How do I Calculate the Spring Constant of a Piece of PVC pipe?

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Discussion Overview

The discussion revolves around calculating the spring constant of a piece of PVC pipe for the purpose of designing a newspaper delivery crossbow. Participants explore the feasibility of using PVC pipe as a spring material and consider alternative designs for the delivery mechanism.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes their project of creating a newspaper crossbow and seeks guidance on determining the spring constant of a PVC pipe.
  • Another participant suggests that a 0.3-meter length of PVC may be too short for a bow and proposes an alternative design using an extension to sling the newspapers.
  • A different participant questions the necessity of the specified distance of 1.83 meters, suggesting that tossing the newspaper might be sufficient.
  • Another participant argues that PVC is not an ideal material for a spring due to its tendency to deform and recommends considering wood or steel instead.
  • One participant provides a resource link regarding the elastic properties of PVC pipes but notes that the question is complex and suggests experimentation as a viable approach.

Areas of Agreement / Disagreement

Participants express differing opinions on the suitability of PVC pipe as a spring material and the design of the delivery mechanism. There is no consensus on the best approach or material to use.

Contextual Notes

The discussion highlights the complexity of determining the spring constant for PVC and the potential need for empirical testing. Participants acknowledge that the choice of material and design may significantly impact the effectiveness of the proposed solution.

JosephStevens99
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Okay so, recently I got a job with my local newspaper delivering newspapers to make some money while deciding how I want to continue my educational career (I already have some college under my belt but I'm taking a semester off). All the newspapers have to be at the houses by 6 am so in order to save time I wanted to make a newspaper crossbow which will deliver the newspapers a consistent 1.83 meters from my car window (which is 1.22 meters above the ground). I already calculated how much force it would take to launch newspapers of varying mass the fixed distance of 1.83 meters and am starting to design the crossbow.

My question is how would I go about finding the spring constant of a piece of PVC pipe approximately 0.3 meters long so that I can properly design my crossbow. Do I have to go out and get a piece of PVC pipe that long (or I guess short) and do some experimenting or is there a resource I can look up online to find the spring constant of PVC piping by length (and the diameter) of the pipe?
 
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Welcome to the PF. :smile:
JosephStevens99 said:
piece of PVC pipe approximately 0.3 meters
That sounds way too short to be used as a bow. Maybe look at making an extension that you can use to sling the papers instead?

(kind of like the ball slingers used for playing "fetch" with dogs, but with an end tuned for newspapers...)

https://img.chewy.com/is/image/catalog/151628_PT1._AC_SL1500_V1550270910_.jpg
1571422519530.png
 
berkeman said:
Welcome to the PF. :smile:

That sounds way too short to be used as a bow. Maybe look at making an extension that you can use to sling the papers instead?

(kind of like the ball slingers used for playing "fetch" with dogs, but with an end tuned for newspapers...)

https://img.chewy.com/is/image/catalog/151628_PT1._AC_SL1500_V1550270910_.jpgView attachment 251416

Hmmm, I'll definitely consider this at it seems like a much easier solution than building a whole crossbow. Thank you for your time and input!
 
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JosephStevens99 said:
deliver the newspapers a consistent 1.83 meters from my car
Is that the right distance? I'd think you can easily toss a newspaper that "far" - it's only six feet.
 
gmax137 said:
it's only six feet
I was guessing he needs to toss it that far out the passenger window while driving, but I could be wrong...
 
PVC is a poor choice for a spring. It will deform too easily. How about wood or steel?
The answer to your question is here:
https://www.researchgate.net/publication/281786040_Elastic_properties_of_PVC_pipes
It's not a simple question, so you won't get a simple answer. As you suggest, getting some and trying it is probably the best approach.
 

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