Power Converter

Power vs. Energy: What is the difference?

In everyday conversation, we use "Power" and "Energy" interchangeably, but in physics, they are distinct.

• Energy (Joules): The capacity to do work. (Think: The size of the gas tank).
• Power (Watts): How fast you use that energy. (Think: How fast the engine burns the gas).

Power is simply Energy divided by Time. (1 Watt = 1 Joule per second).

The Story of Horsepower

Why do we measure car engines in "Horses"? You can thank James Watt (yes, the guy "Watts" are named after).

In the late 1700s, Watt wanted to sell his new steam engines to coal miners. The miners were using actual horses to pull coal out of the mines. To convince them to buy his engine, he needed to compare it to something they understood.

He calculated that a horse could lift 33,000 foot-pounds per minute. He called this 1 Horsepower. He could then tell the miners: "My engine has 5 Horsepower, so it does the work of 5 horses!" The marketing worked, and the unit stuck.

Mechanical vs. Metric Horsepower

If you buy a car in Germany vs. the USA, the horsepower rating might be slightly different.

Metric horsepower is slightly weaker (about 1.4% less). This is why a car rated at 100 PS in Germany is often rated at 98.6 HP in America.

Common Conversions