# 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:** 1
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 6, 2008, 8:39pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/1 "2008-09-06T20:39:50Z")
What would happen if a car were put on a treadmill duplicating the scenario from the plane on a treadmill problem: _“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?”_ Remember, the conveyor matches the speed of the car, not its wheels. I can’t picture what would happen. 😕 ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 6, 2008, 9:20pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/2 "2008-09-06T21:20:19Z")
Since the speed of the conveyor belt directly effects the car, it could easily be made to keep the car motionless in relation to the rest of the world. The key point with a plane is that the wheels of the plane don’t provide any forward movement. A car’s wheels do. ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 6, 2008, 9:29pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/3 "2008-09-06T21:29:16Z")
> [@Telemark](#): > > Since the speed of the conveyor belt directly effects the car, it could easily be made to keep the car motionless in relation to the rest of the world. I’m not following you. You step on the gas hard enough so that the car would go 50 mph on the road. What happens? ---
**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 6, 2008, 9:31pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/4 "2008-09-06T21:31:28Z")
> [@Zhing](#): > > What would happen if a car were put on a treadmill duplicating the scenario from the plane on a treadmill problem: > > _“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?”_ Such a system already exists. You see them often in emissions testing stations. It’s called a “set of rollers” and the magic control mechanism is called “friction”. And no, the car never moves, not when the system is operating correctly. ---
**Author:** ![The\_Scrivener](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@The\_Scrivener](https://boards.straightdope.com/u/The_Scrivener)\ **Post date:** [September 6, 2008, 9:36pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/5 "2008-09-06T21:36:24Z")
No way this car takes off… on Mythbusters. They did the plane; no way they’ll do a mere car after that. Although they did revisit “JATO” [the jet-assisted take-off car] in a way… ---
**Author:** ![ChrisBooth12](https://avatars.discourse-cdn.com/v4/letter/c/e95f7d/32.png) [@ChrisBooth12](https://boards.straightdope.com/u/ChrisBooth12)\ **Post date:** [September 6, 2008, 9:38pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/6 "2008-09-06T21:38:06Z")
um arent these already used to check like torque or something? where they put a car on a bunch of rollers ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 6, 2008, 9:42pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/7 "2008-09-06T21:42:22Z")
> [@Cosmic Relief](#): > > Such a system already exists. You see them often in emissions testing stations. It’s called a “set of rollers” and the magic control mechanism is called “friction”. And no, the car never moves, not when the system is operating correctly. If the car doesn’t move, the rollers can’t either. The premise is “The car moves in one direction, while the conveyor moves in the opposite direction”. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 6, 2008, 9:49pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/8 "2008-09-06T21:49:13Z")
> [@Zhing](#): > > If the car doesn’t move, the rollers can’t either. The premise is “The car moves in one direction, while the conveyor moves in the opposite direction”. A roller is just a special case of a conveyor belt. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 6, 2008, 9:50pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/9 "2008-09-06T21:50:27Z")
> [@Zhing](#): > > The premise is "The car moves in one direction 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? ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 6, 2008, 9:51pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/10 "2008-09-06T21:51:05Z")
> [@Q.E.D](#): > > A roller is just a special case of a conveyor belt. I understand that. But if the car doesn’t move forward, the rollers can’t spin. Let’s keep it to a conveyor belt for simplicity’s sake. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 6, 2008, 9:52pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/11 "2008-09-06T21:52:57Z")
> [@Zhing](#): > > But if the car doesn’t move forward, the rollers can’t spin. This is not true. ---
**Author:** ![appleciders](https://avatars.discourse-cdn.com/v4/letter/a/85f322/32.png) [@appleciders](https://boards.straightdope.com/u/appleciders)\ **Post date:** [September 6, 2008, 9:54pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/12 "2008-09-06T21:54:04Z")
A car on a treadmill is basically the same problem as a person on a treadmill; both get motive force by pushing back against the conveyor belt. And we all know what happens when you walk on a treadmill. ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 6, 2008, 9:56pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/13 "2008-09-06T21:56:07Z")
> [@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? Sorry- relative to the ground. I’m assuming that’s what the plane on a treadmill problem was describing also. At least that’s the way it’s worded. “A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction.” 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? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 6, 2008, 10:02pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/14 "2008-09-06T22:02:13Z")
> [@](#): > > If the car doesn’t move, the rollers can’t either. The premise is “The car moves in one direction, while the conveyor moves in the opposite direction”. 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. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [September 6, 2008, 10:03pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/15 "2008-09-06T22:03:59Z")
> [@Zhing](#): > > 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? By the definition you just gave, the wheels spin, the belt compensates, and the car remains stationary with respect to the rest of the world. What is hard about this? And it is exactly the same as putting the car on a [roller-type dynometer](http://www.chassisdyno.net/). Just think of the roller as a very small conveyor belt. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [September 6, 2008, 10:04pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/16 "2008-09-06T22:04:04Z")
> [@ZenBeam](#): > > > [@Zhing](#): > > > > But if the car doesn’t move forward, the rollers can’t spin. > > This is not true. [Here’s a picture of a car on rollers](http://www.fordcaprilaser.co.uk/setting_up.htm) (third from the top), and a description of driving on them (the paragraph left of the picture). > [@Zhing](#): > > Sorry- relative to the ground. Well, that’s easy then. If the car is moving (say) ten Mph East, then the treadmill is moving ten Mph West. The car’s speedometer will read 20 Mph. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 6, 2008, 10:06pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/17 "2008-09-06T22:06:23Z")
> [@ZenBeam](#): > > [Here’s a picture of a car on rollers](http://www.fordcaprilaser.co.uk/setting_up.htm) (third from the top), and a description of driving on them (the paragraph left of the picture). That’s not at all equivalent to the situation posited in the OP: the front wheels are completely constrained. The car’s not going anywhere even if the roller seize up at full power. ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 6, 2008, 10:30pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/18 "2008-09-06T22:30:50Z")
> [@commasense](#): > > By the definition you just gave, the wheels spin, the belt compensates, and the car remains stationary with respect to the rest of the world. What is hard about this? No, if the car is still in relation to the rest of us, the belt stays still also. Okay, Chronos’ explanation makes sense to me. I don’t know why I was having such a hard time envisioning what would happen. ---
**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 6, 2008, 10:38pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/19 "2008-09-06T22:38:37Z")
> [@Zhing](#): > > No, if the car is still in relation to the rest of us, the belt stays still also. > > Okay, Chronos’ explanation makes sense to me. I don’t know why I was having such a hard time envisioning what would happen. I’m not sure why you’re having trouble. Here is a [video of a motorcycle on a dynamometer](http://www.youtube.com/watch?v=Tq4f_mjiyWQ). 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. ---
**Author:** ![Zhing](https://avatars.discourse-cdn.com/v4/letter/z/9d8465/32.png) [@Zhing](https://boards.straightdope.com/u/Zhing)\ **Post date:** [September 6, 2008, 11:00pm UTC](https://boards.straightdope.com/t/car-on-a-treadmill/462384/20 "2008-09-06T23:00:04Z")
> [@Johnny\_L.A](#): > > I’m not sure why you’re having trouble. Here is a [video of a motorcycle on a dynamometer](http://www.youtube.com/watch?v=Tq4f_mjiyWQ). 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. > [@](#): > > Remember, the conveyor matches the speed of the car, not its wheels. The conveyor I’ve described does not work in the same manner as a dynamometer. [Next page](https://boards.straightdope.com/t/car-on-a-treadmill/462384.md?page=2)