rimey@ucbmiro.ARPA (Ken Rimey) (08/21/85)
> If the truck won't roll going around a corner on the flat ground > with the tilt meter indicating 25 degrees, does that mean if it > is stationary on the side of a hill with the guage reading 25 > degrees it won't roll? If not, is there any correlation at all > between the two? I seem to remember from physics classes in long > forgotten years that gravity and acceleration were indistinguishable, > but that was MANY years ago. > > -- Ken Bates Yes, it is a fundamental principle that acceleration and gravity are indistinguishable. It seems to me that the tilt reading at which two wheels will leave the ground is independent of whether you are turning or traversing a slope. On the other hand, I can think of a few differences that come into play once you are on two wheels. First, if you are turning a corner, you may be able to straighten the wheel before you actually flip. More interesting from a physics point of view is the observation that turning involves ROTATION as well as acceleration. The truck will behave to some degree like a gyroscope. This effect translates an outward tipping torque into additional weight on the front wheels. Perhaps other readers will care to estimate the importance of this effect. Ken Rimey rimey@berkeley
bet@ecsvax.UUCP (Bennett E. Todd III) (08/21/85)
In article <10041@ucbvax.ARPA> rimey@ucbmiro.UUCP (Ken rimey) writes: > ... >More interesting from a physics point of view is the observation that >turning involves ROTATION as well as acceleration. The truck will >behave to some degree like a gyroscope. This effect translates an >outward tipping torque into additional weight on the front wheels. On one hand I wouldn't expect gyroscopic effects to be sufficient to be noticible, since the rate of revolution is so slow. On the other hand, I have noticed when accelerating while cornering rapidly that my car leans to the outside and to the front -- the front outside wheel is really pressing down vigorously. Since this is only noticible while accelerating it doesn't seem obviously gyroscopic, but since acceleration normally tends to make the car shift to the back, rather than the front, it is curious. Anybody know more about the mechanics of this situation? -- "Hypocrisy is the vasoline of social intercourse." (Who said that?) Bennett Todd -- Duke Computation Center, Durham, NC 27706-7756; (919) 684-3695 ...{decvax,seismo,philabs,ihnp4,akgua}!mcnc!ecsvax!bet or dbtodd@tucc.BITNET
bet@ecsvax.UUCP (Bennett E. Todd III) (08/21/85)
Another thought about gyroscopic properties of this system -- the
gyroscopic behavior of the vehicle as a whole is probably insignificant
considering how slowly it is revolving, but the gyroscopic behavior of
the *wheels* is probably significant. My first guess would be that the
gyroscopic behavior of wheels would tend to stabilize the vehicle
against rolling, but I can't seem to visualize the vectors -- intro
physics was too long ago.
-Bennett
--
"Hypocrisy is the vasoline of social intercourse." (Who said that?)
Bennett Todd -- Duke Computation Center, Durham, NC 27706-7756; (919) 684-3695
...{decvax,seismo,philabs,ihnp4,akgua}!mcnc!ecsvax!bet or dbtodd@tucc.BITNETrubin@mtuxn.UUCP (M.RUBIN) (08/22/85)
If you are taking a corner at 25 degrees "tilt", you are probably going rather fast on a paved road. Large bumps are not to be expected, and if you see any ahead you can slow down. You will probably also skid before you roll (see below). On the other hand, bumps are fairly common on hillsides and slowing down doesn't help much. Psychologically, when taking a corner you can still *see* that you're on flat ground regardless of what your inner ear (or tiltmeter) says. The brain probably averages these readings somehow. Jeeps *are* infamous for capsizing in turns on the highway, because of the above illusion and because (unlike cars) they will roll before they will slip sideways appreciably. Wider modern 4WD's aren't as bad.
