Mike from Phoenix wrote in with an observation on how scales work, and how to use this to your advantage.
I noticed at my son’s pinewood derby this morning that his car weighed in at 5.1 ounces (the scale they used read out to one decimal place). I was a bit surprised and did a little bit of sanding – surely not enough to even come close to one tenth of an ounce, I thought. Out of curiousity, I weighed again – this time it came in at 5.0 That got me to wondering if the scale actually rounded to the nearest decimal place. Perhaps he really came in at first at just a hair over 5.05 … then my sanding perhaps got him just a hair under 5.05 ounces and then the scale at that point rounded down to 5.0 ….so, it occurred to me that if my theory is right then it’s sort of a way to add an extra 1/20th of an ounce to one’s car and still be “legal” (and thus maximize the potential energy)
Great thought, Mike. Only quibble I have is that I’d love to see your son doing the sanding and getting the car ready on race day. It is his car, after all.
Comments
8 comments so far ↓
David E. // Jan 27, 2011 at 11:03 am
I taught my kids a technique that seems to utilize your philosophy on weight “gain”. I drill small pilot holes in the back of the car so they can “tweak” the weight at the scales. We have a variety of different screws that allows them to remove / add screws to get the weight as close to the round up number as possible. It also allows them to compensate for weight changes from humidity and scale calibration issues at district.
Aaron Logan // Feb 14, 2011 at 5:59 pm
In reference to Mike’s thoughts on the rounding of digital scales: Although I never got around to testing it myself, I was taught by a very wise physics teacher that digital readouts always round down. Mike’s son’s car would read 5.1 ounces if the weight was anywhere between 5.10 ounces and 5.199999(…) ounces. A digital readout simply doesn’t report the next highest number until it actually reaches that number. So unless I was taught incorrectly, your son’s car could actually weigh 5.099 ounces and still read 5.0 ounces on the scale you were using.
chewbiewan // Apr 14, 2011 at 12:31 pm
I see no problem accidentally being over and still having a reading at 5 ounces, but purposely being overweight and passing inspection is unethical and is cheating. Follow the rules. Is it 5 ounces or not? Are you also going to use illegal axles that can’t be distinguished? What else? Get your speed properly.
RLP // Apr 16, 2011 at 1:15 pm
A Scout should be honest and such a suggested method of going over the weight limit is not legal, moral, or praiseworthy.
mr. e // Jan 3, 2012 at 12:29 pm
a scout is trustworthy.
David // Jan 6, 2012 at 11:31 am
If the district has a scale that only reports to the tenth of an ounce then it is what it is. No one can distinguish the difference at the weigh in of 5.000 ounce versus 5.099 if that is the case. If you have a scale at home that is more precise you will actually be at a disadvantage to others. It is not unethical for you then to play to the scale your district/pack is using as no one is at a disadvantage and everyone is weighing on the same scale.
Gonzo // Jan 19, 2012 at 5:02 pm
I pre weigh my cars very close to 5.0 oz with my wife’s food scale (BTW they are a great gift and they are very convienient come Derby Season… ). I leave one 1/4 hole in the bottom of the car with nothing in it. At the meet I will mix Elmers and saw dust into a light weight putty and drop it into the upside downcar until it comes up to weight. you can remove it as necessary too (until it dries). You can help the other kids come up to weight with this tip as well, then everyone can have agood time.
Hot glue works well for this as well and will also allow you to attach pennies and pewter weights.
PWDdad // Feb 1, 2012 at 5:28 pm
Our district’s rules include the following:
“Official weight will be determined by the official race scale on race day. The weight decision is final regardless of the car’s weight on other scales.”
Their scales read to the nearest tenth. If it reads 5.0 on their scales, it passes. It doesn’t matter if it weighs 5.09 on your scale. It is according to the rules, the same rules everyone in the group uses, therefore it is fair.
We use lead tape from a golf pro shop. We cut nearly square pieces and stick them on near the rear of the car. Each piece is almost 0.01 oz. With about 10 or 12 on the car, if it reads 5.1 just remove them one at a time until it reads 5.0 and then you pass.
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