Re: That jerk again!

[Leigh Palmer <palmer@sfu.ca>]

Bob Sciamanda wrote:

> > > The immediate effect of applying the brake is to forbid the forward and
> > > rotational motion of the wheel-axle system; the body however will
> > > continue its forward motion until it is brought to rest by the damped,
> > > elastic suspension system which connects it to the wheel-axle system.
> > > The body then moves back as the stressed  (ideally, critically damped)
> > > suspension system relaxes.

Leigh:

> > I presume the wheels to be stationary at the time I apply the brakes.
> > I can't see them, but they "feel" stopped. I presume the body stops
> > when the wheels stop under these circumstances. Some of the assumptions
> > could be incorrect, of course.

Bob:

> Your brakes cannot directly stop the body, they only stop the wheel-axle
> system. The body is stopped by 1)the suspension system which links it to
> the wheel-axle system, and 2)air friction - nothing else that I can see
> in the picture can exert a force DIRECTLY on the body (unless you drag
> your feet on the ground and hold on tight!).

Leigh:

I didn't make myself clear. I assume the body comes to rest at the
same instant the wheels do while the car is coasting uphill in neutral
with brakes off. The only change when the brakes are applied is that
the frame of reference in which the car finds itself has a gravitational
field pointing in a slightly different direction.

Leigh