I read that to escape Earth's gravity a rocket must travel at 40.000 KMH.
Why can't the rocket travel at just 20.000 KMH and just take twice as long to escape the gravity.
I never understood this thing.
Links to external sites would help too.
Thanks.
Why can't the rocket travel at just 20.000 KMH and just take twice as long to escape the gravity.
I never understood this thing.
Links to external sites would help too.
Thanks.
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It isn't necessarily the speed a rocket needs to achieve to escape. That isn't the point.
Rockets CONTINUOUSLY propel forward...they don't "count" in the direct derivation of escape speed.
Escape speed is derived for a FREE PROJECTILE escaping. "Free projectile" means not acted upon by anything other than gravitation. I.e. no propellant, no jet engine thrust, no air drag. Just a simple object gone ballistic.
It still is IMPORTANT when applying it to a rocket, because it still represents how we need to SIZE the amount of fuel needed per unit payload mass. You still need to provide the rocket with enough energy that it hypothetically could instantly achieve escape velocity when it is initially launched (if all propellant is released simultaneously...which it isn't).
Rockets CONTINUOUSLY propel forward...they don't "count" in the direct derivation of escape speed.
Escape speed is derived for a FREE PROJECTILE escaping. "Free projectile" means not acted upon by anything other than gravitation. I.e. no propellant, no jet engine thrust, no air drag. Just a simple object gone ballistic.
It still is IMPORTANT when applying it to a rocket, because it still represents how we need to SIZE the amount of fuel needed per unit payload mass. You still need to provide the rocket with enough energy that it hypothetically could instantly achieve escape velocity when it is initially launched (if all propellant is released simultaneously...which it isn't).
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The rocket undrgoes a power match against gravity power As the rocket climbs above the atmosphere it usess less and less power to move.Thus the rocket is launched at different power stages.
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Throw a stone up and it will fall back on ground. If you fire a Diwali rocket (fireworks) it might go still higher up. You'll inherently learn to see that you need to have a stronger arm that throws up such that it goes up in the shortest time and not as you said. It is so because if you linger on longer, the Earth's gravitational pull (that is relentlessly present all the time) would pull it back (down) to itself.
Acceleration that is the change in velocity, with change happening in shorter time. Escape velocity if exceeded will ensure that the falling off that velocity (called deceleration, opposite to acceleration that is due to Earth's gravity)with every passing second, shall not eventually reduce it to zero. If you provide a velocity greater than the escape velocity, by the time the velocity gets reduced to zero, you are fairly outside the Earth's gravitational pull (& atmospheric air friction) that with that residual velocity the object will remain above (actually it tries to fall back in a long arc, at the end of which it misses the Earth that has limited extent)
Acceleration that is the change in velocity, with change happening in shorter time. Escape velocity if exceeded will ensure that the falling off that velocity (called deceleration, opposite to acceleration that is due to Earth's gravity)with every passing second, shall not eventually reduce it to zero. If you provide a velocity greater than the escape velocity, by the time the velocity gets reduced to zero, you are fairly outside the Earth's gravitational pull (& atmospheric air friction) that with that residual velocity the object will remain above (actually it tries to fall back in a long arc, at the end of which it misses the Earth that has limited extent)