Re: That jerk again!

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Wed, 19 Nov 1997, Jim Riley wrote:

> First, the car is at rest, not moving, has never been moving, and I apply
> the brakes.  Obviously I will feel nothing.

Yup.

> Second, the car has been moving but under the influence of gravity the car
> and its contents have come instantaneously at rest.  Call this time t=0.   I
> apply the brakes at this instant.  Is there any physical difference between
> the objects involved at this instant and the previously mentioned condition?
> Answer-No.  Therefore I should feel nothing at this time either..  

Nope.  There *is* a difference.  The difference is the very large jerk
(time derivative of the acceleration) which *is* felt and causes distinct
discomfort. 

John
-----------------------------------------------------------------
 A. John Mallinckrodt      http://www.intranet.csupomona.edu/~ajm
 Professor of Physics    mailto:ajmallinckro@csupomona.edu
 Physics Department       voice:909-869-4054
 Cal Poly Pomona            fax:909-869-5090
 Pomona, CA 91768-4031   office:Building 8, Room 223