Re: [Phys-l] Pinewood Derby Car Weight....

[Kathy Daniel <kcdohs@comcast.net>]

My son won our district once and went to the district every time by 
making the car as massive as possible and using liquid graphite on the 
wheel axles.  My understanding is that the more potential energy you 
have from the mass and height of the mass, the more kinetic energy that 
is possible at the end.  The masses cancel out, yes but..... the more 
PE you have the more KE you can get.

My 2 cents.
Kathy

On Feb 24, 2007, at 3:56 PM, von Philp wrote:

> My young son was recently involved in a pinewood derby car race at our
> church.  Since I have never been involved with pinewood derby cars in 
> any
> way, I tried getting some information from the internet.  Most of the
> information I found strongly suggested making the car as heavy as 
> possible.
> One site specifically says "Don't even think about skipping weight 
> addition
> if you want to be race competitive."  and "The weight of your car 
> overcoming
> friction is what will allow to you to win over other cars. You must 
> make
> gravity work for you."
> Now, I really don't want to argue about the fact that heavier cars go
> faster, since the people that wrote those statements probably have a 
> ton of
> experience with this sort of thing and I think they would know.  But 
> I'm not
> sure I fully understand why the greater weight gives the cars an 
> advantage.
> One site says the greater weight gives it more energy and therefore 
> greater
> speed at the bottom, but this is an incorrect reason due to energy
> conservation being independent of mass.  Another site recommends 
> putting
> more weight toward the back because it puts more weight higher giving 
> it
> more (potential) energy.  Again, while these people may know their 
> racing,
> they don't know their physics.
> A finished car will typically weigh around 70 grams or so.  The maximum
> limit is around 142 grams (5.0 ounces).  They recommend adding weight 
> to
> bring it up to as close to the maximum as possible.  Could those extra 
> 70
> grams really make much of a difference (all else being equal!), or 
> could
> they just be speculating without any supporting data.  It would be 
> nice to
> be able to test the same car and add different weight amount to see if 
> the
> race time is affected.
> I'd like to know what the rest of you think about this.
> ~ Ralph von Philp
>
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Kathy Daniel
Oakland High School
Murfreesboro, TN  37130
kcdohs@comcast.net