# Car on a treadmill **URL:** \ **Category:** Factual Questions\ **Created:** [September 6, 2008, 8:39pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384 "2008-09-06T20:39:50Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [September 7, 2008, 5:17pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/61 "2008-09-07T17:17:41Z")
> [@Rick](#): > > My bad not #28 I restated **Chronos** ’s solution in post #47. Damn lack of coffee in the AM. > :smack: But again **Zhing** was correct, he/she didn’t say you we’re “wrong”, it was close but not the same as the OP in that he/she was interested in a situation where the treadmill dynamically matches the speed of the car relative to the ground/observer. In the situation you devised in #47 you’ve set the treadmill at 1 speed and then accelerated the car. The end result is the same when the car reaches 30mph (wrt ground), but arriving at that end result might have been part of the issue for **Zhing** in a situation where the conveyor dynamically matches the car’s speed (both wrt ground). ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [September 7, 2008, 5:19pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/62 "2008-09-07T17:19:57Z")
> [@ZenBeam](#): > > There’s a communication problem in this thread, and it’s not because of **Zhing**. The problem is that **Jman** , **Johnny L.A.** , **Rick** , **usedtobe** , **Jragon** , **Cosmic Relief** and possibly others are bringing their preconceptions of what **Zhing** is asking to the thread. The preconception is that they assume **Zhing** is referring to the speed of the car relative to the surface of the treadmill. He clarified way back in post 13 that he is talking about the speed of the car relative to the ground. Well, that’s your opinion. All he says in post 13 is “the car moves forward relative the ground”, which doesn’t clarify much of anything. We can guess what he meant only by virtue of the fact that he agreed with Chronos’s answer, which is no better than anyone’s except that by a flip of a coin he happened to be the one to choose the frame of reference that matched the one in the OP’s head. ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 7, 2008, 6:04pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/63 "2008-09-07T18:04:37Z")
> [@Cosmic Relief](#): > > Well, that’s your opinion. All he says in post 13 is “the car moves forward relative the ground”, which doesn’t clarify much of anything. Well, I think it clarifies a lot, but that’s not all I said in that post, I went on to say: > [@](#): > > If the plane doesn’t move (relative to the ground), the conveyor doesn’t move either. > > So, let’s consider such a conveyor belt with a car. It’s specially made to move in the opposite direction of the car (relative to the bystanders on the ground) with perfect accuracy and instantly. You step hard on the gas. What happens? > [@Cosmic Relief](#): > > We can guess what he meant only by virtue of the fact that he agreed with Chronos’s answer Can you describe what other scenario is possible and fits what I described that would have a different answer than the one Chronos gave? ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 7, 2008, 6:10pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/64 "2008-09-07T18:10:44Z")
> [@Cosmic Relief](#): > > All he says in post 13 is “the car moves forward relative the ground”, which doesn’t clarify much of anything. 😕 **Zhing** ’s response in post 13 certainly clarifies his OP. In the OP, **Zhing** asks: _“A car is standing on a runway that can move (some sort of band conveyer). The car moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the car’s speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the car move?”_ I asked if “The car moves in one direction” means relative to the treadmill surface, or relative to the ground?, and he answers “relative to the ground”. So we now have the question _“A car is standing on a runway that can move (some sort of band conveyer). The car moves in one direction relative to the ground, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the car’s speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the car move?”_ What’s unclear about that? How do you reasonably interpret it any way other than what I described in post 36? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 7, 2008, 6:19pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/65 "2008-09-07T18:19:22Z")
[![]( " - YouTube") ](https://www.youtube.com/watch?v=AShBoF1FPSE) ---
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [September 7, 2008, 7:02pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/66 "2008-09-07T19:02:16Z")