pmk@prometheus.UUCP (Paul M Koloc) (08/25/85)
> Psychologically, when taking a corner you can still *see* that you're > on flat ground regardless of what your inner ear (or tiltmeter) says. > The brain probably averages these readings somehow. > > Jeeps *are* infamous for capsizing in turns on the highway, because of the > above illusion and because (unlike cars) they will roll before they will slip > sideways appreciably. Wider modern 4WD's aren't as bad. In to these considerations is the almost instantaneous response of the brain to gauge the "rate of increase in force". If you are in a train entering a constant radius turn on a flat bed track so that no slipping will take place, the passenger car will "lurch" just as it enters the turn. The same effect would occur if you simulated a "slope" by putting your vehicle on a rigid deck and then tilting the deck about an axis under the mid-line of the vehicle. This effect is worse for high center of gravity machines. If the deck were tilted very slowly to a fixed roll, not much would happen, but if it were abrupt the vehicle would tend to continue tilting beyond the equilibrium point for the fixed roll inclination. Unless you have "taken" a hell of a lot of curves, the brain will sense the "jerk" or "roll" acceleration and then extrapolate it to the point in time where the vehicle should flip over. It takes the brain about a second to recalculate new information that the "roll jerk" has zeroed out. Experience teaches the brain to make "better estimates, and that's what gives racing drivers that extra edge. Be careful not to use your static hill side settings as safe values for similar settings in high speed turns because, like your kinetic senses and brain, that instrument has delayed response. In addition, the instrument can have inertial errors. - - NOTE: MAIL PATH MAY DIFFER FROM HEADER - - +-------------------------------------------------------+--------+ | Paul M. Koloc, President: (301) 445-1075 | FUSION | | Prometheus II Ltd., College Park, MD 20740-0222 | this | | ..umcp-cs!seismo!prometheus!pmk.UUCP | decade | +-------------------------------------------------------+--------+
carl@aoa.UUCP (Carl Witthoft) (08/27/85)
>Another thought about gyroscopic properties of this system -- the >gyroscopic behavior of the vehicle as a whole is probably insignificant >considering how slowly it is revolving, but the gyroscopic behavior of >the *wheels* is probably significant. My first guess would be that the >gyroscopic behavior of wheels would tend to stabilize the vehicle >against rolling, but I can't seem to visualize the vectors -- intro >physics was too long ago. > This and many other responses to the original question (tipping of the truck) seem to be trying too hard. The truck simply tips when there is a net force on any vector not parallel to the perpendicular to the truck's frame. WHether this is due to sitting on a hill, turning sharply, or turning while speeding up (these last two, by the way, both are best viewed in terms of angular momentum and torque--any change in the velocity VECTOR means there is acceleration),is irrelevant to the final effect. BTW, the torque generated by the wheels does make some difference. Go look at (e.g. Halliday&Resnick) pictures of a top precessing, and you'll see that a car will behave more stably turning to the left than to the right ( unless I got those switched again??). But why worry about tipping-- just use a trapeze harness (<==))). Darwin's Dad (Carl Witthoft) ...!{decvax,linus,ima,ihnp4}!bbncca!aoa!carl @ Adaptive Optics Assoc., 54 Cambridgepark Dr. Cambridge, MA 02140 617-864-0201 "Put me in, Coach. I'm ready to play today. Look at me! I can be centerfield."
dbmk1@stc.UUCP (Derek Bergin) (08/29/85)
In article <290@ecsvax.UUCP> bet@ecsvax.UUCP (Bennett E. Todd III) writes: > >On the other hand, I >have noticed when accelerating while cornering rapidly that my car >leans to the outside and to the front -- the front outside wheel is >really pressing down vigorously. Since this is only noticible while >accelerating it doesn't seem obviously gyroscopic, but since >acceleration normally tends to make the car shift to the back, rather >than the front, it is curious. Anybody know more about the mechanics of >this situation? >-- > From the viewpoint of a non-physicist (and no I don't know why I'm submitting articles to this newsgroup) -- Depending on the type of vehicle (ie whether it's designed for cornering at high speed - unlikely in a country with a 55 mph speed limit :-) ) there is a certain cornering speed built into the suspension calculations when a car is designed. As cornering involves a braking force in the original direction of travel the front will tend to "dip" into the corner ie in the original direction. At normal (read design) speeds this will not be noticable - this is known as giving the customer a comfortable ride, however if you are applying more forward force then you will increase this dip until the tyres cease to hold the road. At this point the front corner comes up quite noticably as you sit back and enjoy the accident ( and yes this *is* based on personal experience ). A normal European "sportscar" type would not exhibit much body roll below speeds of approx 80 mph and probably much more - from the little I've seen of American Jeep type vehicles I would have thought that the problem became apparent at considerably lower speeds. Regards Derek !seismo!mcvax!ukc!stc!dbmk1 I used to think I was expressing an opinion - but there again people used to think the world was flat.
