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Tipping a truck

  1. Mar 25, 2004 #1
    Is a truck easier to tip over in a crosswind if it is travelling at a high speed, or lower speed?

    As far as I can tell, it makes no difference. But this doesn't seem logical.

    If anyone knows where a similar problem has been worked out, I would love to see it.
     
  2. jcsd
  3. Mar 25, 2004 #2
    Probably depends upn the angle of the truck, to the wind, inasmuch as it probably works out a little like sailing a boat...and they will sail into the wind, or pretty close to directly into it...it's a lead/clue...
     
  4. Mar 25, 2004 #3
    Assume a perpendicular wind.

    I don't think the sailboat analogy works, because here we are only concerned with the truck tipping over.
     
  5. Mar 25, 2004 #4

    NateTG

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    In practice the difference is probably negligible, but I would guess that the truck is more difficult to tip at a higher speed.

    There are two different ways that the truck can react to cross wind: It can either slip, or it can tip. Increasing the forward speed of the truck makes it more likely to slip.

    Consider, for example a crosswind that is sufficient to tip a stationary truck. Now, if the truck is going forward so fast that the tires barely hold to the ground. Then, when the crosswind hits, the truck will slip to the side instead of tipping.
     
  6. Mar 25, 2004 #5
    OK, but the sailboat has relevance in the real world, but it works nicely here to do it simply...answers are (usually) easier to find...

    Also the speed of the truck would be very relevant to the Sailboat example, inasmuch as, it becomes a combination of the wind effects, that topples the truck...as the manner of the trucks generation of wind plays into its "tip'ablity"....and, is it a semi? or attached?
    (one piece truck)
     
  7. Mar 25, 2004 #6
    But don't you find it counterintuitive that the forward speed has no effect on tipping?
     
  8. Mar 25, 2004 #7
    I don't think the sailboat analogy works because, if anything, the sailboat is a more complicated system. Why substitute a relatively easy system for a complicated one?

    Rather than a truck, consider a sheet of stiff plastic attached to four tiny wheels so that the plastic extends vertically. Now, is it easier to blow the plastic over if it is standing still, or when it is moving? Assume a perpendicular wind.
     
  9. Mar 25, 2004 #8

    Njorl

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    A moving truck has angular momentum stored in the tires. Tipping would have to overcome this. This makes it that much harder to tip the moving truck. The engine and drivetrain also store angular momentum, but that vector would not rotate upon tipping, so it does not enter into the problem.

    You can treat the situation as if the truck is stationary. Change the wind to a diagonal one, such that the horizontal component is equal to the true wind velocity. I don't see this as making the truck more likely to tip though.

    There are practical, non-ideal concerns too. The moving truck is likely to encounter transient effects, like a bump. The energy supplied by that bump might be just the difference between tipping and not tipping. This may nt be important to a physics student, but it is probably important to a trucker.

    Njorl
     
  10. Mar 25, 2004 #9
    There is no such thing as a wind that blows in one direction for more thana few seconds, but, assuming that however the truck moves, the wind remains perpendicular, we have a case...

    The work performed by the truck against the wind is

    Displacement * Force = Mag(dis)Mag(For)cos(theta)

    Theta is the angle between the two vectors. Since the truck is perpendicular, theta is zero and the work is zero.

    Therefore, the truck is not having to fight the wind. Moving, it doesn't have to put forth any work to maintain its course.

    So the velocity of the truck is of no direct relevance.


    Yet, it is of an indirect relevance.
    Just because the wind is always perpendicular length-wise does not mean that it has also to be perpendicular height-wise.
    If the angle of the wind, height-wise, varies, the truck could be "tipped".
    The forces that would prevent this "tipping" are gravity and the friction of the tires.

    As the velocity of the truck increases, the friction of the tires to the ground will lesson, and "tipping" will grow likelier.
     
    Last edited: Mar 25, 2004
  11. Mar 25, 2004 #10
    RE: "A moving truck has angular momentum stored in the tires. Tipping would have to overcome this. "

    Which is why my plastic-sheet-mobile has tiny tires.


    Ignoring the tires, can we then say for sure that the speed of the vehicle has no effect on its stabilty in a crosswind?

    I don't see how a vertical bump affects the problem.
     
  12. Mar 25, 2004 #11

    Njorl

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    If the truck were on the verge of tipping onto the passenger side, and the bump was only on the driver's side, the truck would tip.

    Njorl
     
  13. Mar 25, 2004 #12
    Ignoring acceleration's and angular momentum's respective effects on the friction of the tires, there is NO relationship, JohnDubya.

    I do not think it is helpful for us to consider the bump, which is an upward force, scenario. It only complicates things.
     
  14. Mar 25, 2004 #13
    RE: "There is no such thing as a wind that blows in one direction for more thana few seconds,"

    You obviously haven't lived on the West Coast. :)

    RE: "The work performed by the truck against the wind is Displacement * Force = Mag(dis)Mag(For)cos(theta). Theta is the angle between the two vectors. Since the truck is perpendicular, theta is zero and the work is zero."

    Your argument applies to the net work, not the work done by the truck. An airplane can take a perpendicular path into a crosswind, but it does work on the wind because the propellors have to apply a force non-perpendicular to the wind. So does the truck.
     
  15. Mar 25, 2004 #14
    Never driven a truck either, clearly, the truck itself generates wind vectors and velocities that correspond to it's motion relative to the wind, you could easily be generating a vacuum pressure on the other side of the truck because it is moving forward, that might just help tip it real fast...so is it a constant windspeed, and again on a semi, or straight body truck?
     
  16. Mar 25, 2004 #15
    Let's assume a single truck, (say), a UPS truck.

    I don't see how the velocity of the truck would create a relative vacuum on one side of the truck as opposed to the other.
     
  17. Mar 26, 2004 #16
    Yup, OK, Uhmm, I have driven lots of trucks, the wind flows around the truck in an alternating manner, windspeed shifting higher/lower, changng from side to side, Heck drove a salt truck, dropped salt onto the road, so I could easily see the wind patterns behind the truck as the salt followed it, it makes like an S pattern behind it as it shifts from one side, high speed, to the other side, high speed....

    When driving, it is around 55 MPH that the air (molecules in the atmosphere) stops being 'split apart' (no, not 'atomically' split) and the vehicule starts pushing air in front of it...this too, would make a difference....

    Anyone want to test this out?
     
  18. Mar 26, 2004 #17
    How about taking a box and pulling it horizontally under water?
     
  19. Mar 26, 2004 #18
    Well sounds really good but relevant to the reality of the, well "real world" it would teach us much less, brute forces of physics rule in absolute conditions hence stationary will tip first, in Non-real scenario of "absolutism of condition"...but I suspect, in the real world, the moving truck would tip first, dependant upon conditions...more likely to be subjected to more 'opportunities' then the stationary one....

    Have Fun!
     
  20. Mar 27, 2004 #19
    Also it seems that every time I attempt to introduce what would be the "distinguishing factors" between a truck, moving, and not, you attempt to eliminate them as having consequence...which amounts to limiting/constraining the example to the point that it will no longer be a relevant question! soooo......
     
  21. Mar 27, 2004 #20
    JohnDubYa,

    I have to agree with Mr. Robin Parsons in the preivous post. You're making your question such a frequently moving target, it's too frustrating to try to answer it. You started with a truck, then it became a sheet of plastic with tiny wheels, then it turned back into truck (UPS). What next, a rocket engine on the roof pointing sidewise that comes on evertime the truck stops? :wink:

    How about restating your question based on all the changes you've decided to make since your first post, and then agree not to change it again for awhile.
     
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