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It's the name of the international standard system of measurement, and it's also called the SI unit, taking the abbreviation from French, which had the strongest influence when the metric system was established. The metric system defines a total of 7 units of measurement. Second, Meter, Kilogram, Ampere (electric current), Kelvin (temperature), Mole (amount of substance), Candela (luminous intensity) However, significant errors were found in the initial definition, so the standard was recently changed and redefined. This is because if we were to adhere to the original definition, the familiar units of measurement currently in use would have to be completely changed. Therefore, we chose to keep the currently used units of measurement and redefine them based on a standard that will never change. The current redefined standard involves overly long numerical notations, so only the standard will be presented, and the exact numbers will not be shown. 1. Second Initial Definition: 1/86400 of the Earth's one rotation period (a day) Current Definition: Redefined based on the frequency of Cesium-133 Reason for Change: The Earth's rotation period is slightly slowing down due to the Moon's gravitational pull. (This was explained in the explanation of synchronous rotation)

Have you ever poured tea, only for the liquid to stream down the spout and spill onto the floor? What seems like a simple mistake is actually one of fluid dynamics' famous unsolved problems: the 'Teapot Effect'. This occurs due to a battle between 'surface tension,' which makes the liquid cling to surfaces, and 'inertia,' which makes it want to keep moving forward. The fluid's velocity and subtle pressure changes around the spout's curve prevent the liquid from falling freely, causing it to flow back up along the outer wall. Even world-renowned physicists have spent nearly 70 years devising complex equations to mathematically explain this everyday inconvenience. It turns out that sophisticated fluid dynamics are hidden within this seemingly trivial phenomenon.

Last time, I introduced the definition of meteorological seasons. I'll introduce a city that was about to enter autumn. According to the Korea Meteorological Administration link, Dongducheon's daily average temperature dropped below 20°C starting from September 9th. However, if you actually calculate the 9-day moving average using Excel: Date Avg Temp Moving Avg 6 21.8 19.97 7 21.8 19.58 11 18.0 20.12 The moving average from the 6th to the 14th reached below 20°C... However, starting from the 17th, the average temperature began to rise again, and the moving average from the 11th to the 19th started to exceed 20°C again. If it hadn't warmed up, I might have declared it autumn on the 6th, but it was reversed because the weather continued to warm up afterward. The criteria for the Korea Meteorological Administration is when the temperature drops below 20°C and does not exceed 20°C again. So, autumn is still a long way off...

Did you know that 'Dry Water' exists, where your hand doesn't get wet even when you put it in water? Dry Water is 95% real water, but it appears as a white powder. This is because the surface of tiny water droplets is coated with silica (sand component) nanoparticles, preventing the droplets from clumping together and causing them to bounce off each other. Although it doesn't leave any moisture when touched by hand, it boasts a unique chemical property of absorbing gases at an incredible speed, much faster than liquids. This Dry Water is gaining significant attention as a futuristic eco-friendly material that can efficiently capture carbon dioxide to combat climate change, or safely store and transport hazardous chemicals.

For a long time, it was identified as the cause of Chinese Restaurant Syndrome, and research was conducted, but MSG's toxicity could not be proven. Instead, it was only proven to be safer than salt. - Comparison of Salt and MSG Toxicity LD50 is a representative measure of toxicity, indicating the dose at which half of the test subjects die in animal experiments. Salt: 3g, MSG: 19.9g (when administered to a 1kg rat) This means MSG is 6.6 times less dangerous. However, the reason salt isn't considered poisonous is that an adult weighing 60kg would have to consume 180g at once to die, which is an unlikely amount. Since MSG is used in even smaller quantities than salt, it is even safer in terms of toxicity. - The Relationship Between Restaurant Broth and MSG Restaurants advertise that they don't use MSG and make broth by boiling meat, vegetables, and seafood in water. Chemically speaking, this is the process of making MSG. Actual seasoning factories perform the same process. The only difference is that broth is simply boiled, while MSG undergoes a process of concentration and powdering.

Did you know that even diamonds, seemingly the hardest and most eternal substance in the world, can burn up and disappear into the air? In the 18th century, chemist Antoine Lavoisier used a large magnifying glass to focus sunlight and heat a diamond in a sealed container. The experiment showed that the diamond burned away without a trace, leaving only carbon dioxide in the container. This revealed the great chemical fact that diamonds are the same 'pure carbon' as graphite or pencil lead. So, the gem symbolizing eternal love turned out to be a lump of carbon that turns into gas and flies away when exposed to fire.

Periodic Table: A table that organizes elements according to their chemical properties. Group: A vertical column in the periodic table; elements in the same group share similar chemical characteristics. Period: A horizontal row in the periodic table; elements in the same period have the same number of electron shells. Octet Rule: A rule stating that atoms tend to gain, lose, or share electrons to achieve a full outer shell of eight valence electrons, which is considered a stable state. However, starting from the 4th period where transition metals appear, the outer shell expands, extending to the 18-electron rule. Orbital: A theory that explains the shape of atomic orbitals. Each orbital can hold a maximum of two electrons. Period 1: Uses the 1s orbital and can only hold 2 electrons. Contains only two elements: H and He. Periods 2 & 3: Have 8 valence electrons (s(2)p(6)). Periods 4 & 5: Have 18 valence electrons (s(2)p(6)d(10)). Periods 6 & 7: Have 32 valence electrons (s(2)p(6)d(10)f(14)).

The oxygen we breathe every day is a colorless and odorless gas that is invisible to the eye. However, when oxygen is cooled below -183 degrees Celsius and turned into a liquid, it takes on a vivid sky-blue hue. Even more surprising is the fact that liquid oxygen is attracted to magnets. This is because the unpaired electrons within oxygen molecules form a unique structure, giving them magnetic properties. If you flow liquid oxygen between powerful magnets, you can witness the fascinating phenomenon of it hovering in the air and sticking firmly to the magnets. It turns out that this gas, which seems ordinary because it's always around us, was actually a surprising chemical substance possessing a blue color and magnetism.

The coldest place in the universe is the 'Boomerang Nebula,' located 5,000 light-years away from Earth. The temperature here is -272 degrees Celsius, just 1 degree above absolute zero, where all molecular motion ceases. Interestingly, this nebula is even colder than the 'Cosmic Microwave Background' radiation (which is -270 degrees Celsius), the leftover heat from the Big Bang. In essence, it's a unique natural freezer, colder than the space of the universe itself. The reason for this extreme cold is that the dying star at the center of the nebula is expelling gas at a staggering speed of 164 km/s, causing it to expand. Due to the principle of adiabatic expansion, the gas rapidly cools, creating the most uniquely extreme cold in the entire universe.

- Regions where typhoons rarely occur Left Image: Accumulated Tracks of Tropical Cyclones Right Image: Ocean Currents 1) Equator: Does not occur due to zero Coriolis force. 2) Southeast Pacific: Water is cooled by a cold current, resulting in low evaporation. However, in years with El Niño, sea surface temperatures rise, potentially leading to hurricane formation. The most recent hurricane occurred in 2016. 3) South Atlantic: The eastern part is influenced by a cold current, reducing evaporation. The western part has a continental shape, limiting the area where storms can develop and making it difficult for them to intensify. 4) Mediterranean Sea: The sea is too small for storms to develop. However, a storm was recorded in 2011. 5) High-latitude regions: Does not occur due to low water temperatures.