Sound waves consist of alternate compressions and expansions. So the speed of a sound wave is completely dependent on how fast the wave bounces back from the previous compression. In simple terms, the less compressible the medium is, the faster the waves bounce back. Moreover, the denser the medium, the slower the acceleration of the molecules which in turn slows down the compressions.
Air is highly compressible, whereas water is 15,000 times less compressible and 800 times denser than air. Hence, the speed of sound in water is higher than that of air. In case of a diamond, the speed of sound is so high because it is it highly incompressible but relatively light. This is the maximum speed that sound travels under normal conditions. (1, 2)
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7 The easternmost point of Brazil is closer to Africa than it is to the westernmost point of Brazil.
The easternmost point of Brazil is closer to Africa than it is to the westernmost point of Brazil. Image Credit: Google Maps
The easternmost point of Brazil (mainland) is Ponta do Seixas and its westernmost point is Serra do Divisor. Brazil’s easternmost point is 1,826 miles from Freetown, Sierra Leone, which is located in West Africa. Surprisingly, Ponta do Seixas is 2,637 miles from Serra do Divisor. So, the easternmost point of Brazil is closer to Africa than its westernmost point. Hence, proved! (1, 2)
8 It is believed that 90% of U.S. dollar bills in the cities have Cocaine on it.
Yes, that’s true. But the reason four out of five bills have cocaine on them is NOT because the bills were used to snort cocaine. It is also NOT because the bills have passed through the hands of drug dealers. No, there is another reason behind this fact. Cocaine is a very fine powder. When a dollar bill contaminated with cocaine is processed through a counting machine, some traces of the drug are passed on to the other bills which came in contact with it. The same happens when a contaminated bill makes its way through an ATM. (source)
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9 Between 2011 and 2013, China used more cement in three years than the US did in the entire 20th century.
Between 2011 and 2013, China used more cement in three years than the US did in the entire 20th century. Image Credit: Forbes
This statistic is so unbelievable that it sounds fake. The fact sounds unbelievable because the 20th century was the time when the US built all its roads, bridges, dams, skyscrapers, and transportation networks. So let’s turn to the actual numbers to see if the fact holds true.
According to the U.S. Geological Survey, between 1901 and 2000, the US utilized 4.5 gigatons of cement. On a more surprising note, according to the International Cement Review, China utilized 6.4 gigatons of cement between 2011 and 2013, which is just three years. That much cement can build a parking lot as big as Hawaii.
One reason for this immense utilization of cement can be attributed to China’s historic growth rate. China’s growth rate was much faster than US’s growth rate in the 20th century. Every year about 20 million Chinese residents relocate to cities. This number is more than the population of New York, Chicago, and Los Angeles combined. Moreover, many of the houses in the US are made from wood. But China suffers from a lack of lumber. Also, China has an enormous cement manufacturing industry! (source)
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10 Shoelaces untie themselves because the knot is subjected to forces of up to 7G with every step that the wearer takes.
Although we deal with shoelaces getting untied by themselves all the time, the reason behind it has been studied for the first time. A team of researchers at the University of California led by Oliver O’Reilly, a mechanical engineer, were the first ones to study the reason behind this common occurrence.
They devised a simple experiment to watch at a close range how the shoelaces get untied. A test subject was made to walk on a treadmill. Accelerometers were attached to her shoes that enabled the scientists to measure the acceleration, or gravitational force, acting on the knot with each step.
With the help of slow-motion video, the team discovered that there are two stages in which the knot comes undone. The first involves the gradual loosening of the knot with each step taken by the wearer. Next, there comes a sudden purge when the knot comes undone completely. What surprised the researchers was the gravitational force that was acting on the shoelace during each stride.
The accelerometer measured a gravitational force of up to 7G. This is more than the force created by the most powerful roller coaster. O’Reilly explains, “The flapping motions back and forth actually increase inertial forces on the free ends. That exacerbates the imbalance. Then they pull through, and then the shoelace has failed.” (source)
