Gravity, one of four forces, is an important topic to life on earth. We all presume that gravity is around 9.81 m/s2 ever since we have gotten physic education at middle school. Ever wondered how does gravity change through Earth surface and into the core of the Earth ? I supposed that there was either linear or parabolic changes into the core of the Earth so far. Nevertheless, the truth is partially different that lets us down. How does gravity change through Earth surface ? Effective gravity on the Earth's surface varies by around 0.7%, from 9.7639 m/s2 on the Nevado Huascarán mountain in Peru to 9.8337 m/s2 at the surface of the Arctic Ocean. In large cities, it ranges from 9.766 in Kuala Lumpur, Mexico City, and Singapore to 9.825 in Oslo and Helsinki. The precise strength of Earth's gravity varies depending on location. The nominal "average" value at the Earth's surface, known as standard gravity is, by definition, 9.80665 m/s2. and what about change into the Core of the Earth ? The weight of things increases slightly as we go deeper until we get inside the Outer Core, and then gravity finally begins to decrease. See the blue line on the plot below. If the earth had uniform density, then gravity would decrease linearly all the way down to the center, as shown by the green line. But in fact, the Earth's core is substantially more dense than the outer layers (mantle and crust), and gravity actually increases a bit as you descend, reaching a maximum at the boundary between the outer core and the lower mantle. Within the core, it rapidly drops to zero as you approach the center, where the planet's entire mass is exerting a gravitational pull from all directions. Earth's gravity according to the Preliminary Reference Earth Model (PREM). Two models for a spherically symmetric Earth are included for comparison. The dark green straight line is for a constant density equal to the Earth's average density. The light green curved line is for a density that decreases linearly from centre to surface. The density at the centre is the same as in the PREM, but the surface density is chosen so that the mass of the sphere equals the mass of the real Earth. What is mathematical description about gravity change ? What about planet's gravitational pull ? Finally we can make a comparison among planets. The stunning point of this compasion is that gravity of sun is 10x higher than the highest planet. If you were living on sun, you could reach 843km/h maximum speed within 100m free fall. Sources:
[1]http://physics.stackexchange.com/questions/18446/how-does-gravity-work-underground [2]https://en.wikipedia.org/wiki/Gravity_of_Earth [3]http://www.npl.co.uk/reference/faqs/how-can-i-determine-my-local-values-of-gravitational-acceleration-and-altitude-(faq-pressure)
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