal nut suspended from the cockpit ceiling with a string. They said they just pushed into the dive until the string wasn't taut anymore, and kept the nut floating for the rest of the dive.

    BTW, just like people, about half of the monkeys got sick on the flight. :smile:
     
  14. Mar 10, 2016 #13
    Now, don't get me wrong, the nut might still be there to this day. Aviation has a long history of providing redundancies to crucial systems, especially when specific precision maneuvers are concerned, the nut, may be, and would be a realistic, back up, w/ the PIC watching the gauge, and the Co-pie watches the nut, and the gauge from an angle sitting right seat. If he should note any discrepancy, it time for the G meter, to head for the shop, for re-calibration
     
  15. Mar 10, 2016 #14

    A.T.

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    It's even more cruel to cats, when their righting reflex kicks in and they start spinning like crazy:

     
  16. Mar 10, 2016 #15

    berkeman

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    Ouch, brutal...
     
  17. Mar 13, 2016 #16
    They would get used to it eventually, typically, and stop trying to react? Or is it like getting dizzy when you spin, it always happens and you will get just as dizzy every time? Most of my cats have adapted not to use their claws when they are falling against a human, it hurt, we yell in pain, all but one will not dig their claws in except Penny just can't stop herself. Some start to use claws and then retract them, others will not use their claws at all and will slide to a controlled crash instead, but only when human injury would result, otherwise its "claws to the wall". I wonder if it is directly wired to their balance system... and they can't disallow their reaction.
     
  18. Mar 13, 2016 #17

    A.T.

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    Reflex usually means that it is involuntary. Not sure what exactly triggers it though.
     
  19. Mar 13, 2016 #18
    in vomit comet will it be possible to create art floating in air (the paint itself floats ) using spraying can etc
     
    Last edited: Mar 13, 2016
  20. Mar 13, 2016 #19
    I would think the spray drops would be more coherent in the lack of gravity and the spray would be more uniform and more consistently follow the inverse square law of diffusion... the "spray" is projecting the paint with velocity, in a linear manner rather than a group being perturbed by gravity. Think of how a sneeze travels in zero G straight across as far as the room goes, where in 1G there is a maximum distance your snot could travel before 1G brings it to Earth...
     
  21. Mar 13, 2016 #20
    suppose paint tubes are used for a thickened flow
    although it may be messy
     
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