Quote (card_sultan @ Jul 5 2016 12:43pm)
Except im not the idiot who doesnt believe the assumption that gravity is a magical force that holds all the water and air in place while we spin at 1000 mph , rotate around the sun at 66,600mph and spiral around the milky way galaxy at 450,000 mph while we expand into the universe at the speed of light but a simple hot air balloon is stronger than all that force.
The problem with the above is these are velocities or speeds, which you are comparing to acceleration (gravity). To compare them we need to calculate the accelerations produced by these rotations:
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Earth's rotational velocity at equator: 1000 mph, in si units that is about 450 m/s.
centripetal acceleration: v^2/r
centripetal acceleration on Earth do to its rotation: {450 (m/s)}^2/{6,400,000 m}≈
0.03 m/s^2, that is about 0.3% or about 1/300th of the acceleration produced by gravity (Earth to surface of Earth).
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Earth's orbital velocity (sun): 66,600mph -> 30,000 m/s
centripetal acceleration on Earth do to its orbit of sun: {30,000 m/s}^2/{1.5*10^11 m} ≈
0.006 m/s^2, about 0.06% of the acceleration produced by gravity (Earth to surface of Earth)
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Earth's orbital velocity (around galactic core): 450,000 mph - > 230,000 m/s (I think the actual rate is a bit larger, but this is in the right ballpark).
centripetal acceleration on Earth do to its galactic orbit: {230,000 m/s}^2/{2.5 * 10^20 m} ≈
2*10^(-10) m/s^2, a ridiculously small number.
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So the 3 velocities you mentioned give rise to an acceleration (when summed, but I'll give you the benefit of the doubt here) of less than half of 1% of the acceleration associated with gravity near the surface of the planet (about 10 m/s^2). This is why these accelerations are typically ignored on back of the envelope calculations. This is also why you can't feel them, but you can feel gravity (you know, the thing you say does not exist).