throopw@rtp47.UUCP (Wayne Throop) (08/29/85)
> Go look at (e.g. Halliday&Resnick) pictures of > a top precessing, and you'll see that a car will behave more stably turning > to the left than to the right ( unless I got those switched again??). > Darwin's Dad (Carl Witthoft) > ...!{decvax,linus,ima,ihnp4}!bbncca!aoa!carl OK. I went and looked at my Haliday&Resnick picture of a top precessing. I'm still not enlightened. In what way will this effect cause a car to be more stable turning left than right? -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw
carl@aoa.UUCP (Carl Witthoft) (09/04/85)
In article <163@rtp47.UUCP> throopw@rtp47.UUCP (Wayne Throop) writes: >OK. I went and looked at my Haliday&Resnick picture of a top >precessing. I'm still not enlightened. In what way will this effect >cause a car to be more stable turning left than right? x The wheels themselves have an angular momentum vector which points to the left (when the car is moving forward). Now, when you turn the car left or right, these angular momentumvectors precess just like the top. There is a restoring force to match this effect. I'm far to fogyheaded to remember which way the precession and force go, but you can check it out bysitting on a bar stool (the rotating kind), holding a bicycle wheel, spinning it up, then rotating the wheel on its axis. The stool (and you) will start to turn. Anyway, the point is that the car's turn in one direction or the other will cause the wheels' precession to be such that the restorig force will act against the overall centrifugal "force" which is trying to tip you over. Hope this helps. Darwin's Dad (Carl Witthoft) ...!{decvax,linus,ima,ihnp4}!bbncca!aoa!carl @ Adaptive Optics Assoc., 54 Cambridgepark Dr. Cambridge, MA 02140 617-864-0201 " Buffet-Crampon R-13 , VanDoren B-45, and VanDoren Fortes ."
throopw@rtp47.UUCP (Wayne Throop) (09/08/85)
Well, I'm still looking for enlightenment with regard to momentum-nature (:-). The story so far: > > > [Original posting asserting there is a non-symmetric effect in a > > > spinning wheel when turned left vs. when turned right, and > > > instructions to meditate on the picture of a precessing top in > > > Halliday & Resnick to be enlightened as to the nature of this > > > non-symmetric effect.] > > OK. I went and looked at my Haliday&Resnick picture of a top > > precessing. I'm still not enlightened. In what way will this effect > > cause a car to be more stable turning left than right? > I'm far to fogyheaded to remember which way the precession and force go, > but you can check it out bysitting on a bar stool (the rotating kind), > holding a bicycle wheel, spinning it up, then rotating the wheel on its > axis. OK. I went and got a barstool and a spinning bicycle tire. (Don't you just love obeying strange directions gotten from a computer?) I'm still not enlightened. The effects I could discover are completely symmetric with respect to left and right. Unless somebody comes up with a *much* more convincing koan (:-), I'm still assuming that there is *no such (asymmetric) effect*. -- Truth in advertising leads me to comment that I didn't get a barstool and a tire, but I *did* get a gyroscope and a rig to put it in, and observed the effects. These are the same effects mentioned in Halliday & Resnick, and are, as mentioned above, completely symmetric with respect to left and right. In case it is interesting, in both directions of turn there was *more* tipping force due to gyroscopic effects. In particular, the spinning tire has a momentum vector pointing left. A left turn introduces a vector pointing up. The gyroscopic effects create a vector pointing forward. In a right turn, the introduced vector points down, and the gyroscopic vector points back. All neatly symmetric. Carrying it further to the precessional rotations results in the same symmetry (since any precessional rotations reverse direction with a reverse in turn direction). Is there some non-symmetric effect I'm missing? I can comment from my experiments that if the effect exists, it is *very* small compared with the gyroscopic effects I observed. (And all you net.zen.buddists out there don't need to beat me over the head with a stick and shout "MU", either! :-) -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw