can someon eexplain to me how this escape speed of roughly 40.000km/h works? , do i need this only at the start or at the end of escaping the earth,? cant i just leave it with lets say 3km/h. im totally lost pls help
In: Physics
You usually measure escape velocity in km/s so you get 11.19 km/s for the earth.
That is the speed a ballistic projectile needs to have at the surface of the earth to escape the earth’s gravitational field. That is if you ignore air resistance.
The speed would drop because of gravity so the projectile only have the speed on the surface
A ballistic projectile is a non propelled object so it would be the required speed if you fire an object from a cannon on the ground. It is not the speed propelled object like a rocket needs to have, it could in theory move at any speed if you have enough fuel to sustain it.
It is still relevant for a rocket it needs to be able to accelerate the payload to that velocity. It is a minimum acceleration because you have air resistance close to the ground and gravitational losses later. A rocket that could accelerate an object to 1km/s has a delta-V of 1km/s. Delta-V is the capacity to change velocity, the delta of indicate a change in something.
Gravitational losses is because you need to overcome gravity for any acceleration before you reach orbit. Take a rocket that has enough trust to levitate in the air, it is using a lot of fuel but it does not result in any acceleration. So you loose 1g o acceleration from gravity. So a rocket with the trust of 2x the weight only accelerates at 1g but at 3x the trust you accelerate at 2g.
The result is that minimum fuel if you ignore air resistance, structural strength and max trust you like to do all acceleration at the ground.
Moving straight out at 1m/s would be very fuel-efficient because it takes a long time and the rocket engine need to compensate for gravity the whole time. I you move at 10m/s the time is 1/10 and a lot less fuel it needed.
In practice, you often launch to an earth orbit first. A low earth orbit haw a speed of 7.4km/s and you need a rocket tha cant accelerate you to 9.4 km/s to reach it. The 2km/s difference is from gravity loss and air resistance. From that point you can if you like take a long time to add enough energy to leave earth gravitational field. The speed will get lower when you move farther away because of how orbits works.
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