3 Science Questions?

Question

Why would a helicopter have a difficult time flying at altitudes over 6,000 m

2. If The Upper Atmosphere is very thin, why do space vehicles heat up as they enter the atmosphere

3. Why can't gases like helium can escape the earth's atmosphere

THANKS!!!!!!

Answer 1

I think the third one is due to gravitational pull of the earth, gases heavier than hydrogen can't escape the earth's atmosphere.

Answer 2

1) At the risk of oversimplification, because the air has insufficient fluid density and kinematic viscosity at (within the context of the question) very great altitudes to enable the rotor(s) to reliably generate sufficient lift through the Bernoulli effect and pressure differential.

2) Re-entry involves the compression of gases, as the vehicle is slowed by friction from Mach 25+; additionally, vehicles are designed to avail themselves of atmospheric drag by maximizing the plate area during re-entry, in order to prevent the craft from plummeting into the earth.

Parachutes are ineffective at extreme altitude, and useless for the deceleration of such massive and dense forms from hypersonic speeds.

3) They can't achieve escape velocity.