Question

the density of the atmosphere at sea level is 1.29 kilogram metre cube minus cube that it does not change with altitude and how I would the atmosphere extend​

Answer 1

The pressure exerted by a column of height h, density ρ in acceleration due to gravity g

P = hρg

The atmospheric pressure at sea level = 1013.25 hPa = 101325 Pa

h = P/ρg = 101325 / 1.29 x 9.8 = 8 Km (approx)

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But the actual height of atmosphere is several hundred kilometers, because both density and gravity decreases with altitude