Finding the Center of Mass for a Pinewood Derby Car

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Discussion Overview

The discussion focuses on methods for determining the center of mass (CoM) of a pinewood derby car, exploring both theoretical and practical approaches. Participants share various techniques and considerations related to weight placement and design factors that may influence performance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests measuring the shape and mass of each component to calculate their individual center of gravity (CoG) and then the overall value.
  • Another participant proposes balancing the finished car on a knife edge as a simple method to find the CoM.
  • There is a discussion about the optimal placement of weight in the car, with one participant assuming it should be as low and as far back as possible.
  • A method involving hanging the car from a string is mentioned, where the intersection of lines from two different hanging points would indicate the CoM.
  • One participant notes that three different hanging points are needed to accurately determine the CoM in three dimensions, emphasizing the importance of wheel friction and lubrication as primary design considerations.

Areas of Agreement / Disagreement

Participants present multiple methods for finding the CoM, indicating that there is no single agreed-upon approach. Additionally, there is a lack of consensus on the best placement for weight within the car.

Contextual Notes

Some methods rely on assumptions about the car's shape and mass distribution, and the effectiveness of different techniques may depend on specific design choices and materials used.

bart Sherer
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I am trying to determine the center of mass of a pinewood derby car. Any suggestions on how this can be done?
 
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On paper, my measuring the shape and mass of each component - calculating their individual CofG then calculating the overall value.
Or just balance the finished car on a knife edge.
 
Thanks. There is also a lot of discussion as to where the weight in the car shoud be placed. I assume the weight should be placed as low as possible and as far back on the vehicle as possible. Your input is appreciated.
 
Hang the car from the middle of a string, the hanging (free) end of the string will pass through the cm. Do this from 2 different points, the intersection is your cm.
 
To find the center of mass, you actually need *3* different 'hangings' because the car is 3-dimensional. Two will identify the line that passes through the center of mass, the third will reduce it to a point.

In any case, IIRC, the number 1 design consideration is the wheel friction. The wheels must spin freely and be lubricated. Then, the weight and aerodynamics come into play.
 

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