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A Sci Fi Question for the Physics Nerds

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  • A Sci Fi Question for the Physics Nerds

    I was thinking about space battles and this question came to mind. If you had two space battleships, for reference sake about the size of WWII battleships and one of them fired a projectile weapon roughly the size of a 16" shell and that shell strikes the opposing ship, would the impact cause the stricken ship to lurch to one side?

    I was thinking about how in space you have no gravity and no weight and thus even large object can be moved with less force than normal. And since a ship in space is in a void rather than sitting in the water wouldn't there be less force holding it in place? And thus wouldn't some of the kinetic energy of the shell impact thus push it over? If so, how much?
    A new life awaits you in the off world colonies; the chance to begin again in a golden land of opportunity and adventure!

  • #2
    I think the size of the projectile is immaterial - it's the energy it transmits that is important which is a combination of its mass and speed and the degree to which the target is moved will depend on its inertia - again mass and speed.
    Human history becomes more and more a race between education and catastrophe (H G Wells)
    Mit der Dummheit kaempfen Goetter selbst vergebens (Friedrich von Schiller)

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    • #3
      F=MA. Now do the math.
      I was married for two ******* years! Hell would be like Club Med! - Sam Kinison

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      • #4
        Originally posted by Pirateship1982 View Post
        I was thinking about how in space you have no gravity and no weight and thus even large object can be moved with less force than normal.
        This is not true.

        All things have mass. Weight is a factor of mass and proximity to another, larger mass. If you put something massive in space, it may have no weight but it still has mass. And moving something with mass requires the same amount of force.

        The equation is F=ma where F = force, m = mass, and a = acceleration. Basically, given any object, you need the same amount of force to get it to accelerate the same amount regardless of whether its on earth or in deep space.

        So, to answer your question: If the battleship sized object would lurch on earth, it will lurch in space. If it wouldn't, then it won't.

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        • #5
          Originally posted by DingBat View Post
          This is not true.

          All things have mass. Weight is a factor of mass and proximity to another, larger mass. If you put something massive in space, it may have no weight but it still has mass. And moving something with mass requires the same amount of force.

          The equation is F=ma where F = force, m = mass, and a = acceleration. Basically, given any object, you need the same amount of force to get it to accelerate the same amount regardless of whether its on earth or in deep space.

          So, to answer your question: If the battleship sized object would lurch on earth, it will lurch in space. If it wouldn't, then it won't.
          I was about to say the same thing, but I expect weight vs mass was a typo.
          How to Talk to a Climate Skeptic: http://grist.org/series/skeptics/
          Global Warming & Climate Change Myths: https://www.skepticalscience.com/argument.php

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          • #6
            What Would Kimball Kinnison Do?
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            • #7
              Originally posted by OpanaPointer View Post
              What Would Kimball Kinnison Do?
              That's a blast from the past.

              Credo quia absurdum.


              Quantum mechanics describes nature as absurd from the point of view of common sense. And yet it fully agrees with experiment. So I hope you can accept nature as She is - absurd! - Richard Feynman

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              • #8
                Plus the explosive force force of the projectile assuming it wasn't simply solid shot.

                Also, if you were to compare it with a ship in water, if the shell landed on say the port side of the ship from an angle of something close 90 degrees, there would be resistance to starboard movement by the resistance of the water acting against the starboard hull. In space this wouldn't exist.

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                • #9
                  Originally posted by DingBat View Post
                  This is not true.

                  All things have mass. Weight is a factor of mass and proximity to another, larger mass. If you put something massive in space, it may have no weight but it still has mass. And moving something with mass requires the same amount of force.

                  The equation is F=ma where F = force, m = mass, and a = acceleration. Basically, given any object, you need the same amount of force to get it to accelerate the same amount regardless of whether its on earth or in deep space.

                  So, to answer your question: If the battleship sized object would lurch on earth, it will lurch in space. If it wouldn't, then it won't.
                  You're forgetting about friction of which there will be none in the vacuum of space but if you hit a ship in air and water your're missile is effectively not only applying force to the target but through it to the air and water to which it has contact which will defectively absorb some of the energy this reducing the movement of the target.

