- 3195 - - KILOGRAM - defined and redefined! The new kilogram's mass corresponds to the energy of 1.4755214 times 10^40 photons that are oscillating at the same frequencies as the cesium 133 atoms used in atomic clocks. Put this on your bathroom scales.
- The “kilogram” isn't a thing anymore. Instead, it's an abstract idea about light and energy.
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- As of May 20, 2021, physicists have replaced the old kilogram, a 130-year-old, platinum-iridium cylinder weighing 2.2 pounds (1 kilogram) sitting in a room in France, with an abstract, unchanging measurement based on quadrillions of light particles and Planck's constant.
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- The “kilogram” is fixed forever now. It can't change over time as the cylinder loses an atom here or an atom there. That means humans could communicate this unit of mass, in terms of science even when we visit other planets.
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- The kilogram is now a simple truth, an idea that can be carried anywhere in the universe without bothering to bring a cylinder with you.
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- The new kilogram weighs, to within a few parts per billion, exactly as much as the old kilogram did. If you weighed 93 kilograms (204 pounds) yesterday, you'll weigh 93 kilograms today and tomorrow. Only in a few narrow scientific applications will the new definition make any difference.
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- It's difficult to rigorously define a “unit of mass” at all.
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- Other fundamental forces have long since been understood in terms of fundamental reality. A second of time? Once, according to the National Institute of Standards and Technology (NIST), it was defined in terms of the swings of a pendulum clock.
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- But now scientists understand a second as the time it takes an atom of cesium 133 to go through 9,192,631,770 cycles of releasing microwave radiation.
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- A meter? That's the distance light travels in 1/299,792,458th of a second.
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- Mass usually measure kilograms in terms of weight. Weight is how much this thing push down on a scale? But that's a measurement that depends on where you perform the actual weighing. That cylinder in France would weigh much less if you brought it to the moon, and even a tiny bit more or tiny bit less if you brought it to other parts of the Earth.
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- The new kilogram is based on the fundamental relationship between mass and energy, the relationship partly spelled out in Einstein's E=mc^2, which means energy is equal to mass times the speed of light squared.
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- Mass can be converted to energy and vice versa. And, compared with mass, energy is easier to measure and define in discrete terms.
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- The physicist Max Planck showed in the year 1900 that E=hv. Planck showed that, on a small enough scale, energy can go up and down, and only in steps. E=hv means that energy is equal to "v", the frequency of some particle, like a photon, multiplied by "h”, the number 6.62607015×10^minus 34 also known as “Planck's constant“.
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- "v" in E=hv must always be an integer, like 1, 2, 3 or 6,492. No fractions or decimals allowed. So, energy is by its nature discrete, going up and down in steps of "h" (6.62607015×10^-34).
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- The new kilogram brings E=mc^2 and E=hv together. That enables scientists to define mass in terms of Planck's constant, an unchanging feature of the universe.
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- An international coalition of science labs came together to make the most precise measurements of Planck's constant yet, certain to within just several parts per billion.
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- The new kilogram's mass corresponds to the energy of 1.4755214 times 10^40 photons that are oscillating at the same frequencies as the cesium 133 atoms used in atomic clocks.
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- It's not the easiest thing to stick on a scale. But, as an idea, it's a lot more portable than a cylinder of platinum-iridium alloy.
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- So much for standards we can hardly measure. Pounds are a lot easier to measure on the bathroom scale. There are just harder to take off. ---------------- Other Reviews:
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- 3032 - KINETIC ENERGY - defined. It all starts with the law of the Conservation of Energy. It is an amazing concept that Energy can neither be created nor destroyed. Energy can only be changed from one form into another. And, the Energy created in the Big Bang is the same Energy we have today. It just got spread out quite a bit in the expansion of the Universe.
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- 3031 - KINETIC ENERGY - the energy of motion? The Universe is in constant motion. how fast is every thing moving in miles per hour. The energy of motion is called Kinetic Energy. The Universe is in constant motion in all directions and everywhere. The Universe must be FULL of energy. Constant motion is a natural state.
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- June 20, 2021 - KILOGRAM - defined and redefined! 3195
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--------------------- --- Monday, June 21, 2021 ---------------------------
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