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I What are the aspects that can help a car to flip in a turn?

  1. Sep 7, 2016 #1
    I am not sure if this is the right place to ask it, but this is a question that I thought today, and it gave me some curiosity to understand. Imagine that a car will curve, we can say the turn is a bit tight , what are the factors that can help it to flip? I was wondering about some aspects:

    1. if the car has mass, it has inertia, so while it is curving it tends to keep the motion in the same direction that it was instants before the turn. right? So, if the car has more mass, it has more inertia, and since there is friction, one heavier car would flip easier then one lighter, considering that all other possible variables were equal.

    2. Center of gravity, a car with an higher center of gravity would flip easier. The whole inertia of the car distributed to higher heights would be further of the tires(where friction acts), creating angular momentum.

    3. The car being thin because it has less surface contact with the ground;

    4. The car being lighter. This opposes what I've said in "a)", but a heavier car is more difficult to get off the road. A lighter car has more instability.
    Am I wrong? In what I'm wrong? What do you think?

    Thanks for helping. :)
  2. jcsd
  3. Sep 7, 2016 #2

    Simon Bridge

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    You can work these out by using a free body diagram ... to turn the sum of forces must add to a horizontal resultant poiting towards the center of the turn. Friction is applied at the wheels, but the center of mass is is in a different place so the car will naturally try to rotate (torque between road and com). This is countered by vertical reaction forces at each side of the car. Look up "tipping force".

    If the friction between car and road is too small, the car will slide.
    If the friction is high, but the center of mass is too high, then the car will roll.
    (Also consider if the camber is wrong...)

    To actually flip a car requires hitting something in the road or detonating an explosive under the chassis - this is what is usually done in movies.
  4. Sep 7, 2016 #3


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    1. I don't think that's necessarily true. The car with more mass has more downward force and probably bigger tires as well, hence more friction. All things being equal I think mass is a wash.

    2. Yes, higher center of gravity for sure.

    3. Perhaps more importantly, the lever arm is shorter, i.e., the center of gravity is at a higher angle above the support points (the tires).

    4. See #1.

    All of these things aside, it's actually pretty hard for a car to just flip based on its own tire friction.. Most cars just can't generate that kind of sideways force. Instead, the tires would just slip. Most likely you'd have to leave the pavement and/or get snagged on a step in the road surface or something like that to actually flip by accident. (There were a few SUVs some years ago which were actually tippy enough to go unstable during emergency maneuvers.)
  5. Sep 7, 2016 #4

    Simon Bridge

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    High com cars can be quite easy to turn over ... but the com has to be high compared with the width of the wheelbase.
    Richard Hammond managed to tip his van in Top Gear's "man with a van" challenge, and Clarkson famously rolled a robin reliant - but it turns out that was faked.

    Formula 1 cars may slide or spin out, but they only actually flip in collisions - these can be spectacular due to the aerodynamics.
    A Bond film managed to flip an austin martin DBS (Casino Royale remake?) by using an explosive ... I think they claimed some sort of record for most number of rolls onscreen in a single stunt. this was after deliberately trying a flip using a ramp iirc.

    All these can be found on youtube ... don't you love the internet age??!
  6. Sep 8, 2016 #5
    In the 1977 move _The Car_ starring James Brolin-


    had a really cool sequence towards the end of the movie where 'The Car' (a self willed and indestructible car that was the villain of the movie) winds up tumbling side over side and takes out two intercepting police cars. Was one of the most amazing 'tumbling car' sequences I have seen in a movie. I don't think I have seen the Bond roll sequence, but based on total ignorance and the itchyness of my index finger, I might suggest that this sequence might be a fair challenger to the Bond film. It is an amazingly cheesy and campy movie, but I always found it fun (seen it on TV at least 2 or 3 times... somehow) and great for its quantity and quality of totally over the top automobile stunts.

    Actor, Director and stuntman Hal Needham ( http://www.imdb.com/name/nm0624102/?ref_=fn_al_nm_1 ) was also a virtuoso of staging some of the most far out (even preposterous) car rolling, flying and tumbling car stunts..... which would often involve explosions as well, and almost invariably would conclude with a 'relief shot' of the driver crawling out of the wreck.

    The television car chase, with the attendant tumbles, crashes, rolls and other 'auto-batics' seem to be fading from the scene. Back when I was a kid (in the 1970's) they were a staple of television, in a few cases, that was the major content of the show. From Rockford Files to Dukes of Hazzard.

    I guess now all we really have is NASCAR, and those damn restrictor plates have really reduced the frequency of cars going airborne at Talledega and Daytona. We did however get to see the heroic Juan Pablo Montoya vanquish the evil Jet Dryer at Daytona in 2012.

    Last edited: Sep 8, 2016
  7. Sep 8, 2016 #6


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    That effect is proportional to mass, just like the opposite inertia effect in 1), so they cancel. Similar for static friction (approximately).

    Not sure what you mean here. A less dense car is more likely to be fliped over by stong winds (e.g. empty trailer truck ). But for flipping in curves it is mainly vertical CoM position v.s. axle width.
  8. Sep 9, 2016 #7


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  9. Sep 9, 2016 #8


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    Not sure why bigger tyres will create more friction? It should be independent of surface area.
  10. Sep 9, 2016 #9

    Simon Bridge

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