Just caught this, Carl. Not debunked, just not a big effect.
It’s one side not the other because the wheels turn in opposite directions–one clockwise, the other counter clockwise–when the car moves. True from both your perspective and from that of the nuts. So RH thread tightens on one side, but loosens on the other.
Related to the “mirror paradox” BTW.
Got it. Thanks. Used imagination. Stood facing wheels on each side. Saw CW vs CCW.
Yeah, the mirror thing. Using my clipper to shear my whiskers. Motions work, sorta.
And the movie thing. Wheels seem to turn the opposite way from what one would expect?
Carl
Yes, I’ve noticed that as well, Carl. The backward motion appears even in commercials for the car, where it would not seem to help their image to the public.
What you see is the stroboscopic effect caused by the camera rapidly “sampling” the wheel at some frame rate (16-60 times per second depending on the particular film or video camera). Slow moving things move smoothly, while fast moving things can be blurred unless the exposure time per frame is sufficiently short.
But rotating things like wheels on a car or a harmonic balancer are different in another way. If the shutter (or illumination) is synced with the rotational motion, they appear stationary. But if the frame rate (or illumination rate) is not synced but close to being so, they can appear to rotate in either direction. If the exposure occurs a little ahead of schedule, you catch the wheel a bit earlier and it seems to have moved backwards. I’m sure you’ve noticed this when you glance at a (belt-driven) pulley other than the balancer while you’re timing an engine. It will appear to move slowly unless its diameter is identical to that of the balancer pulley.
But what I don’t understand is why car commercials, films of stage coaches, etc. usually seem to have the wheels moving slowly backwards. I would think that in some (half of?) cases they would seem to move slowly forward.
Wheels seem to turn the opposite way from what
one would expect?
I think the actual process involved is called “precession”. Basically, if you
have a round peg in a round hole that’s a bit loose, moving the peg around in
circles within the hole causes it to roll, and the rolling looks to be the
opposite direction of the circles you’re moving the peg in. The same effect
requires bicycle pedals to be left-hand thread on the left side, even though
you may think the left-hand threaded pedal should go on the RIGHT side
based on which direction each pedal is actually rotating relative to its shaft.
When it’s a single threaded attachment, such as a bicycle pedal, it’s pretty
clear how precession works. When it’s a set of 4 or 5 lug nuts, it’s never
struck me as clear that precession is a thing. I guess one could run an
experiment and install all the lug nuts on a car finger-tight and then drive
around a bit and see if the ones on the right side get tighter while the ones
on the left side loosen up even more.
– Kirbert
Thank you for more examples. Clarifies a bit more for me. But, also muddles a bit as well.
In the round peg in the slightly loose hole example, is it the material with the loose hole that is being rotated, and causes the peg to rotate within the hole. And could that peg actually be rotating in the opposite direction?
Shoot, were it not for the lousy weather out and the Super Bowl, I might just go out to the shop and create an example in wood. r perhaps even in metal!!!
Bicycle pedals:
Indeed, that beings back kid memories. My earliest use of tools involved taking bicycles apart. Mix and match done more than once. The latest was a full restoration of a derelict. new fenders, pedals, tires and tubes, matching wheels and new pedals!!!
Jeweled no less. Oh, grips and a basket of the bars.
No gears then, one speed. New Departure Coaster brake. Two little flaws, a break in ewither and voila, no brakes!!!
To the point. As the pedal spun on bearings around the shaft that had handed threads into the crank, it seems that no motion would be imparted that might allow the shaft to back out.
But, misuse often resulted in pedal disintegration
nd kid feet right on the shaft. Then, yes, unless very firmly seated, backing out seems inevitable.
Agree lug nuts in different rotational axis would act differently. Little, as Bob says, or not at all. Not to completely disagree with Bob, but, I tend to the latter.
But, for the exercise of grey matter alone, very meaningful discussion. Beats the h… outta that other …
Carl
I had the word right, precession, but apparently the term more commonly
refers to the movement of a tilted axis of a gyroscope or planet, so a Google
search didn’t work right. I eventually found the correct link. This should be
VERY helpful:
BTW, I think the knock-off caps on splined hubs always have left-hand
threads on the left side. Easy to keep straight because the ears on the
knock-off itself indicate which way you need to whack it to get it on and off.
Modern racing cars use a similar setup in which the wheel engages pins as it
is installed, and it’s held secure by a single big nut. Is that big nut left-hand
thread on the left side of the car? Anybody know? You can watch those
wheels being swapped on and off in pit stops in F1 and other racing venues,
but it all happens so fast I dunno if you can ever tell which way the air
wrench is spinning the nut.
– Kirbert
Can be either way. Depends on whether the knock-off to wheel centre engagement is designed with epicyclic or hypocyclic geometry. Jaguar versus Lotus Elan, for example.
Slick! But, should not the red circle be turning CW and have an arrow or means of depicting that motion to be more easily understood.
And, I wonder if that CW vs CCW on more conventional 5 lug wheels, ala NASCAR. Answering my own question. I think all nuts are the same. The nuts are affixed with cement so as to ease the installation. No left wheels vs right wheels.
Carl
Slick! But, should not the red circle be turning CW and have an arrow
or means of depicting that motion to be more easily understood.
The red circle is stationary. Clearly, it’s not as easily understood as I hoped.
– Kirbert
Got it. Thanks.
Spurred me to think some more.
A planetary gear system.
A stick and a ring. Poke the stick in the opening ,
Revolve the stick CW. In contact with the ring, motion should be imparted. Ring goes CW as well.
Carl