The colors of visible light, often referred to as ROY G BIV (for red, orange, yellow, green, blue, indigo, and violet), are a small portion of the entire electromagnetic spectrum. Light can be thought of as a stream of packets of energy called photons.
The United States has a mixed economy and has maintained a stable overall GDP growth rate, a moderate unemployment rate, and high levels of research and capital investment. Its seven largest trading partners are Canada, China, Mexico, Japan, Germany, South Korea, and the United Kingdom.
The United States is the world's largest national economy, representing 22% of nominal global GDP and 17% of global GDP (PPP) .The United States' GDP was estimated to be $17.914 trillion as of Q2 2015. The U.S. dollar is the currency most used in international transactions and is the world's foremost reserve currency.Several countries use it as their official currency, and in many others it is the de facto currency.he American colonies went from marginally successful colonial economies to a small, independent farming economy, which in 1776 became the United States of America. In 180 years, the US grew to a huge, integrated, industrialized economy that made up around one fifth of the world economy.