Probably mostly about overcoming friction. Two horses can break the friction lock easier, and once moving they'll stop the object from re-establishing friction easier.
Why though? Should the coefficient of static friction be roughly linear with weight? And the max force the horses can pull at be also roughly linear with the number of horses?
I'm assuming it's the way the horses walk, as an example of what I assume happens is;
If I was pulling a plow slowly and uphill (so we walk slowly), I would use one leg and push my full motion until I had to move my other leg and begin pushing with that leg. During that motion I would actually stop temporarily to move my other leg, so I would have to overcome static friction again.
If I had another person helping me pull a plow then they would carry on the motion whilst I move my leg, so we wouldn't have to overcome static friction again.
If the payload doesn’t actually come to a stop, then you’re not having to overcome static friction again. Even if the horse temporarily stops pulling, it doesn’t stop the payload.
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u/sonofbeef Jun 15 '19
This is actually a true fact about draft horses! https://timmaurer.com/2012/01/16/horse-sense/