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CollegeAnarchy t1_ja6a1ay wrote

Reply to comment by InsidiousTechnique in ELI5: Why does farming equipment require such low horsepower compared to your average car? by thetravelingsong

Here is a link to an explanation:

https://www.quora.com/Why-is-air-resistance-roughly-proportional-to-the-cube-of-speed

I understand that link is for air, but the concept Is true for any “fluid”. For all purposes of farm equipment, the soil is a fluid because it flows around the implement.

Actually, a lot of solids can be modeled as fluids when in small pieces. Fluidizing flour, sugar, and sand is how it handled on an industrial scale.

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InsidiousTechnique t1_ja6b1qj wrote

I understand the concept, I doubt it applies to dirt in the same way. There's probably some affect there, but surely not in the same cubic relation.

As an example, you can plow dirt and if you were to go over the same dirt right after and it would take much less force at a constant speed.

It's more about the mechanical bonding and friction than fluid losses in this instance. I'm calling in to question your assertion that dirt acts similarly as a fluid in this specific instance.

How much force does it take to pull a plow through dirt at zero speed? Meaning, if you put a plow in to the dirt, does it take greater than zero force to move it?

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MortalTwit t1_ja6iwq0 wrote

Force = mass times acceleration squared. If you double your speed, you need x4 the force.

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jaa101 t1_ja6fja6 wrote

Note that air resistance is only proportional to the square of the speed, so the heading of the linked article is incorrect. Resistance is a force. It's power that goes with the cube, because it's proportional to force multiplied by speed.

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Travianer t1_ja6pfq0 wrote

The whole truck isn't moving through the medium of dirt though so it's apples to oranges in this case.

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kyrsjo t1_ja6vq2w wrote

That doesn't really matter tough. The force would be the sum of two terms that both goes like v^2, the plow drag and the body air resistance drag. So the total drag force still goes like v^2, and the power (force x velocity) like v^3.

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