# Wheels appear to go backwards? **URL:** \ **Category:** Factual Questions\ **Created:** [February 7, 2011, 12:05am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458 "2011-02-07T00:05:20Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![loshan](https://avatars.discourse-cdn.com/v4/letter/l/ce73a5/32.png) [@loshan](https://boards.straightdope.com/u/loshan)\ **Post date:** [February 7, 2011, 12:05am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/1 "2011-02-07T00:05:20Z")
What is the visual mechanism that makes wheels on a car appear to be turning backward while the car is moving forward? I notice this alot in commercials and have always wondered. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [February 7, 2011, 12:07am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/2 "2011-02-07T00:07:52Z")
Mismatch between wheel rpm and camera frame rate. The spokes are just short of being in the same position per frame. ---
**Author:** ![loshan](https://avatars.discourse-cdn.com/v4/letter/l/ce73a5/32.png) [@loshan](https://boards.straightdope.com/u/loshan)\ **Post date:** [February 7, 2011, 12:14am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/3 "2011-02-07T00:14:44Z")
Thank you. You have vastly improved my Super Bowl commercial viewing experience. ---
**Author:** ![Superfluous\_Parentheses](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@Superfluous\_Parentheses](https://boards.straightdope.com/u/Superfluous_Parentheses)\ **Post date:** [February 7, 2011, 12:26am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/4 "2011-02-07T00:26:00Z")
To expand a bit on **runner pat** ’s answer, video recording works by taking pictures at a certain rate (say, 50 pictures/second - it depends on the medium). The wheel on the car also rotate at a certain rate depending on the speed (say, 24 rotations/second). In this scenario, every time a picture is taken, the wheel has done slightly less than 1/2 of a full turn. If the wheel has 4 spokes, you can’t actually see the difference between slightly less than 1/2 turn or a slight rotation backwards. But your vision interprets it as a backwards rotation because the forward (correct) interpretation is much faster than what our brain is set up to easily deal with. Example with 2 spokes: ```auto picture number: 1 2 3 4 5 6 wheel "spokes": - / | \ - / ``` The above is what you’d see if the camera rate matches the rotation rate and the spoke was turning anti-clockwise, but it also matches what you’d see if the camera rate was 0.75 times the rotation of the spoke and it was rotation clockwise. This works for many close ratios and also depends on the symmetry of the “wheel” (basically, the number of “spokes”). ---
**Author:** ![Superfluous\_Parentheses](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@Superfluous\_Parentheses](https://boards.straightdope.com/u/Superfluous_Parentheses)\ **Post date:** [February 7, 2011, 12:32am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/5 "2011-02-07T00:32:41Z")
> [@Superfluous\_Parentheses](#): > > The above is what you’d see if the camera rate matches the rotation rate and the spoke was turning anti-clockwise… I meant to say here: if the camera rate **was 4 times** the rotation rate. ---
**Author:** ![loshan](https://avatars.discourse-cdn.com/v4/letter/l/ce73a5/32.png) [@loshan](https://boards.straightdope.com/u/loshan)\ **Post date:** [February 7, 2011, 12:53am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/6 "2011-02-07T00:53:07Z")
Thanks for the answers. I couldn’t decide if it was a film/video artifact or if they do this IRL. I never thought to look for it when driving. You know, the whole “look where you’re going” thing interferes with me looking at other’s wheels while on the road. 😉 ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [February 7, 2011, 12:55am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/7 "2011-02-07T00:55:27Z")
You won’t see it in real life, just on film/video. ---
**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\ **Post date:** [February 7, 2011, 12:59am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/8 "2011-02-07T00:59:14Z")
You can sometimes see it in real life, due to the microsaccades your eye performs while viewing a scene. Nevertheless, checking this while driving is contraindicated. ---
**Author:** ![twickster](https://avatars.discourse-cdn.com/v4/letter/t/ec9cab/32.png) [@twickster](https://boards.straightdope.com/u/twickster)\ **Post date:** [February 7, 2011, 1:04am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/9 "2011-02-07T01:04:29Z")
Thanks for asking, **loshan** , I’ve always wondered about this – but never wondered hard enough to ask. 😉 ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [February 7, 2011, 1:18am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/10 "2011-02-07T01:18:14Z")
