zdenek@heathcliff.columbia.edu (Zdenek Radouch) (12/11/86)
>Consider the following thought experiment: > > Take 2 identical cars and place them nose to nose. Rig the > accelerators of both so that you can give equal acceleration > to each. Now slowly increase the accelerations of the two > cars. Assuming that there is no slippage of the wheels, the > cars will remain motionless.... Note that if the cars are nose to nose (or as you pointed out motionless) you cannot "slowly increase the acceleration". They are not moving let alone accelerating. If there was no slippage of the wheels the engine couldn't run. You have to take care of conservation of energy even in a thought experiment. The work output of the engine can't just disappear. The cars are not moving so the energy delivered by the engine has to go somewhere else. The wheels must slip but the car will be motionless because the forces are balanced. zdenek zdenek@cs.columbia.edu or ...!seismo!columbia!cs!zdenek
dant@tekla.tek.com (Dan Tilque;1893;92-789;LP=A;60jB) (12/13/86)
In article <4087@columbia.UUCP> zdenek@heathcliff.columbia.edu.UUCP (Zdenek Radouch) writes: > I write: >>Consider the following thought experiment: >> >> Take 2 identical cars and place them nose to nose. Rig the >> accelerators of both so that you can give equal acceleration >> to each. Now slowly increase the accelerations of the two >> cars. Assuming that there is no slippage of the wheels, the >> cars will remain motionless.... > >Note that if the cars are nose to nose (or as you pointed out motionless) >you cannot "slowly increase the acceleration". They are not moving let alone >accelerating. If there was no slippage of the wheels the engine couldn't run. >You have to take care of conservation of energy even in a thought experiment. >The work output of the engine can't just disappear. The cars are not moving >so the energy delivered by the engine has to go somewhere else. The wheels >must slip but the car will be motionless because the forces are balanced. > >zdenek You're right. I'll change the experiment. Let the two cars bumpers which start to crumple as soon as the accelerator is pushed. The cars will then have very low velocities (like the continental plates I'm comparing them to). The rest of the engines energies go into crumpling the bumpers. My point was that the velocities (and thus kinetic energy) of the cars or continents cannot be used to determine how much crumpling should take place. (I have no doubt that you'll correct me if I'm wrong.) Dan Tilque dant@tekla.tek.com inews fodder inews fodder inews fodder inews fodder inews fodder inews fodder inews fodder inews fodder inews fodder inews fodder
sdp@omssw1.UUCP (Scott Peterson) (12/18/86)
In article <4087@columbia.UUCP> zdenek@heathcliff.columbia.edu.UUCP (Zdenek Radouch) writes: >>Consider the following thought experiment: >> >> Take 2 identical cars and place them nose to nose. Rig the >> accelerators of both so that you can give equal acceleration >> to each. Now slowly increase the accelerations of the two >> cars. Assuming that there is no slippage of the wheels, the >> cars will remain motionless.... > >Note that if the cars are nose to nose (or as you pointed out motionless) >you cannot "slowly increase the acceleration". They are not moving let alone >accelerating. If there was no slippage of the wheels the engine couldn't run. >You have to take care of conservation of energy even in a thought experiment. >The work output of the engine can't just disappear. The cars are not moving >so the energy delivered by the engine has to go somewhere else. The wheels >must slip but the car will be motionless because the forces are balanced. Unless the cars had automatic transmissions. Then the slippage would occur in the powertrain. Engine output would become heat and motion of hydraulic fluid. The car with the best torque converter would win. ... but then maybe that's beyond the scope of the problem. -- Scott Peterson, Intel Corp., Hillsboro, OR, ...!tektronix!ogcvax!omssw1!sdp
coleman@sask.UUCP (12/30/86)
> >> Take 2 identical cars and place them nose to nose. Rig the > >> accelerators of both so that you can give equal acceleration > >> to each. Last I heard acceleration is a vector therefore they would both move in the same direction. But then isn't this whole argument becoming directionless! -- Geoff Coleman | BITNET: Coleman@sask College of Engineering | UUCP: {utcsri,ihnp4}!sask!skul!geoff University of Saskatchewan | Compserve: 76515,1513 just a number Saskatoon, Saskatchewan | voice: (306) 966-5415