Re: Car acceleration

[Bob Sciamanda <trebor@VELOCITY.NET>]

Suppose the car tires were replaced with cogwheels whose projections fit into a slotted, earthbound track.  Then the force mechanism is rigidity, just like the skater pushing off from a wall.  The rubber tires and the slotless road merely substitute a frictional mechanism. 

Of course more than this final mechanism is required in all of these cases (perhaps most importantly an internal energy source), but the force which equates to the car mass times its CM acceleration (in F=ma) is the frictional or rigidity interaction with the external massive object.

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
www.velocity.net/~trebor

----- Original Message -----

From: Herbert H Gottlieb

To: PHYS-L@lists.nau.edu

Sent: Friday, February 01, 2002 11:09 PM

Subject: Re: Car acceleration

BUT .....BOB.....

 

Friction on the car will, by itself, never cause

a car that is stopped at a stop sign on a level road

to accelerate. Evidently something else besides the friction

MUST be involved here.

 

Herb Gottlieb from New York City

(Where road friction by itself does not accelerate our stopped cars)

 

 

 

On Fri, 01 Feb 2002 22:49:23 -0500 Bob Sciamanda <trebor@VELOCITY.NET> writes:
> This is akin to the skater pushing off from a rigid wall.  It is the
> force
> of the wall which accelerates the skater (although the wall is not
> the
> source of the skater's kinetic energy increase).
> In the same way the turning car wheels are "pushing off" from the
> road
> surface.  Operational proof - try it on frictionless ice; now all
> the other
> effects (A,B,D,E) are still operating, but the car will not
> accelerate.  (I
> am assuming a level road.)
>
> Bob Sciamanda (W3NLV)
> Physics, Edinboro Univ of PA (em)
> trebor@velocity.net
> www.velocity.net/~trebor
> ----- Original Message -----
> From: "Gary Turner" <turner@MORNINGSIDE.EDU>
> To: <PHYS-L@lists.nau.edu>
> Sent: Friday, February 01, 2002 6:11 PM
> Subject: Car acceleration
>
>
> > I came across this question in an FCI-type set of questions:
> >
> > A car accelerates forward from a stop sign.  Air resistance slows
> the
> > motion.  What force causes the car to accelerate forward?
> > A) It's weight
> > B) The force of the engine on the tires
> > C) The friction on the car from the road
> > D) The upward force exerted on the car by the road
> > E) The force of the driver on the accelerator pedal
> >
> > When I first read this, I thought I got the answer (which was the
> 'correct'
> > answer).  That is below.  Then I thought about it some more from
> an energy
> > standpoint - now I'm not so sure.  What does the group think?
> >
> >
> >
> >
> >
> >
> >
> >
> > Answer: C
>

 

 

Herb Gottlieb from New York City
(Where it's nice to live but I wouldn't
want to be a tourist here)
herbgottlieb@juno.com