This only happens with an automatic transmission.  The crankshaft is
connected to what is known as a torque converter.  There is no physical
connection between the crankshaft and the wheels, instead there is a
"liquid" connection.  When the crankshaft hits a certain rpm, it causes the
liquid to spin.  The energy is transferred through the liquid to the other
side of the torque converter where the power is transferred to the wheels.
The car won't move until the gas pedal is pushed far enough to overcome the
friction and gravity holding the car back.
-----Original Message-----
From: Sean Breheny <shb7@CORNELL.EDU>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Monday, June 15, 1998 6:32 PM
Subject: Re: Water injection


>While on the subject of engines and cars, I would like to ask a slightly
>related OT question that has been bugging me for a long time: How can a
>car sit still on a hill with the engine holding it from rolling
>backwards? The engine, of course, needs to keep its crankshaft turning in
>order not to stall. However, the wheels are not turning in this case.
>Somehow, the torque is being transferred from the engine to the wheels
>while alowing them to move independently of the crankshaft. How is this
>possible? What component in the drivetrain allows this?
>
>Thanks,
>
>Sean
>