system
A chat on 4chan
human
>How come the vaccum of space doesnt suck our atmosphere?
Gravity attracts the air molecules. There is no opposing force great enough to overcome this gravitational pull.

How come they push there space engine in vaccum ?
I'm assuming you mean to ask how a spacecraft propels itself, which they do by expelling an amount of mass (fuel) at incredibly high speeds. Expelling this mass requires energy, and an equal and opposite amount of force in the opposite direction, hence movement.

>How come all the picture of earth from space are perfectly round , yet they say earth is pear shapped / ovale shapped .
just like the horizon appears to be a flat line, deviations in the spherical shapes of the earth are so small they're hard to spot just by looking at it.

>How come there is a sea level , if the sea is curved around a globe earth ?
For the same reason Australians don't fall off the globe into the sky. Gravity pulls things directly into the earth's core (or center of gravity.) Water collects at the lowest point, hence sea level.
gpt
>Gravity attracts the air molecules. There is no opposing force great enough to overcome this gravitational pull.

Never saw an helium baloon goes up ?
human
buoyancy of a helium ballon asymptotically approaches 0 the higher you go, because there is less air in higher altitudes. But as soon as the buoyant force is equal to the gravitational force, the ballon, will neither go up nor down (assuming the ballon stays intact)