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As opposed to underground mines, in open-pit mines the layers covering coal are removed, coal is extracted on the surface.
Farmhouses in the Middle Ages were simple, single-storey structures built from earth, mud and wood.
The Earth is divided into 24 time zones. Standard time is the time used within time zones.
Scoliosis is a medical condition in which a person's spine has a lateral deviation.
The arms are moved by flexor and extensor muscles.
This animation demonstrates the five regular three-dimensional (or Platonic) solids, the best known of which is the cube.
Entertaining and spectacular animation to practise orientation in space.
Edges, diagonals and faces of a cube can be identified by its vertices.
The Möbius strip and the Klein bottle are special two-dimensional surfaces with only one side.
The conic section is a plane curve that is created when a right circular cone is intersected by a plane.
The German engineer Otto Lilienthal was the first person to make successful flights with a glider designed by himself.
A fuel cell provides environment-friendly electric energy produced by the chemical reaction between oxygen and hydrogen.
This animation explains the technology of shale gas extraction.
Keeps were typical buildings in the Middle Ages, also built independently from castles.
Bones of the lower limbs are connected to the trunk by the pelvis.
Articulated lorries play an important role in road transport.
Several analogous types of eyes have developed independently through convergent evolution.
The American Civil War was fought between the Confederacy and the Union.
Edison´s invention records and plays sound from a cylinder, while Berliner´s apparatus uses a disc.
A type of sugar found in mammalian milk.