How many pounds are in a gallon?

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Discussion Overview

The discussion centers around the conversion of gallons to pounds, specifically in the context of water, and the weight-bearing capacity of a 2x4 wooden beam. It involves both theoretical and practical considerations regarding density, material properties, and specific conditions affecting these calculations.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the conversion from gallons to pounds depends on the substance being measured and whether a US gallon or an imperial gallon is used.
  • It is emphasized that density or specific gravity is necessary for accurate conversions from volume to weight.
  • One participant states that the weight of 1 US gallon of water is 8.33 pounds, leading to a total weight of 749.7 pounds for 90 gallons of water.
  • Another participant raises the question of how much weight a 2x4 can support, indicating that this depends on various factors including material type and orientation.
  • There is a discussion about the strength of different types of wood, noting that an oak 2x4 is stronger than a balsa 2x4, and that flaws in the wood can affect its load-bearing capacity.
  • One participant mentions the importance of considering the area moment of inertia when calculating the allowable load for a 2x4.
  • Another participant refers to specific values for the elastic modulus of pine wood, suggesting that safety margins should be included in calculations related to structural integrity.

Areas of Agreement / Disagreement

Participants generally agree that the weight of a gallon depends on the substance and that density is crucial for conversion. However, there is no consensus on the exact load-bearing capacity of a 2x4, as multiple factors influence this calculation, leading to competing views on the topic.

Contextual Notes

The discussion highlights the need for specific information regarding the material and conditions when calculating weight and load capacity, as well as the variability in wood properties that complicate such calculations.

darkwolf
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How many pounds are in a gallon? (I need exact amount). What is the Formula any and all for gallons to pounds.
my e-mail is darkravewolf@sbcglobal.net
 
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That entirely depends upon what it is a gallon of. Also, you need to specify whether it's a real gallon or a Yank gallon.
 
You need the density or specific gravity of what you are trying to calculate the volume of. There is no direct conversion from weight to volume.
 
i need to know the poundage of 90 us water gallons
 
as well as how much weight can a 2x4 hold up
 
The first is easy if you go with pure water at room temperature; mineral content and temperature differences vary it. One cc of water weighs one gram. Just convert your units to find how many cc's there are in a gallon (the information is readily available), and then convert your result from grams to pounds.
The second question is another that requires far more information to answer. An oak 2x4 is a lot stronger than a balsa one. It also matters which way it's oriented. Lastly, there are almost always flaws of some type, be it knots or warpage or whatever.
 
Weight of 1 US gallon of water is 8.33 pounds. 90 gallons would weigh 749.7 pounds.

As far as how much weight a 2x4 can hold, it depends on how the 2x4 is supporting weight as well as the material involved, but you can probably assume construction grade pine. Note that a 2x4 is not 2 inches by 4 inches either.
 
The 2x4's allowable load will also greatly depend on it's orientation, i.e. it's area moment of inertia.

Wood, like most composites, is a bit of a tough material when dealing with calculations of this type. There are so many variables that can effect it's true strength that you really have to be careful. Plus, it is not an unreasonable assumption that the material is non-homogeneous, which most standard derived equations like [tex]\sigma = \frac{M c}{I}[/tex] are based on.

According to Mark's Handbook, it looks like the range for elastic modulus of a standard kind of pine with a 12% moisture content is between 1200 and 1400 ksi (Table 6.7.2, pg. 6-115). Personally, I would include a healthy safety margin in that if this calculation is going to be for something around people or can cause damage.
 
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