Date: Thu, 10 Jul 2003 10:50:36 -0600

Author: Jerry DiMarco

Subject: Re: Jerk

Post:

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The answers offered to this question were convincing enough, but I
wanted to get a better feel for it. So I connected an accelerometer to an
interface and started dropping it and tossing it up in the air. It is an
enlightening experience if you've never done it. On the acceleration graph
(which starts at ~ -9.8 as you hold it steady) there are spikes when you
toss and catch it, and inbetween, while the accelerometer is in flight,
acceleration goes to zero. It was plain to see the change in acceleration
from zero while in flight to -9.8 when held in your hand. One can easily
imagine feeling something, if one was subjected to the abrupt change in
acceleration shown on the graph.
Packing the accelerometer in clay gives even better results. It
seems to reduce some of the noise, and the added weight reduces the
influence of the cable. This could be a more visible way to demonstrate
this effect than the "ball in a thrown tube" type of demo...

Jerry



At 07:28 AM7/6/2003, you wrote:
>As a died-in-the-wool intuitionist (i.e. analytically impaired), often
>throw an anthropomorphic viewpoint into these problems.
>
>Tossing the ball straight up seems to me to be about a simple a problem as
>it can get. Now let's add the highly trained 'Physics Ant' to the demo.
>
>If your students aren't comfortable with reciting the mantra 'The ant,
>while in free-fall is weightless' then you can forget about this explanation.
>
>The ant is weightless for the entire upward journey BUT returns to normal
>weight at the instant that the brakes are applied.
>
>THAT delta a is the jerk. The ant feels it so it is real!
>
>weird!!
>
>(don't embarrass your colleagues TOO much by asking questions about jerk ;-)
>
>
>OK, ya'll, at 12:53 AM -0500 7/6/03, Patricia Sievert wrote:
>>What about the case of a ball tossed straight up. It is experiencing a
>>constant acceleration (g, or 9.81 m/s/s downwards). At the top of its
>>flight, velocity is zero, but acceleration is still 9.81 m/s/s
>>downwards. If at that precise moment, it is "caught", there would be no
>>change in velocity, but there would be a change in acceleration, or a jerk.
>>Pati
>
>--
> .-. .-. .-. .-. .-. .-. .-. .-. .-. .-
> \ / \ / \ N / \ C / \ S / \ S / \ M / \ / \ /
> `-' `-' `-' `-' `-' `-' `-' `-' `-'
>Chuck Britton Education is what is left when
>britton@ncssm.edu you have forgotten everything
>North Carolina School of Science & Math you learned in school.
>(919) 416-2762 Albert Einstein, 1936


<><><><><><><><><><><><><><><><><><><><><><><><><><><><><>

Jerry DiMarco
Manager of Lecture Demonstrations and Instructional Labs
Montana State Univ., Physics
Dept.
Bozeman, MT

Our Motto: "We don't use anything the way it was meant to be used."
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     The answers offered to this question were
convincing enough, but I wanted to get a better feel for it.  So I
connected an accelerometer to an interface and started dropping it and
tossing it up in the air.  It is an enlightening experience if
you've never done it.  On the acceleration graph (which starts at ~
-9.8 as you hold it steady) there are spikes when you toss and catch it,
and inbetween, while the accelerometer is in flight, acceleration goes to
zero.  It was plain to see the change in acceleration from zero
while in flight to -9.8 when held in your hand.  One can easily
imagine feeling something, if one was subjected to the
abrupt change in acceleration shown on the graph.

     Packing the accelerometer in clay gives even
better results.  It seems to reduce some of the noise, and the added
weight reduces the influence of the cable.  This could be a more
visible way to demonstrate this effect than the "ball in a thrown
tube" type of demo...


                                                                        Jerry


 


At 07:28 AM7/6/2003, you wrote:

As a died-in-the-wool intuitionist
(i.e. analytically impaired), often throw an anthropomorphic viewpoint
into these problems.


Tossing the ball straight up seems to me to be about a simple a problem
as it can get. Now let's add the highly trained 'Physics Ant' to the
demo.


If your students aren't comfortable with reciting the mantra 'The ant,
while in free-fall is weightless' then you can forget about this
explanation.


The ant is weightless for the entire upward journey BUT returns to normal
weight at the instant that the brakes are applied.


THAT delta a is the jerk. The ant feels it so it is real!


weird!!


(don't embarrass your colleagues TOO much by asking questions about jerk
;-)




OK, ya'll, at 12:53 AM -0500 7/6/03, Patricia Sievert wrote:

What about the case of a ball
tossed straight up.  It is experiencing a constant acceleration (g,
or 9.81 m/s/s downwards). At the top of its flight, velocity is zero, but
acceleration is still 9.81 m/s/s downwards.  If at that precise
moment, it is "caught", there would be no change in velocity,
but there would be a change in acceleration, or a jerk.

Pati

--

 .-.     .-.    
.-.     .-.    
.-.     .-.    
.-.     .-.    
.-.     .-

    \   /   \  
/   \ N /   \ C /   \ S /   \ S
/   \ M /   \   /   \  
/

     `-'    
`-'     `-'    
`-'     `-'    
`-'     `-'    
`-'     `-'

Chuck Britton
                                  Education
is what is left when

britton@ncssm.edu
            
         you
have forgotten everything

North Carolina School of Science &
Math         you
learned in school.

(919)
416-2762                                  Albert
Einstein,       
1936