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Considered by many smokers to be something that cannot be done, it is nonetheless possible to ash one's cigarette or cigar out of the rear window of a car moving at high speed, provided one knows the proper technique.

This maneuver has always been troubling for two reasons: For one, passengers in the back seat do not have access to the leading edge of their window, they do not have the ability to simply ash out of a convenient slot and directly into the oncoming airstream, which carries the ashes along the body of and away from the vehicle*. The second problem is that the high speed of the wind passing the car tends to push the ash (and potentially some of the more dangerous embers) back into the car.

Traditionally, such unfortunate individuals were forced to take one of three solutions, each of which has its distinct drawbacks:

  1. Ash out of the driver's window
  2. Ash one of the internal ashtrays
  3. Ash into a cup or other receptacle

Ashing out of the driver's window is a bit tricky in that it forces you to reach foreward and over the driver's head. I suppose I needn't remind you that, doing this in a jumpy automobile at speeds at or above 60mph (96.5kph) with an incendiary device burning between 1112-1292°F (580-700°C)** is a very bad idea.

It would seem, then, that ashing into one of the internal ashtrays would be the best solution, but oftentimes the owner of the car does not wish to clean out his backseat ashtrays of all of your ashes (especially if he or she is a non-smoker). As well, using the internal ashtrays tends to fill the car with the odor of cigarette smoke and impart that odor to the interior. Further, some people are quite sensitive to cigarette smoke, so internal ashtray ashing is not a good idea.

Ashing into a cup or other receptacle (commonly a drink can) solves the problem of cleaning up after the mess (you can simply throw the can away), but is still bad for all of the reasons above, plus the added problem of being non-fixed in the affore-mentioned bumpy automobile environment. There's also the danger that someone might not know that the nearby coke can is your new ashtry, and attempt to take a healthy swig of it. This, also, is ungood.

What is a backseat smoker to do? Fear not, I'll talk you through it.


In order to understand how this works, we first need to understand a little about how the air enters and leaves a vehicle when one window is open. (Note: I'm not sure if this applies when more than one window is open, but it has worked for me in both situations).

 /                                                          (incoming air) /
<@@@@@@@@@@@@@@@@@@@                                        @@@@@@@@@@@@@@<@@@@
 \                 %@                                      @%              \
##################  %@                                    @% ###################
##################   %@@                                @%%  ###################
##################   %  @@                             @%    ###################
                      %   @@@@@@@@               @@@@@@@%       ^
                       %         @@@@@@@@@@@@@@@@@     %        |
                        %                              %        | Body of car
                        %                             %
			 %			     %
			 %			    %
			  %			    %
			  %			   %
			   %			   %
			    %%			   %
			     %%%	         %%
				%%%          %%%%
				   %%%%%%%%%%

The above diagram is a rough and exxagerated approximation of airflow through the local vicinity of one open window where (@) represents one possible airflow through the car and (%) represents another. (think of them as minimum and maximum ranges). The actual situation is much more complicated and involves eddies, and fluid dynamics, but the basic idea is this: when air enters the car, air must also leave the car. Air enters the car from the direction of travel (hopefully foreward) on the right. The speed at which the air is travelling, forces the air into the car. Because there are no other exits, air must also leave through this portal. The majority of the air leaves the car very soon after it enters it (airflow @). Some of it sticks around for awhile (airflow %). The trick to getting this to work is to find that spot where most of the air is leaving, and allow it to carry something with it; namely, the ash from your cigarette or cigar.

*******************************************
* CAR                                     *
*    _____________________________________*
*   /                                     *
*  /                                      *
* /     __________________________________*
*/     /    ^                             *
*     /   ideal spot                      *
*    /                                    *
*   /                                     *
*  /            WINDOW                    *
* /                                       *
*/                                        *
*******************************************
             The Playing Field

This spot is usually located towards the rear of the window as illustrated above. Once you have located it (a little tentative trial-and-error with paper will suffice), take your object of smoking and slowly slide it up the window, parallel to the surface of the window. Once it reaches this point, it should be sucked out, and if it is not, a little tap will suffice. Do not flick it as you would on an ashtray, as this will more than likely cause the ash to fall off and go straight down.

*******************************************
*                                         *
*    _____________________________________*
*   /                                     *
*  /                                      *
* /     __________________________________*
*/     /    ^                             *
*     /     | (Vector of attack)          *
*    /      |                             *
*   /                                     *
*  /  ~~~~~~_                             *
* /        |_|                            *
*/         | |<-- Cigarette               *
*******************************************
            The Approach

And there you have it. I find this technique works best when the gap is between two-thirds of an inch and one (1) inch wide.



Footnotes:
*There are, however, certain instances where a backseat smoker has access to a small, openable window behind the main window. This provides a place shielded from the wind where one can ash directly out of the car. These are quite rare, however. Specimines are most commonly seen in vans and minivans.

**Source: http://www.physlink.com/Education/AskExperts/ae1.cfm

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