Nelson Mandela was South Africa's first black president.

To become a liquid, hydrogen must be cooled to a temperature of -423 Fahrenheit.

Rockets were first invented in the early 1200s by the Chinese as their "fire-arrows."

Louis Braille got the idea for Braille from night-writing, a form of code for soldiers, invented by Charles Barbier.

When air confined to a cylinder is suddenly compressed, its temperature rises.

In an internal-combustion engine, a mist of liquid fuel is mixed with oxygen and burned to release chemical energy.

The first practical steam engine was invented in 1712.

Nearly 1 third of Tanzania is set aside for national parks and game preserves.

The capital of the Democratic Republic of Congo, Kinshasa, was formerly named Leopoldville.

Egypt was the first Arab nation to make peace with Israel.

Chemical energy is stored in the bonds that hold molecules and chemical compounds together.

Most deserts receive less than 10 inches of rainfall per year.

To find out what your weight would be on the moon, divide your own weight by 6.

Your body has 100 oil glands and 700 sweat glands per square inch of skin.