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
If you were moving at 3 km/h, you would come back down to the ground. You move 3 km/h every day.
Orbit is all about going so fast that you fall but constantly miss the ground. Without atmosphere, such as on the moon, you only need to be as high as the highest elevation. So this can be achieved 1 foot from the ground (assuming there is no mountains in your way of course).
From there you can add speed at different parts of your orbit to affect your orbital path at the opposite end. If you have an orbit that is an oval that passes close by the Earth and then goes way out away from it, you move fastest when closest to the Earth. And slowest at the furthest point away.
Basically as you move away, gravity pulls you back. Slowing you down until you turn around and proceed back down your orbit towards Earth.
You need to have enough speed to get past the point where gravity is able to pull you back. At which time you will begin orbitting the sun, which has another escape speed you need to reach to leave it’s orbit.
In space, you are always orbitting something. You need to achieve minimum orbital speed to avoid hitting the ground. And to leave your gravitational body and enter the next, you need to go fast enough to escape that bodies gravity (the sphere of influence).
Technically you dont need to orbit. You can go to space without orbitting. You will come straight back down again. If you went fast enough you could reach escape velocity this way. However it would be INCREDIBLY inefficient as you would be fighting gravity directly the entire time flying straight up. This is why rockets pitch over so soon. Due to the atnosphere, they need to get high enough to avoid getting slowed down. But they are able to get more bang for their buck fuel wise by going sideways rather than straight upwards for long.
The escape velocity is what you’d have to have as you’re on the surface – so, like, if you threw a rock it would have to come off your fingers at 11200m/s to escape.
As you say, if you had a rocket with an insane amount of fuel, you could rise as slow as you wanted (one centimeter per day, or whatever) and eventually escape. But the escape velocity is for if you don’t get a rocket, just one burst at the start, as if you were shot out of a cannon.
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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