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

AI Thread Summary
To calculate the spring constant of a PVC pipe for a newspaper delivery crossbow, experimenting with a piece of PVC of the desired length is recommended, as the spring constant can vary based on dimensions. Some participants suggest that using PVC may not be ideal due to its tendency to deform, proposing alternatives like wood or steel for better performance. A resource was shared that discusses the elastic properties of PVC pipes, indicating that the calculation is complex and not straightforward. Additionally, there are suggestions to consider a simpler design, such as a slinging mechanism, instead of a crossbow. Overall, practical experimentation and exploring alternative materials are key steps in the design process.
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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