nm ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [February 7, 2011, 1:22am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/11 "2011-02-07T01:22:14Z")
> [@runner pat](#): > > You won’t see it in real life, just on film/video. Just a nitpick…you will see it in real life if the wheel is illuminated by a strobe light, or a florescent fixture, which acts like a strobe light. And the strobe light acts like a motion picture camera shutter to produce the same effect. Admittedly, this isn’t going to happen outdoors on a sunny day. ---
**Author:** ![Mr\_Downtown](https://avatars.discourse-cdn.com/v4/letter/m/8e8cbc/32.png) [@Mr\_Downtown](https://boards.straightdope.com/u/Mr_Downtown)\ **Post date:** [February 7, 2011, 1:22am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/12 "2011-02-07T01:22:26Z")
[The master’s explanation.](http://www.straightdope.com/columns/read/730/how-come-the-wheels-of-a-moving-car-appear-to-rotate-backward-sometimes) ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [February 7, 2011, 1:22am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/13 "2011-02-07T01:22:38Z")
One can see the “wagon wheel effect” at night under certain streetlights. The lights look like they’re steady, but they’re really going off and on at 60 cycles per second due to the alternating current frequency. edit- Too slow! ---
**Author:** ![loshan](https://avatars.discourse-cdn.com/v4/letter/l/ce73a5/32.png) [@loshan](https://boards.straightdope.com/u/loshan)\ **Post date:** [February 7, 2011, 1:44am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/14 "2011-02-07T01:44:23Z")
> [@Mr\_Downtown](#): > > [The master’s explanation.](http://www.straightdope.com/columns/read/730/how-come-the-wheels-of-a-moving-car-appear-to-rotate-backward-sometimes) So I guess that makes me a wanker? Cool. I always thought having girly bits excluded me from wanker territory. And, no problem **twickster** , I’m glad to be of some use around here 😉 ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [February 7, 2011, 6:29am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/15 "2011-02-07T06:29:36Z")
This is an instance of a more general phenomenon known as [aliasing](https://secure.wikimedia.org/wikipedia/en/wiki/Aliasing). ---
**Author:** ![Hennessy](https://avatars.discourse-cdn.com/v4/letter/h/a9a28c/32.png) [@Hennessy](https://boards.straightdope.com/u/Hennessy)\ **Post date:** [February 7, 2011, 7:12am UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/16 "2011-02-07T07:12:35Z")
I have seen this a few times rolling down the highway, its one of those things you don’t want to quit watching as you just know its a once in a lifetime thing. I always thought it was a steady path and over a certain speed thing. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [February 7, 2011, 1:08pm UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/17 "2011-02-07T13:08:03Z")
> [@california\_jobcase](#): > > One can see the “wagon wheel effect” at night under certain streetlights. The lights look like they’re steady, but they’re really going off and on at 60 cycles per second due to the alternating current frequency. Nitpick: don’t you get a 120-Hz flicker, because the light illuminates when the current is moving in either direction? ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [February 7, 2011, 2:55pm UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/18 "2011-02-07T14:55:20Z")
I first noticed this as a kid when I saw _Chitty Chitty Bang Bang_. Very disorienting. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [February 7, 2011, 3:08pm UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/19 "2011-02-07T15:08:13Z")
Always fun: [![]( " - YouTube") ](https://www.youtube.com/watch?v=iXP8mwViK9o) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [February 7, 2011, 3:46pm UTC](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458/20 "2011-02-07T15:46:21Z")
> **[Wagon-wheel effect](https://en.wikipedia.org/wiki/Wagon-wheel_effect)** > > The wagon-wheel effect (alternatively called stagecoach-wheel effect) is an optical illusion in which a spoked wheel appears to rotate differently from its true rotation. The wheel can appear to rotate more slowly than the true rotation, it can appear stationary, or it can appear to rotate in the opposite direction from the true rotation (reverse rotation effect). > The wagon-wheel effect is most often seen in film or television depictions of stagecoaches or wagons in Western movies, although reco... [Next page](https://boards.straightdope.com/t/wheels-appear-to-go-backwards/570458.md?page=2)