# Very Weird question about force(sort of) **URL:** \ **Category:** Factual Questions\ **Created:** [September 6, 2005, 2:42am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286 "2005-09-06T02:42:49Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![copperwindow](https://avatars.discourse-cdn.com/v4/letter/c/4af34b/32.png) [@copperwindow](https://boards.straightdope.com/u/copperwindow)\ **Post date:** [September 6, 2005, 2:42am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/1 "2005-09-06T02:42:49Z")
I have a really weird question. If I’m biking up a hill and I fart, will the fart propell me up at all, sort of how an airplane flies? ---
**Author:** ![Rhubarb](https://avatars.discourse-cdn.com/v4/letter/r/59ef9b/32.png) [@Rhubarb](https://boards.straightdope.com/u/Rhubarb)\ **Post date:** [September 6, 2005, 3:04am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/2 "2005-09-06T03:04:20Z")
Yes, if you fart in the right direction. Force is a vector, after all. You will be propelled through a simple application of F=mA, but since the m and A are quite small, so is the F. My physics professor once asked the class to imagine that they were stranded on a completely level, frictionless surface. How could we extricate ourselves from this situation? His answer was to suck air in in one direction, and blow it out in the other. But farting would work too. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [September 6, 2005, 3:20am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/3 "2005-09-06T03:20:57Z")
> [@Rhubarb](#): > > YHis answer was to suck air in in one direction, and blow it out in the other. But farting would work too. You assume those were two different answers. **copperwindow** , an airplane doesn’t fly by thrust, it does so by lift. Thrust is needed to get airspeed to generate lift but thrust alone won’t make you fly like a plane. A sufficiently powerful flatus will may help you to fly ballistically like a rocket. ---
**Author:** ![roger\_thornhill](https://avatars.discourse-cdn.com/v4/letter/r/d9b06d/32.png) [@roger\_thornhill](https://boards.straightdope.com/u/roger_thornhill)\ **Post date:** [September 6, 2005, 4:02am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/4 "2005-09-06T04:02:05Z")
Not sure about that, but could you just make sure you do all your testing and piloting somewhere remote? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [September 6, 2005, 4:18am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/5 "2005-09-06T04:18:00Z")
In theory, yes. In practice, you’d be hard-pressed to measure the effect, let alone feel it. You would get more boost if you ignited the fart, but still not a measurable amount. ---
**Author:** ![waterj2](https://avatars.discourse-cdn.com/v4/letter/w/858c86/32.png) [@waterj2](https://boards.straightdope.com/u/waterj2)\ **Post date:** [September 6, 2005, 4:26am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/6 "2005-09-06T04:26:00Z")
Well, every time _I_ suck in a full breath’s worth of air, I have to blow it out before I can get around to sucking in more air. Although, using your nose for one and your mouth for the other might help, as thrust via the nose is more in the vertical direction. ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [September 6, 2005, 4:29am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/7 "2005-09-06T04:29:10Z")
Merged two threads. **samclem** GQ moderator ---
**Author:** ![waterj2](https://avatars.discourse-cdn.com/v4/letter/w/858c86/32.png) [@waterj2](https://boards.straightdope.com/u/waterj2)\ **Post date:** [September 6, 2005, 5:27am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/8 "2005-09-06T05:27:38Z")
First, I’ll clarify that my last post was in response to **Padeye**. Second, I’ll add that strategic farting could help drop those drafting you, and thus help you ascend faster, due to not having to drag them up the hill with you. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [September 6, 2005, 7:24am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/9 "2005-09-06T07:24:38Z")
> [@Rhubarb](#): > > My physics professor once asked the class to imagine that they were stranded on a completely level, frictionless surface. How could we extricate ourselves from this situation? His answer was to suck air in in one direction, and blow it out in the other. But farting would work too. ‘Swimming’ in the air would be more effective. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [September 6, 2005, 9:11am UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/10 "2005-09-06T09:11:07Z")
> [@waterj2](#): > > First, I’ll clarify that my last post was in response to **Padeye**. Second, I’ll add that strategic farting could help drop those drafting you, and thus help you ascend faster, due to not having to drag them up the hill with you. I’m not aware that being drafted makes extra work. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [September 6, 2005, 4:49pm UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/11 "2005-09-06T16:49:13Z")
> [@Rhubarb](#): > > His answer was to suck air in in one direction, and blow it out in the other. But farting would work too. No need to change directions: Assume you and the air start with velocity = zero. Thus the combined linear momentum is zero. When you suck the air in, You move it from outside your face, into your lungs. Once your lungs are full, the air has zero velocity. Conservation of linear momentum is satisfied if you also end up with zero velocity. You will have only a slight translation forward, such that you and the air’s CG remain fixed. When you blow the air out, it retains a velocity, and thus momentum. Conservation of momentum requires that you are left with equal and opposite momentum…and thus velocity. And yes, farting would work. ---
**Author:** ![BobLibDem](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/boblibdem/32/3149_2.png) [@BobLibDem](https://boards.straightdope.com/u/BobLibDem)\ **Post date:** [September 6, 2005, 4:53pm UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/12 "2005-09-06T16:53:45Z")
Why would lit fart force \> unlit fart force? Wouldn’t both leave the body at the same speed and thus impart the same momentum? ---
**Author:** ![sciguy](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@sciguy](https://boards.straightdope.com/u/sciguy)\ **Post date:** [September 6, 2005, 5:35pm UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/13 "2005-09-06T17:35:15Z")
> [@BobLibDem](#): > > Why would lit fart force \> unlit fart force? Wouldn’t both leave the body at the same speed and thus impart the same momentum? Well, unless you’ve got a pilot light inside your rectum (rectum? Darn near killed 'em!), you’d get a (small) push twice from a lit fart. 1. From the fart leaving your body 2. Lighting the fart then causes the air around it to heat up, which causes it to expand, which causes the expanding air to push on your body, giving a small momentum transfer. The second boost won’t be much (even compared to the first) since at least half of the expansion doesn’t impart any push to your body. ---
**Author:** ![Finagle](https://avatars.discourse-cdn.com/v4/letter/f/b19c9b/32.png) [@Finagle](https://boards.straightdope.com/u/Finagle)\ **Post date:** [September 6, 2005, 6:36pm UTC](https://boards.straightdope.com/t/very-weird-question-about-force-sort-of/320286/14 "2005-09-06T18:36:48Z")
> [@BobLibDem](#): > > Why would lit fart force \> unlit fart force? It wouldn’t. But it would look cooler. The amount and pressure of gas are both small enough so that the difference in velocity would be hard to measure. You’d probably get more benefit (still imperceptible) out of the decrease in mass that you have to push up the hill.