> [@ZenBeam](#): > > There’s a communication problem in this thread, and it’s not because of **Zhing**. The problem is that **Jman** , **Johnny L.A.** , **Rick** , **usedtobe** , **Jragon** , **Cosmic Relief** and possibly others are bringing their preconceptions of what **Zhing** is asking to the thread. The preconception is that they assume **Zhing** is referring to the speed of the car relative to the surface of the treadmill. He clarified way back in post 13 that he is talking about the speed of the car relative to the ground. > > With so many people making the same wrong assumption, it’s not surprising that **Zhing** is a little exasperated. I WAS talking about relative to the ground, I’m assuming the “sensor” is an outside observer. The treadmill doesn’t move unless it sees the car moving relative to the ground, which it won’t if the treadmill is exactly compensating. So it moves, our outside observer witnesses the car moving, the treadmill stops it, moving the exact opposite speed of the car (which, as the treadmill wasn’t moving, is the same on the ground and the treadmill). Of course, now the car ISN’T moving to any outside observer, it’s staying stationary even though on the treadmill itself it is effectively moving. Therefore our outside observer turns off the treadmill because the car is moving 0MPH to him. The car then moves and the outside observer… ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 7, 2008, 7:05pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/67 "2008-09-07T19:05:49Z")
Johnny L.A., Your first post in this thread was post #19. By that time I had clarified my question. Regardless, you posted this: > [@](#): > > I’m not sure why you’re having trouble. Here is a video of a motorcycle on a dynamometer. Clearly, the motorcycle does not move forward. The roller, which as has been said is sort of a ‘very short treadmill’ does indeed move – as it would have to. I responded by telling you “The conveyor I’ve described does not work in the same manner as a dynamometer”, and I quoted myself explaining why. I explain the following to Jman: > [@](#): > > No, the misunderstanding is with you. I clarified “relative to the ground” and “(relative to the bystanders on the ground)” . > > If the car is stationary to the outside observer, the treadmill is also. You then post: > [@](#): > > Is this a whoosh? Of course the treadmill as a whole is stationary on the ground. That’s the point of having a treadmill, so you can move forward over a surface without having to move forward in space. The treadmill as a whole is stationary. The track on the treadmill moves backward in relation to the ground. I explain to you again: > [@](#): > > Not a whoosh, I meant he belt itself. I wanted to know what would happen if you stepped on the gas in a car resting on a treadmill and the treadmill was set up in a way so the car and the belt moved at the same speed but opposite directions to an outside observer. My scenario should be crystal clear by now. However, you go on to post this: > [@](#): > > Your ‘clarifications’ make no sense. Let’s get to basics. I’m going to ask one question at a time. > > Do you agree that a treadmill is a certain machine that has a track that moves? I post back: > [@](#): > > Please, I’ve had enough of this. Yes, the track moves. Somehow I haven’t made myself clear to you. You go on to post this: > [@](#): > > I don’t mean to be insulting. But what you have said is that if the car is not moving, then the belt isn’t either. You don’t seem to accept what other people are saying, so I’m just trying to break it down. Let me quote you: Yes, I did say if the car isn’t moving the belt isn’t either. So? That’s accurate. You claim I’m not accepting what others are saying, but by this time I explain multiple times that I’m satisfied with Chronos’ description of what happens. Did you at any time tell me that he’s incorrect and I should be accepting an alternate explanation from others? No. You go on: > [@](#): > > So getting back to your quote, ‘If the car is stationary to an outside observer,’ the track is moving backward relative to the car. > > And this can be seen in **Duckster** ’s link. To you, the outside observer, the little R/C truck is stationary in space. Yet the treadmill track is clearly moving. Now it’s clear that you still don’t understand that in my scenario, the treadmill is designed that so that the track and car are still to an outside observer, or are both moving in opposite directions at equal speed relative to an observer. I explained multiple times that if the car/R/C truck is stationary to an outside observer, the track is also, so how you go on to post the above is a mystery to me. Even though I explained this multiple times and even directly to you. Finally, when explained to you again, you reiterate what Chronos explained, **which I accepted and made clear that I considered my question asked and answered** , and finish with “Where’s the problem?”, as if I still have a problem. Failure to Communicate? Absolutely. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 7, 2008, 7:27pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/68 "2008-09-07T19:27:57Z")
