Tag Archives: horse

Of horses, trucks, and horsepower

Horsepower is a unit of work production rate, about 3/4 of a kW, for those who like standard international units. It is also the pulling force of a work horse of the 1700s times its speed when pulling, perhaps 5 mph. A standard truck will develop 200 hp but only while accelerating at about 60 mph; to develop those same 200 horsepower at 1 mph it would have to pull with 200 times more force. That is impossible for a truck, both because of traction limitations and because of the nature of a gasoline engine when attached to typical gearing. At low speed, 1 mph, a truck will barely develop as much force as 4-5 horses, suggesting a work output about 1 hp. This is especially true for a truck pulling in the snow, as shown in the video below.

Here, a semi-truck (of milk) is being pulled out of the snow by a team of horses going perhaps 1 mph. The majority of work is done by the horse on the left — the others seem to be slipping. Assuming that the four horses manage to develop 1 hp each (4 hp total), the pull force is four times a truck at 1 mph, or as great as a 200 hp truck accelerating at 50 mph. That’s why the horse succeed where the truck does not.

You will find other videos on the internet showing that horses produce more force or hp than trucks or tractors. They always do so at low speeds. A horse will also beat a truck or car in acceleration to about the 1/4 mile mark. That’s because acceleration =force /mass: a = F/m.

I should mention that DC electric motors also, like horses, produce their highest force at very low speeds, but unlike horses, their efficiency is very low there. Electric engine efficiency is high only at speeds quite near the maximum and their horse-power output (force times speed) is at a maximum at about 1/2 the maximum speed.

Steam engines (I like steam engines) produce about the same force at all speeds, and more-or-less the same efficiency at all speeds. That efficiency is typically only about 20%, about that of a horse, but the feed cost and maintenance cost is far lower. A steam engine will eat coal, while a horse must eat oats.

March 4, 2016. Robert Buxbaum, an engineer, runs REB Research, and is running for water commissioner.

Theodore Roosevelt jumps fence, rides moose

One of my favorite presidents, a liberal Republican, a friend to immigrants and  the poor, but not opposed to prosperity either. Though some thought he might be crazy, none thought he was a wuss, and none messed with him or the USA when he was in office. Yes, that’s the president riding a moose, jumping a fence, and camping on a cliff with John Muir.

theodore-roosevelt-mooseTheodore Roosevelt Jumps Fence on Horsetheodore-roosevelt-yosemite

 

January 16, 2013 R.E. Buxbaum. If you liked this, you might want my insights into a famous incident where Teddy Roosevelt got shot on the way to giving a speech. Instead of treatment, he gave the 2 hour speech and survived. Why did he do this? How did he survive it?