What is the sound barrier? When a plane passes the sound barrier it produces a booming sound. Sound travels at a certain speed depending on the altitude. When the plane flies faster than sound its wing undergoes great stress. This causes a shock wave which...
Who invented the elevator? In the early 19th century elevators existed but they were used mostly for freight. The hoisting drums of the elevators were turned by steam power. But elevators became popular only after Elisha Graves Otis invented a safety device to prevent the...
How big were Tyrannosaurus’ teeth? The teeth of Tyrannosaurus were 18 cm long. They had a very sharp point — as sharp as a razor — to stab prey. They also had rough, saw-like edges to tear through flesh. Adults had around 50-100 teeth. Teeth...
What is an airship? An airship is actually a balloon shaped like a cigar. It is filled with gas, usually helium. A gondola or cabin and engines are suspended under the balloon. The Germans developed airships called Zeppelins in the 1910s.
What makes a light bulb glow? A light bulb consists of a very thin wire called a filament. It is connected to a metal plate at the bottom of the bulb in two places. When we switch on a lamp, electricity flows through the plate...
What is the advantage offered by electromagnets? Electromagnets will lose their magnetic properties when the current is turned off. This makes it useful in large and small machines. While ordinary magnets can lift very heavy loads in factories it is difficult to make them release...
How does a compact disc work? A compact disc or CD has a plastic surface on which sounds are stored in binary code as small holes called pits and flat areas called lands. A laser beam can be used to read these. When the laser...
How was the Inca Empire destroyed? The Inca Empire was destroyed by the Spanish adventurer, Francisco Pizarro. It was a prosperous and well-governed empire. When Pizarro arrived, a fight for power was going on between Huascar and his half-brother, Atahualp Pizarro killed the latter while...
What is static electricity? When we rub things made of amber or plastic it will pick up electrons from our clothes or hair. This gives them a positive charge. Then if we happen to touch something with a slightly negative charge a small spark often...
When was coffee brewed for the first time? Initially coffee was used without being brewed. The fruit of the tree was used by east African tribes as food. The berries were roasted or prepared with animal fat and eaten. Coffee was probably first grown in...