                  This lack of friction in space is why even a low powered ion drive if applied over enough time to a threatening asteroid could still move it away from a collision course.
                  Last edited by MarkV; 04 Mar 16, 04:16.
                  Human history becomes more and more a race between education and catastrophe (H G Wells)
                  Mit der Dummheit kaempfen Goetter selbst vergebens (Friedrich von Schiller)

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                  • #10
                    Originally posted by MarkV View Post
                    You're forgetting about friction of which there will be none in the vacuum of space but if you hit a ship in air and water your're missile is effectively not only applying force to the target but through it to the air and water to which it has contact which will defectively absorb some of the energy this reducing the movement of the target.

                    This lack of friction in space is why even a low powered ion drive if applied over enough time to a threatening asteroid could still move it away from a collision course.
                    "Meh"

                    Friction is a reactive force. If the ship doesn't "lurch" in water, it's still probably not going to "lurch" in space.

                    Remember also, your shell was dealing with friction as it traveled through the air to the target on earth, whereas it would not when fired in space. The amount of energy delivered to the target would probably be noticeably larger as well, for that reason.

                    But the answer is still "meh".

                    If you're really interested in measuring inches of lurch, then this might be a significant conversation. I didn't really get the sense that the OP was being that picky.

                    The underlying statement of the OP which was that it takes less force to move an object in space than it does on earth is still incorrect.

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                    • #11
                      Originally posted by Pirateship1982 View Post
                      I was thinking about space battles and this question came to mind. If you had two space battleships, for reference sake about the size of WWII battleships and one of them fired a projectile weapon roughly the size of a 16" shell and that shell strikes the opposing ship, would the impact cause the stricken ship to lurch to one side?

                      I was thinking about how in space you have no gravity and no weight and thus even large object can be moved with less force than normal. And since a ship in space is in a void rather than sitting in the water wouldn't there be less force holding it in place? And thus wouldn't some of the kinetic energy of the shell impact thus push it over? If so, how much?
                      Even better, the battleship that fired the shell will be shoved sideways with a force equal to that required to launch the weight of the shell.
                      Quis Custodiet Ipsos Custodes? Who is watching the watchers?

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                      • #12
                        Originally posted by DingBat View Post
                        "Meh"

                        Friction is a reactive force. If the ship doesn't "lurch" in water, it's still probably not going to "lurch" in space.

                        Remember also, your shell was dealing with friction as it traveled through the air to the target on earth, whereas it would not when fired in space. The amount of energy delivered to the target would probably be noticeably larger as well, for that reason.

                        But the answer is still "meh".

                        If you're really interested in measuring inches of lurch, then this might be a significant conversation. I didn't really get the sense that the OP was being that picky.

                        The underlying statement of the OP which was that it takes less force to move an object in space than it does on earth is still incorrect.
                        Its never going to lurch in space. In micro gravity the projectile will travel on a straight line and hitting the target will propel that target in the same direction. The speed of that travel will depend upon the inertia of the target a product of its mass and speed and the energy of the projectile which if non explosive will be a function of its mass and speed. If explosive will depend on the nature of that explosive. In a vacuum where there is no friction to slow it the target will continue to move in the direction in which it is propelled at that speed until it hits another object, fires its engines, is trapped in the gravity well of some larger body or some combination of all three. It will not lurch. Basic Newtonian physics
                        Human history becomes more and more a race between education and catastrophe (H G Wells)
                        Mit der Dummheit kaempfen Goetter selbst vergebens (Friedrich von Schiller)

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                        • #13
                          Originally posted by Mountain Man View Post
                          Even better, the battleship that fired the shell will be shoved sideways with a force equal to that required to launch the weight of the shell.
                          Unless it is fired from a recoilless gun (ie with a counterweight or gas jet) or is rocket propelled
                          Human history becomes more and more a race between education and catastrophe (H G Wells)
                          Mit der Dummheit kaempfen Goetter selbst vergebens (Friedrich von Schiller)

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                          • #14
                            This would be a simple conservation of momentum application

                            http://www.physicsclassroom.com/clas...tion-Principle

                            The impact would indeed cause the target to "lurch"

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                            • #15
                              Interesting points guys.
                              A new life awaits you in the off world colonies; the chance to begin again in a golden land of opportunity and adventure!

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