Re: Repeal of the National Speed Limit Law

in article <95187.072906MICHAEL@MAINE.MAINE.EDU>
Michael Johnson <MICHAEL@MAINE.MAINE.EDU> wrote:

>In article <3ten51$3d4@curly.cc.emory.edu>, lparker@curly.cc.emory.edu (Lloyd R.
>Parker) says:
>>Sorry, but an object in motion possesses an amount of KE equal to 1/2
>>times its mass times its velocity squared.  Basic physics.  To take the
>>object from 10 mph to 0 mph requires removing a certain amount of KE
>>equal to 1/2 times the mass times 100 (1/2m10^2 - 1/2m0^2).  To take the
>>object from 20 mph to 10 mph requires removing KE equal to 1/2 times the
>>mass times 300 (1/2m20^2 - 1/2m10^2).
>>The amount of force you have to use is not a constant -- it will depend
>>upon how much KE you have to remove.

>Hmm.. we really need to do something about these lloyderers. 

Lloyd is right is this case.

>Care to
>cite your reference Lloyd? Unfortunately, I don't have a physics text
>here, but in this case that hardly matters.

Uhhh, you probably should have checked with your physics text.

>Allow me to reiterate. When attempting to make calculations in
>physics (and chemistry) it is important to remember that if the units
>don't come out right, you've made a mistake or some invalid assumptions.

>Let's start with the basics again.

>   W = F * D                                                      (1)

>Work is force times distance. Pretty basic comic book physics.

So far, so good.

>   E = W / T                                                      (2)

>Energy is work over time. Again, basic comic book physics. 

Nope, *power* is work per time.  Energy is work.  Two different names 
for the same thing.  With this wrong equation, there's no point in 
reading the rest of your article.  

Well, I'll just make one more point...
> ... Hm.. there's your velocity squared. But wait a second, how did that
> extra time value get in there?                                              

Too bad you didn't follow your own advice about units: 
    "it is important to remember that if the units don't come out right,

     you've made a mistake or some invalid assumptions."

Phil Mueller  pamuelle@ingr.com  1989 BMW 325i