Jeez, dude! Calm down! My last post was meant to be a joke! Yes, I misconstrued your question. But you’re acting as if I’m the only one who did. Since I’m not, then that indicates that perhaps you share some of the blame. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 7, 2008, 7:44pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/69 "2008-09-07T19:44:20Z")
> [@Jragon](#): > > I WAS talking about relative to the ground, I’m assuming the “sensor” is an outside observer. From your post 51: > [@Jragon](#): > > 1.Car floors it, moves a little bit forward at (say) 60MPH > 2. Treadmill reacts, goes 60MPH the other way > 3. Car is not moving (even if wheels are), therefore the treadmill “compensates” by slowing to 0MPH again > 4. Car goes 60MPH again > 5. See 2 > 6. See 3. I interpreted this as you saying the car was traveling 60 Mph relative to the treadmill, but I see now I misunderstood. mea culpa. I don’t think that’s a good description of what would happen, however. The car can’t jump instantaneously to 60 Mph, it would accelerate continuously to that speed _relative to the treadmill surface_, while the treadmill surface accelerates backwards to -30 Mph. So to an observer on the ground, the car accelerates to 30 Mph. ---
**Author:** ![Jragon](https://avatars.discourse-cdn.com/v4/letter/j/e19b73/32.png) [@Jragon](https://boards.straightdope.com/u/Jragon)\ **Post date:** [September 7, 2008, 7:50pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/70 "2008-09-07T19:50:19Z")
> [@ZenBeam](#): > > From your post 51: > I interpreted this as you saying the car was traveling 60 Mph relative to the treadmill, but I see now I misunderstood. mea culpa. > > I don’t think that’s a good description of what would happen, however. The car can’t jump instantaneously to 60 Mph, it would accelerate continuously to that speed _relative to the treadmill surface_, while the treadmill surface accelerates backwards to -30 Mph. So to an observer on the ground, the car accelerates to 30 Mph. Oh! I see what you’re saying now, for some reason I was having trouble visualizing that, but it actually makes more sense than mine (FWIW I was taking acceleration into account but I forgot that the acceleration of the treadmill affected the total speed of the car). ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 7, 2008, 7:52pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/71 "2008-09-07T19:52:29Z")
> [@Johnny\_L.A](#): > > Jeez, dude! Calm down! I was perfectly calm in my above post, even by L.A. standards, dude. What indicates that I’m anything other than calm and need decaf? > [@Johnny\_L.A](#): > > My last post was meant to be a joke! Right. > [@Johnny\_L.A](#): > > Yes, I misconstrued your question. But you’re acting as if I’m the only one who did. No, I’m not acting that way. > [@Johnny\_L.A](#): > > Since I’m not, then that indicates that perhaps you share some of the blame. That’s possible. It’s also possible that after all the further clarification I gave you, I have little to no blame in your failure to comprehend my question, regardless of others not understanding my scenario earlier on. The reader can decide that for himself based on the run-down I gave in my previous post. I’m done here. Off to grab a large Burundi Kayanza. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 7, 2008, 8:36pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/72 "2008-09-07T20:36:31Z")
> [@Zhing](#): > > I was perfectly calm in my above post, even by L.A. standards, dude. What indicates that I’m anything other than calm and need decaf? Well, the time you put into it indicates a certain obsessiveness. [QUOTE=Zhing] Right. [/quote] You’re saying it wasn’t? Why else would anyone post a clip of _Cool Hand Luke_ except as a joke? [QUOTE=Zhing] No, I’m not acting that way. [/quote] You’re certainly paying more attention to me than to the half-dozen other posters who misinterpreted your posts. [QUOTE=Zhing] That’s possible. It’s also possible that after all the further clarification I gave you, I have little to no blame in your failure to comprehend my question, regardless of others not understanding my scenario earlier on. The reader can decide that for himself based on the run-down I gave in my previous post. [/quote] Oh, you poor victim! ‘It isn’t my fault! Nobody understands me!’ Let’s go over it. > [@Zhing](#): > > What would happen if a car were put on a treadmill **duplicating** the scenario from the plane on a treadmill problem: Emphasis mine. Right here, you’re setting it up as a **duplicate** of the airplane scenario. So you’ve planted a preconception in me and others. > [@Zhing](#): > > Remember, the conveyor matches the speed of the car, not its wheels. Here you’ve clarified. I admit that I missed it, since I was thinking about a duplicate of the airplane question. Obviously, others did as well. In the OP you also said: > [@Zhing](#): > > “A car is standing on a runway that can move (some sort of band conveyer). The car moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the car’s speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the car move?” Here you’re asking if the car