5 Replies Latest reply on Aug 3, 2018 1:47 AM by Joseph Dunfee

    Working newton's cradle question?

    Michael Kennedy

      I'm trying to make a working newton's cradle using hooks to suspend the balls along the frame.  This creates problems I hadn't anticipated with regards to making the object work.  I've fiddled around with it for a long time and I suppose I'll just post the assembly.  I appreciate any feedback.

        • Re: Working newton's cradle question?
          Michael Lord

          Michael,

          I have attached the Assembly but as you are using an Education Version you most likely wont be able to open.

          You needed to make your mates a little more retrained but allow them to pivot where they needed too.

          What I did was:

          Created a couple of sketches on the frame to position the hook.  Mated the centre of the hook to the end point of the sketch

          Sketches.png

          I then created a new part - Pivot.  Which was just a line sketch. Mate the points to the end point of the sketch in the frame.  Mate the point of the other end to the centre of the ball.  This provides the ball to swing in the correct arc

          Pivot.png

          I mated the centre points of the String eyes to the centre line sketch of the hook and ball eyes.  This allows the springs to remain in the correct position when the ball swings

          Sketches.png

          Then mated the planes of the hook & spring so they would remain ridged when all were pivoting

          Mate Plane.png

          • Re: Working newton's cradle question?
            Joseph Dunfee

            I have always been puzzled at the explanations I got about Newtons Cradle, even when I asked a teacher with his Doctorate in Physics.."For every action, there is an opposite and equal reaction".  I always felt it was not sufficient. I think it may even have dissuaded me from studying physics, since I figured I just didn't have the knack to understanding physics.  In the end, I now realize that I had a better knack than my teachers.

             

            And while the "for every action  is part of the explanation  it took the  rise of the internet that gave me  the tools to find someone else that agreed that the traditional answer was not sufficient.  The "for every action", rule does not explain how the balls know that if two balls are used at the beginning of the action, that two balls should be kicked up at the end.  Why not just kick up one ball at double the velocity?

             

            Actually, I don't have enough physics background now to really follow the more complex answers I come across now. But, the basic idea is that the fact that the balls are actually elastic, and do not act instantaneously to transfer their energy to the neighboring balls.  Here is one link to an article that goes into it.

            Newton's Cradle

             

            I, too, only have the student version, so I cannot run the simulation that Michael Lord uploaded   Does it successfully recreate the Newton Cradle's behavior?

             

            -Joe

              • Re: Working newton's cradle question?
                Michael Kennedy

                Hi! I apologize for never responding to this.. I was never able to come back to work on this assembly because of school, work, girlfriends etc. but plan to very soon. I am always floored by how helpful people are on this forum and I appreciate it very much. Once I am able I will let you know how it turns out

                  • Re: Working newton's cradle question?
                    Joseph Dunfee

                    I know this is a late reply, to your late reply.  But, I might suggest modeling the balls as springs.  This might help make the compression of the balls more visible to the observer.  Also, fully constrain the movement so that the balls (spring) can only swing in one dimension.  The two cords that the balls hang from only complicates the physics.  Perhaps have an invisible rod centered above the balls, and then the cords are only cosmetic, and not used in the physics.

                     

                    -Joe