Why are traffic lights red, yellow, and green? Because they cannot be mistaken for each other and we have learned that red means danger and green means go. When they were invented, traffic lights used white to mean “go”, green for “caution” and red for “stop”. The first traffic lights were not made for cars. […]
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Why can we eat lettuce and spinach, but we can’t eat leaves and grass? We can’t eat leaves and grass because of the cellulose and silica they contain. There are several different ways of getting energy. Plants photosynthesize and make energy, which they store in their cells. Herbivores eat the plants to get the energy
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Why were alarm clocks the first consumer goods to stop being rationed during World War 2? Because, as you would expect, people couldn’t wake up in time to work. People have used many different methods to wake themselves up over the centuries. Some people relied on church bells. Some people used elaborate systems with candles
When were latitude and longitude invented? Latitude in about 600 BC and longitude in AD 1736. Latitude are the horizontal lines that measure your distance to the north or the south of the equator. Longitude are the vertical lines that measure your distance to the east or west of 0, which has been set as
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Why do we say north, east, south, and west? The cardinal directions north, east, south, and west came about because of the position of the sun in the sky. Nobody has any idea when the idea of cardinal directions came about. Early civilizations would have had no need for directions such as north and south
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Where did the circus come from? The modern circus was invented in 1768, but the idea of a show in an amphitheater goes back thousands of years. The word “circus” comes from Greek, through Latin into English. It simply means “ring” or “circle” and the Romans used them to show horse and chariot races, battle
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How are tower cranes assembled? By raising themselves up and adding in a piece at a time. There are many different types of cranes, but they are divided into two categories: mobile and fixed. We are looking at the cranes that are used to build skyscrapers today, and they are fixed tower cranes. Any type
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Why does an elastic band stretch? Because it is made of long chains of polymers that would rather be tangled together than straight. Rubber is famous for its ability to expand and return to its original size without any damage. There are natural rubbers and synthetic rubbers. The English word “rubber” was first used in
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How does antibiotic resistance happen? Bacteria develop the ability to survive an antibiotic, which is then passed on to future generations. The antibacterial power of some moulds has been known about since 1874, possibly even earlier. In 1897, Ernest Duchesne published a paper about the ability of moulds to kill bacteria. Alexander Fleming noticed that
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How does a skeleton key work? By removing all of the parts that would get caught on the wards. Skeleton keys are also known as pass keys or master keys. They are called “skeleton keys” because all of the main parts of the key have been stripped off and only the skeleton is left. People
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