Joule, a unit of energy or work in the metric system of measurement. By definition, one joule is the work done when a force of one newton is exerted over a distance of one meter. (A newton is the force necessary to give a mass of one kilogram an acceleration of one meter per second per second.) The joule is an absolute unit—that is, it is based on mass rather than weight and hence is independent of the force of gravity. Another, less commonly used metric unit of energy or work is the erg. One joule equals 10,000,000 ergs. In the traditional English system of measurement, the foot-poundal is used in place of the joule. A foot-poundal is equal to approximately 1/25 of a joule.
They may seem like a fun water sport or a noisy nuisance, but whatever your stance on personal watercraft, there's no denying they pollute. So how bad are they?
Shedding light on dark energy has been a bit of a challenge for today's astronomers. What dark energy actually is goes beyond our present scientific understanding.