can move. But then you say: > [@Zhing](#): > > The premise is “The car moves in one direction, while the conveyor moves in the opposite direction”. So you’re asking if the car can move, and then you specify that the car moves. **ZenBeam** says: > [@ZenBeam](#): > > Just like the plane version, you aren’t clearly stating the problem. Does the car move in one direction relative to the treadmill surface, or relative to the ground? To which **Chronos** gives you the answer, which is just an elementary algebra equation: x = v \* 2. It should have ended there. But there are more misunderstandings as people talk about a car remaining motionless to an outside observer. You say: > [@Zhing](#): > > The conveyor I’ve described does not work in the same manner as a dynamometer. But you don’t say why. **Telemark** asks you to clarify. You reply to Q.E.D.\*\*'s question: > [@Zhing](#): > > Read what I was replying to. It’s an example of a car with wheels on rollers where the car can’t move forward, but the rollers can spin. What is? The dynamometer example? Or the conveyor in your OP? What is ‘it’? **Q.E.D.** says the question was poorly written, after which you get all defensive. Then you reply to **Telemark** : [quote=Zhing] I already wrote that I agree with Chronos’ conclusion.\*\* Fine. But **Telemark** and others, myself included, think you’re still talking about a car that is stationary to an outside observer. Your answer does nothing to dispel that misconception. And so on, and so on. And then when I see what you’re getting at you become sarcastic. Excuse me, but do you really blame anyone for being incredulous when someone, in effect, asks ‘What’s thirty plus thirty?’? So you set up the question as being a duplicate of the airplane question, only with a car. You specify that the car moves forward. You specify that the car can’t move forward. When people say that you are not making yourself clear, you say ‘Yes I am! Read what I posted!’ when it’s clear that what you posted is being misunderstood by several people. It’s like the stereotypical Ugly American who thinks he can make himself understood in a foreign country by talking louder. If more than a few people are not understanding what you’re saying, you should rephrase it; not repeat it in the same way and then play the victim. ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [September 7, 2008, 9:46pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/73 "2008-09-07T21:46:11Z")
In the typical “plane on a conveyor” question, the speed of the conveyor is always matched to the speed of what the plane would be going at if it was doing the same thing _if it wasn’t on a conveyor_. That is, you have a plane putting out enough thrust to move forward at 30mph on normal ground, and a conveyor spinning backwards at 30mph. In the analogous situation with a car, it will remain stationary. Definitely. (That’s what treadmills are for!) This is not the situation that the OP is asking for, perhaps because he’s taking a poorly phrased question about planes that nobody worried about the phrasing of because they knew what it what it was _really_ asking. This is the cause of the confusion and miscommunication. The OP is asking what will happen if you have a car that is hooked to a treadmill that will always go exactly _half_ the speed the car would go on normal ground (that is, the speed of the wheels). So, if the car is accelerated until its speedometer says 20mph, the treadmill will roll backwards at 10mph, reducing the car’s apparent speed to observers to 10mph. If the car is further accelerated until its speedometer says 50mph, the treadmill will roll backwards at 25mph, reducing the car’s apparent speed to observers to 25mph. The answer to his question is that the car would drive off the front of the treadmill. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [September 7, 2008, 10:10pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/74 "2008-09-07T22:10:00Z")
> [@Jragon](#): > > I WAS talking about relative to the ground, I’m assuming the “sensor” is an outside observer. The treadmill doesn’t move unless it sees the car moving relative to the ground, which it won’t if the treadmill is exactly compensating. So it moves, our outside observer witnesses the car moving, the treadmill stops it, moving the exact opposite speed of the car (which, as the treadmill wasn’t moving, is the same on the ground and the treadmill). Of course, now the car ISN’T moving to any outside observer, it’s staying stationary even though on the treadmill itself it is effectively moving. Therefore our outside observer turns off the treadmill because the car is moving 0MPH to him. The car then moves and the outside observer… Well, then the car creeps forward at a rate determined by the efficiency of the observer’s responses. If the response is instant, the car doesn’t move relative to the observer (more accurately, it moves, but an arbitrarily small amount). Since perfect efficiency is impossible, the car’s front wheels will eventually slip off the treadmill and (assuming it’s a front-wheel drive), lurch forward, crash, and kill everyone within. ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 7, 2008, 10:17pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/75 "2008-09-07T22:17:00Z")
