# How Many Horses?

## What I Learned

When I read the article "How Many Horse" I learned that James Watt found out how to make steam engines operate more efficiently. He wanted to start manufacturing and selling his invention, but he didn't know how he could describe how powerful and amazing these engines were. So he decided to compare the power of the steam engine with something that people were familiar with and he chose the power of a horse.

Back then ponies were used to pull ropes attached to platforms that lifted coal to the surface. Watt measured how much the loads weighed then determined how far the ponies could raise them in one minute. Using these measurements, he calculated how much work a pony could do in a minute. Watt found that a pony could do 22,000 ft-lb of work a minute. He figured that the averaged horse was as powerful as 1.5 ponies. He multiplied the power of one pony by 1.5 and called it 1 horsepower.

In other words 1 horsepower is 33,000 ft-lb of work per minute, or 550 ft-lb of work per second. This means that an average horse can lift a 550-lb load a distance of 1 foot 1 second. 1 horsepower translated into watts is 750 W. A 350-hp engine equals the same power as a 262,500-W engine. When numbers get as big as this, you can see that watts aren't a convenient way of expressing the power of engines.

## Mrs. Hillyer's Science Class

We are learning about the world around us.