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Why Are the Number of Days in a Month Not Equal? |
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When looking at a calendar, one of the first thing that springs forth is the oddity that each month has a seemingly random amount of days. Why are the number of days in a month not equal? And why are they distributed the way they are? To answer that question, we have to look a bit at the history of the modern calendar.
Our calendar, the Gregorian calendar, is a reformed version of the Julian calendar. The Julian calendar, in turn, was a reformed version of the Roman calendar. It was during the reign of Julius Caesar that the calendar was realigned drastically, to make it function somewhat more seamlessly.
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Why does Sound Travel Better with the Wind? |
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You may have noticed that you can hear a sound better if it comes from downwind rather than upwind. We assume that this is because the wind "pushes the sound along." Unfortunately for our intuitions, it can easily be shown that this force is too small to account for the observed effect.
The speed of sound in air is about 760 miles per hour (1223 kph). If a typical wind is blowing at 30 mph, this is only four percent of the speed of sound, meaning that wind can only shorten or increase the distance a given sound needs to travel by that amount. The difference in sound would be too subtle to be detected by the human ear, so obviously this does not uncover the source of the phenomenon.
The actual solution is attached to a property physicists called viscosity. Due to viscosity, wind velocity near the ground is actually slower than velocity at higher altitudes. Collisions between air molecules and the ground give rise to turbulence effects which prevent waves from being transmitted along this air level as quickly.
If air has a uniform temperature, the change in viscosity with altitude causes a sound wave to accelerate along the top layers of air. This causes the sound wave to tip downwards, which makes it more audible to a human listener. This redirecting-phenomenon is called refraction. When sound is moving against the wind, it is refracted in the opposite direction -- upwards. In fact, if you were hovering above the ground in an area upwind from a sound source, you would hear the sound quite clearly, because of the reflection of waves in your direction.
In an area with uniform temperature and no wind, sound waves always travel outwards at equal speeds from the source. As we have seen, this is not always the case.
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Why does china have only one time zone? |
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China is a vast country encompassing a geographic expanse of the equivalent of five time zones, yet it maintains only one time zone. This single time zone is China Standard Time, or Beijing Time, which is Greenwich Mean Time, plus 8 hours (GMT 8). It is also referred to as Coordinated Universal Time, plus 8 hours (UTC 8). UTC is the same as GMT, except it allows for the occasional leap second to satisfy the slight slowing of the earth’s rotation.
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Why is it easy to balance on a bicycle? |
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Although many frustrated but undaunted five-year-old children may disagree, it is remarkably easy for most people to balance on a bicycle. Professional stunt riders can literally perform tricks on every part of a modified bicycle without touching the ground or even pedaling. Once a bicycle and rider take off from a stationary position, it seems like the bike becomes surprisingly stable in a short amount of time.
So why isn't it harder to balance on a bicycle than it apparently should be? The answer lies in the nature of balance and a few laws of physics. The most difficult part of learning to ride a bicycle for many people is creating enough momentum through pedaling in order to allow the bike to stabilize itself. Once a rider learns how to mount a bicycle and distribute his or her weight, the rest is up to the natural physics of the wheels, seat, pedals, brakes and handlebars.
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Why does NORAD track Santa Claus? |
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First, it may help to know what NORAD stands for. NORAD is an abbreviation for the North American Air Defense Command, which was known as CONAD, or the Continental Air Defense Command, until the late 1950s. In 1958, the United States and Canada joined together to form NORAD in order to warn and defend the continent more effectively in the case of an attack. The North American Air Defense Command watches the airways for intrusions such as planes or missiles and warns if any unrecognized object should enter protected airways and more recently, waterways as well.
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Why is rabbit's foot lucky? |
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Considering a rabbit's foot lucky is actually an ancient tradition in much of the world. At least as far back as the 7th century BCE, the rabbit was a talismanic symbol in Africa, and in Celtic Europe, rabbits were considered lucky as well. Thus keeping a part of the rabbit was considered good fortune, and a rabbit's foot was a handy means by which to benefit from the luck of the rabbit.
Many of the beliefs associated with the luck of a rabbit's foot have to do with the types of religions practiced in regions of Africa, Europe and North and South America. Religions based on animism, the sense that spirits inhabited living things attributed power to all kinds of objects that were once living. When spirits were thought to live in animals, plants, rocks and water, then each thing had its own power.
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Rainbows are a striking and beautiful meteorological phenomenon caused by the refraction of light. In order for rainbows to form, the sun must be near the horizon, and there must be a heavy fog, mist, or rain opposite the sun. An observer standing between the sun and the rainbow would see a 180 degree arc of colors which run through the visible spectrum from red to violet. In some cases, if conditions are right, double rainbows will form, with a pale rainbow in reversed colors above the primary rainbow, and in other instances, a fully circular rainbow has been observed, usually from inside an aircraft flying over the Earth.
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Sleep is a natural state of rest for members of the animal kingdom. Scientists have observed the sleep of mammals, birds, reptiles, fish, and amphibians. Although we are still not entirely sure of how sleep works, nor are we convinced that we understand all of the functions of sleep, scientists have become convinced that sleep is necessary to survival.
There are a number of theories about why we sleep and what happens in our bodies and brains during sleep cycles. However, there is not currently one predominant theory. It is quite possible that there is a kernel of truth in each of these theories; that they will all work together eventually to inform a more complete understanding of human sleep.
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Ocean water is salty because it contains high concentrations of dissolved minerals known collectively as salts. Around 3.5% of ocean water is comprised of salts, depending on where in the world one is; equatorial waters tend to be saltier, while northern waters are slowly becoming more fresh. There are a number of factors which make the ocean salty, and scientists are very interested in the salt content of the ocean, because it contributes to the flow of currents through the ocean, in a process known as thermohaline circulation.
One of the reasons that the ocean is salty has to do with the ocean's floor, which contains a huge assortment of minerals and dissolved organic material which is slowly eroded and stirred up by the movements of the ocean. As the ocean eats away at the ocean floor, it increases the salt content. The ocean floor is also constantly renewing itself, another way to make the ocean salty, as seafloor spreading releases even more dissolved minerals into the water, in the form of emissions from hydrothermal vents and cracks in the seafloor.
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