> [@Johnny\_L.A](#): > > Well, the time you put into it indicates a certain obsessiveness. Pot calling the kettle black? What’s that have to do with me calming down? Don’t you need to calm down by the same standards? All of my posts directed at you were in response to yours. I guess **I** need to calm down. > [@Johnny\_L.A](#): > > You’re saying it wasn’t? Why else would anyone post a clip of _Cool Hand Luke_ except as a joke? Since you’re asking for my opinion I’ll give it to you. It was to affirm in the mind of others that it’s me, not you, having problems with communication and to further a little mini pile-on. When it finally sank in what I asked, did I get a “sorry dude, I misunderstood”? No, there was no admittance of any fault of your own and you went on to give the answer that I accepted from Chronos long ago along with a superior attitude giving a condensing, “What’s the problem?”, as if I had one after accepting the correct answer from Chronos. Had you not had ego issues with the record in this thread of your inability to understand, I doubt you would have felt the need to post a video which was clearly an attempt to accuse me of showing more problems with communication than yourself. > [@Johnny\_L.A](#): > > You’re certainly paying more attention to me than to the half-dozen other posters who misinterpreted your posts. Oh you poor victim! Why is Zhing picking on me? > [@Johnny\_L.A](#): > > Emphasis mine. Right here, you’re setting it up as a **duplicate** of the airplane scenario. So you’ve planted a preconception in me and others. So fucking what? That the OP could have been explained better is irrelevant after all the further clarification given, much of it directly in response to your posts. > [@Johnny\_L.A](#): > > Here you’ve clarified. I admit that I missed it, since I was thinking about a duplicate of the airplane question. Obviously, others did as well. Many more times than that you missed clarifications, even when given by others. I can list them all for you if you like. > [@Johnny\_L.A](#): > > **Q.E.D.** says the question was poorly written, after which you get all defensive. No I didn’t “get all defensive”. Not in the least. > [@Johnny\_L.A](#): > > Fine. But **Telemark** and others, myself included, think you’re still talking about a car that is stationary to an outside observer. Your answer does nothing to dispel that misconception. Really? Here are a few of the posts up until that point where I cleared up the the misconception: “Sorry- relative to the ground.” “No, if the car is still in relation to the rest of us, the belt stays still also.” Here are others after that point that still didn’t get through to you: “If the car is stationary to the outside observer, the treadmill is also.” “Not a whoosh, I meant the belt itself. I wanted to know what would happen if you stepped on the gas in a car resting on a treadmill and the treadmill was set up in a way so the car and the belt moved at the same speed but opposite directions to an outside observer.” Now that last quote is clear as fucking day. And what do you write next? “Do you agree that a treadmill is a certain machine that has a track that moves?” Where the fuck did that come from? Your comprehension inability is still my fault apparently. You quote me saying “If the car is stationary to the outside observer, the treadmill is also.” Your response: _So the track moves._ What the fuck! It gets better. You go on (bolding mine): _Now let’s say someone uses the treadmill for its intended purpose. He is walking forward on the track. The means of locomotion makes no difference. He can be walking, or riding a bicycle, or driving a car. He is moving forward in relation to the track. The track is moving backward in relation to the person on it. **To the outside observer the subject is stationary in space and the treadmill track is moving backward.** _ Really? How many times has it been explained to you at this point that if the car is stationary to the outside observer, the track must be also? A lot! But I still must share some blame in your comprehension inability, right? Then you misquote me: _So getting back to your quote, ‘If the car is stationary to an outside observer,’ the track is moving backward relative to the car._ Where the fuck did I say that? How many times at this point did I explain the opposite? A lot! > [@Johnny\_L.A](#): > > If more than a few people are not understanding what you’re saying, you should rephrase it I did rephrase it! So did Jman and ZenBeam and that still didn’t help. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [September 7, 2008, 10:17pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/76 "2008-09-07T22:17:27Z")
