6 ms·

Escape velocity is 25,020 mph (6.95 mps), so not completely surprising. Note that escape velocity applies to a situation without continued propulsion and also

• sd9 7mo ago
  Not surprising if you know that. Pretty surprising to me who didn’t.
  • layer8 7mo ago
    Maybe you’ll like this too: The Earth’s speed around the sun is around 67,000 mph. So it moves significantly faster than the rocket, though not orders of magnitude. The solar system itself moves at 43,000 mph relative to its local neighborhood. But speed is always just relative to some frame of reference. Acceleration, on the other hand, is absolute, and so might be the more interesting thing to look at here.
    • lionkor 7mo ago
      Acceleration is change in speed, so it is, by its very nature, relative just like speed is. If I fall, I might accelerate at G meters per second, relative to the earth, but I don't absolutely accelerate. If the earth decelerates at the same time, I'm now both accelerating an decelerating. It's relative.
      • layer8 7mo ago
        It’s absolute in the sense that you can determine your acceleration without any external reference. You feel a certain force (like what you feel in an elevator). That’s your acceleration. You don’t accelerate relative to Earth, or relative to anything else. You accelerate relative to when you wouldn’t be accelerating (your inertial rest frame, a state of free fall). If you are in space accelerating and the Earth would decelerate (which is just an acceleration in the other direction), you would still feel exactly the same force (minus Earth’s gravity, to the small extent you’d still feel it), and people on the Earth would feel the Earth’s acceleration. (For them it would feel like “down” isn’t perpendicular to the Earth’s surface anymore, or as if the Earth’s surface was tilted.) When you sit on a chair on Earth, the pressure you feel on your butt is your acceleration upwards. If there was no chair and no ground (and no air), so that you’d be in free fall, that’s when you’d have zero acceleration. Your inertial rest frame is the trajectory you’d take in free fall. When you’re sitting on a chair, or lying in bed, or standing on the ground, you’re accelerating upwards relative to that rest frame, and that’s the pressure you feel on your butt, or on your body, or under your feet.
        • deleted 7mo ago
          [deleted]
        • reactordev 7mo ago
          "You feel a certain force" is that true in zero-g?
          • peterleiser 7mo ago
            Yes
            • JumpCrisscross 7mo ago
              Well, technically no. Zero g, as in zero gravity, is force less. We don’t have a region of space we know of that can block gravity.
          • vscode-rest 7mo ago
            [dead]
        • marcus_holmes 7mo ago
          I am in a gravitational field. I have no idea what my acceleration is, I just know that I feel 1G (I could be falling in a stronger gravity and only feel 1G, or I could be climbing in a weaker gravity and feel 1G). The only way of determining it is to see if I'm moving relative to the stuff around me. Even then, that's not definite - I could be in an elevator and everything around me is also accelerating. I'm not disagreeing with you, I'm just pointing out that there are circumstances where "you can determine your acceleration without any external reference" isn't true. You might even say that this is relative to your circumstances ;)
          • qubitcoder 7mo ago
            You can always hold an accelerometer in your hand. If you did so now, assuming you're on Earth's surface, it'd register approximately 9.8m/s/s pointing in the upward direction. You could also perform one of many historical experiments, such as dropping an object from an elevated height with careful timing, or rolling a round ball down a gently sloped track, and so on.
      • kd0amg 7mo ago
        Think of it more as "speed is the indefinite integral of acceleration" with the extra constant denoting a choice of inertial reference frame.
• bibelo 7mo ago
  Thank you for that precision "without continued propulsion", because when talking about rockets, physics teachers always talk about escape velocity, as if it was an absolutely necessary condition to escape earth's gravity. But can't you escape gravity slower, just by going higher and higher at lower speed? Like a plane? (ie not vertically, but at an angle)
  • Rover222 7mo ago
    No, the absolute minimum speed IS required. Anything below that and you’re just making your orbit elliptical.
    • pedrocr 7mo ago
      That seems wrong. If you have a way to maintain enough propulsion for long enough you can escape the gravity well at any arbitrarily low speed. You "just" need to maintain that speed long enough for the escape velocity from the gravity well to go below it as it diminishes with distance from the mass.
      • Rover222 7mo ago
        Oh yeah, 1.01 Gs of endless propulsion will work. I was just arguing in the context of existing technology.
  • atombender 7mo ago
    If you don't accelerate, my understanding is that you will slow down. In other words, it takes more and more energy to escape orbit. Eventually, if you don't accelerate, your speed drops to zero and you "fall back down". Escape velocity is about how much energy you put into your motion, not the velocity as such.
• dreamcompiler 7mo ago
  Exactly. Your rocket can escape the earth at the speed of a slow elevator if you burn the engines continuously and you can carry an infinite amount of fuel and your fuel weighs nothing. Since those constraints are impossible to meet in the real world, we have to get going fast enough to coast most of the trip on inertia after the fuel runs out.