[Phys-l] what makes the car go? (was: work done by Static Friction)

[John Denker <jsd@av8n.com>]

On 03/15/2007 11:17 AM, John Mallinckrodt wrote:
...
> Unlike the center of mass work and the  
> associated change in kinetic energy, the impulse provide by the road  
> and the (equal) change in momentum of the truck are independent of  
> the choice of reference frame and, as a result, more justifiably  
> viewed as physically connected.


That's 100% true as stated.  However, the questions about
work remain valid questions, and still deserve an answer.

Let's be clear:  There are two categories of question here,
requiring two quite different answers:
 -- energy balance, and
 -- momentum balance.

That is, the question "what makes the car go" has two answers:
 -- the road/tire contact supplies the momentum but not the energy
 -- the onboard motor supplies the energy but not the momentum.

For details on this, see
  http://www.av8n.com/physics/car-go.htm