> [@Bryan Ekers](#): > > Well, then the car creeps forward at a rate determined by the efficiency of the observer’s responses. If the response is instant, the car doesn’t move relative to the observer (more accurately, it moves, but an arbitrarily small amount). Since perfect efficiency is impossible, the car’s front wheels will eventually slip off the treadmill and (assuming it’s a front-wheel drive), lurch forward, crash, and kill everyone within. Well, then the car creeps forward at a rate determined by the efficiency of the observer’s responses. If the response is instant, the car doesn’t move relative to the observer (more accurately, it moves, but an arbitrarily small amount). Ultimately, the car should on average remain still. If the driver cranks it up to 60 and the observer has a slight response lag, the car moves forward relative to the ground. If the car brakes back to zero, and the observer has the same lag, the treadmill will move the car backward. As long as the car doesn’t change speed so much faster than the observer’s reflexes that it drives off the front of the treadmill or lets itself get tossed off the back of the treadmill, all is well. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [September 7, 2008, 10:19pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/77 "2008-09-07T22:19:01Z")
Christ in crotchless panties! I give up. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [September 7, 2008, 10:25pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/78 "2008-09-07T22:25:52Z")
> [@Zhing](#): > > Really? How many times has it been explained to you at this point that if the car is stationary to the outside observer, the track must be also? A lot! I have to admit, I don’t see how this is true. The car is stationary, but its wheels (and the axles and transmission and attached components) are in motion. The treadmill is stationary, but its track (and rollers and transmission and attached components) are in motion. Would it make any difference if the treadmill’s speed was changing and it was the job of the car’s driver to use the gas and brake pedals to keep the car still? ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [September 7, 2008, 10:31pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/79 "2008-09-07T22:31:07Z")
> [@Bryan\_Ekers](#): > > I have to admit, I don’t see how this is true. The car is stationary, but its wheels (and the axles and transmission and attached components) are in motion. The treadmill is stationary, but its track (and rollers and transmission and attached components) are in motion. > > Would it make any difference if the treadmill’s speed was changing and it was the job of the car’s driver to use the gas and brake pedals to keep the car still? He’s matching the treadmill to the speed of the car-relative-to-observers, not to the wheels-relative-to-ground/treadmill. As I said a little bit ago, to do this practically, you’d have the treadmill rigged to go backwards at half the speed reported by the car’s speedometer. This really has nothing to do with the airplane question. ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 7, 2008, 10:47pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/80 "2008-09-07T22:47:19Z")
> [@Bryan\_Ekers](#): > > I have to admit, I don’t see how this is true. The car is stationary, but its wheels (and the axles and transmission and attached components) are in motion. No. If the car is stationary, the wheels can’t be in motion. The treadmill in my example won’t allow the car to be still and the wheels be in motion at the same time because in that case the treadmill will be moving. > [@](#): > > if the car is still in relation to the rest of us, the belt stays still also. > [@](#): > > I wanted to know what would happen if you stepped on the gas in a car resting on a treadmill and the treadmill was set up in a way so the car and the belt moved at the same speed but opposite directions to an outside observer By ZenBeam: > [@](#): > > The treadmill is set up so that when the car is moving in one direction at a certain speed with respect to ground, the top surface of the treadmill is moving in the other direction at the same speed, also with respect to ground. For some reason during arguing with someone else that claimed a plane on a treadmill couldn’t take off, I couldn’t picture in my head what would happen on a treadmill that works as I described. Chronos clarified it for me. It seemed obvious right after reading it, but for some reason I couldn’t picture it. I’ll attribute it to staying up late and arguing on the internet. 😉 Here was Chronos’ explanation: > [@](#): > > In that case, the car’s wheels are spinning twice as fast as normal. So the car’s speedometer reads 120, the car’s going 60 one way (relative to the ground), and the belt’s going 60 the other way. [Previous page](https://boards.straightdope.com/t/car-on-a-treadmill/462384.md?page=3) [Next page](https://boards.straightdope.com/t/car-on-a-treadmill/462384.md?page=5)