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I Force to stop a person on a treadmill

  1. Mar 22, 2017 #1
    We are doing a study & our calculated force is MUCH higher than our data. I'm wondering if our calculation is right.
    how much force it would take to stop a person in a wheelchair (83kg) going 6km/hr and stopping in 10 cm or within 2 sec. as an example?

    This is my calculation..Am I on the right track? F= ma We can find a using v=at+v0 so a=v/t so (1.67)/(2) = .835 ( v0=0 which treadmill initial speed) So f= 83*.835= 69.35 N

    If you wanna find it at 10cm (.1m ) you can use conservation energy formula as well Fd = 1/2 mv 2 so mad=1/2mv2so a= v2/2d so in this case a=1.672/.1= 13.94 m/s so F = 8313.94=1157.39 N
     
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  3. Mar 22, 2017 #2

    russ_watters

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    The problem is that those are two very different requirements. Which one do you want?
     
  4. Mar 22, 2017 #3
    Why would you expect to have constant acceleration during the stopping event?
     
  5. Mar 22, 2017 #4
    the one with the stopping distance.
     
  6. Mar 22, 2017 #5

    russ_watters

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    The answer you calculated looks correct to me.
     
  7. Mar 22, 2017 #6

    russ_watters

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    ...by the way, the title of the thread is a bit confusing and implies an answer of zero. Could you clarify the setup?
     
  8. Mar 22, 2017 #7

    berkeman

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    And are they on a treadmill or in a wheelchair? Or both?
     
  9. Mar 22, 2017 #8
    They are on a wheelchair on a treadmill. The weight is weight of the participant + wheelchair
     
  10. Mar 22, 2017 #9

    berkeman

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    What stops? The wheelchair with respect to the moving treadmill surface? The treadmill surface and the wheelchair keeps rolling? Or some combination? These are kind of important details if we are to give you good help.

    Do you have a sketch of the setup?
     
  11. Mar 22, 2017 #10

    berkeman

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    Or (after re-reading your OP), is the person in the wheelchair moving with the treadmill initially with their wheelchair wheels not rotating?
     
  12. Mar 22, 2017 #11
    the participant in wheelchair is moving with the same speed as treadmill. Then they told him to stop ( and as a result participant went back with a wheelchair a certain distance)
     
  13. Mar 22, 2017 #12

    berkeman

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    Sorry if I'm being dense here, but the volunteer in the wheelchair shoots off the back of the treadmill when they stop rolling themselves forward? Could you give a full explanation of the experiment, and say what it is that you want to learn from the experiment?
     
  14. Mar 22, 2017 #13
    Sorry for being confusing. No I meant like brake line ( you try to stop the car by pushing the brake but you go a little distance before the car stops). Once we told the participant to stop, he went back a little trying to stop the chair before the chair fully stopped
     
  15. Mar 22, 2017 #14

    berkeman

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    So you turned off the treadmill motor at the same time the volunteer was told to stop? Do you have a video?
     
  16. Mar 22, 2017 #15
    No. But here is the paper that our student wrote regarding this study
     

    Attached Files:

  17. Mar 22, 2017 #16

    sophiecentaur

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    If this is a real, practical problem then why does the wheelchair user ever need to be travelling backwards on the belt? You can use a strap to prevent that happening and then you don't need to brake him her. But a treadmill is not a very suitable exercise machine for an arm propelled vehicle. It's specifically for leg exercise. When the runner is in the air, there is no force from the track but the chair wheels are being turned by the belt when the hands aren't pushing. I don't think it's an equivalent exercise to 'road work'. If you used a safety strap on a runner, it would topple her over but it's fail safe for a wheel chair. Hands off and wheels just go round on their own.
    My brain hurt, reading this and I am trying to picture what it's like to actually do this thing. If the wheels are not rotating, the chair is moving backwards on the belt (no?). I'm assuming that the chair is being propelled by the arms to stop it going backwards but, when the hands aren't on the wheels, they will be turning 'forward' but any bearing or rolling friction will be pulling the chair backwards. This is much harder than running on the mill.
    Edit: I just discovered the post with the paper. Lots of it! Great invention to have a servo assist, rather than a simple motor with a lever control. The treadmill tests are really difficult to grasp and I'll need to read them through and post again.
     
  18. Mar 22, 2017 #17

    berkeman

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    I only skimmed the paper so far, but id does indeed say that the treadmill is turned off when the volunteer is told to stop their chair. Without a video, and without a clear/short explanation of what the study was trying to figure out, it's hard to be of much help.
    IMO, the treadmill experiment does not help you answer this simple question. It introduces so many other effects. Work is distance * Force, and the Work done to stop is equivalent to the Kinetic Energy in the motion of the person & wheelchair right before they begin to stop. That is a pretty simple calculation (assuming constant stopping force, which was mentioned early on as a question).
     
  19. Mar 22, 2017 #18

    sophiecentaur

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    Absolutely. Doing it that way introduces more questions than it answers. What you could do is what they do in the UK MOT test for cars on a rolling road, But if you want to find the braking efficiency then why not use an accelerometer (included in most spare phones and Apps are available) with the chair being operated on a horizontal surface? You can measure the effect of extra drag from the drive roller this way too.
     
  20. Mar 22, 2017 #19
    Sorry guys by my job is just comparing the data with calculation not to change the study protocol. Can you please guide me how to calculate the force in this condition? Yes , 100% horizontal and no slope.
     
  21. Mar 22, 2017 #20

    A.T.

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    But the methodology seems flawed. A treadmill is only equivalent to movement over ground, when it runs at constant speed (equivalence of inertial frames). You cannot simulate over ground accelerations by changing the treadmill speed, because that doesn't require acceleration of the entire mass, just changing the rotation speed of the wheels.
    Seems like a waste of time. The forces you get form this are meaningless for actual over ground use.
     
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