The bell is a percussion instrument and an idiophone. Many types of bells exist.
A two-stroke engine is a type of internal combustion engine with a cycle of only two (power) strokes.
The battle of the Greek-Persian War became famous for the heroic sacrifice of the Spartan soldiers.
Two meshing gears transmit torque during their rotational motion.
Viking leaders were elected from tribe members by the right of blood or an act of bravery.
Quetzalcoatlus was one of the largest known flying animals of all time.
The battle ended with the overwhelming victory of the Macedonian army over the Persian army led by Darius III.
This animation demonstrates the structure and operation of different types of optical disc drives.
Gladiators were combatants who entertained audiences in fights against each other or wild animals in ancient Roman arenas.
The phosphorus cycle describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.
The oxygen cycle describes the movement of oxygen within its three main reservoirs.
A species of venomous snakes widespread in Europe. Its bite is rarely fatal to humans.
In summer, monsoon winds bring heavy rainfall from the ocean to the continent.
The battleship USS Missouri, first deployed during WWII was also deployed in the Gulf War.
This animation demonstrates the structure and operation of digital cameras.
One of the most important monocot crops.
This animation demonstrates the main sources of soil pollution.
Types of bridges include beam-, arch-, suspension-, cantilever and truss bridges.
This animation demonstrates the geographical locations of the Earth's major cities.
This animation demonstrates how horse chestnut trees change throughout the seasons