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



We have years of experience with pine wood derby competitions in our family. The PE to KE explanation already given is what we used to help our sons do quite well. We never spent much time on balance and stability or they may have done even better. If the starting gate holds the cars at an angle (can't picture it any other way), even placing more of the weight towards the back of the car can make a difference.
Mentioning the extreme case, our daughter is younger than both our boys and one year we made a car for her that was WAY over the 5 oz. weight limit. The night before the official races our Scout Pack had trial runs. The only rule being that you couldn't test your car against someone in your same category. Sara had a blast racing against all the little boys as her plain boxy-looking car won every time, and not just by a little bit. It wasn't until she let one of her friends hold her car that they caught on. Pati

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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