Science Buddies: "Ask an Expert"

When zip lining, the person working forgot to reset the break when I zipped. The block of wood wasn't far enough out on the rope. So when i never stopped, I flipped up and hit the ceiling of the fort. In scientific terms, what happened to me?

First, the safest way to install zip lines is so that have enough sag in them so that the final section is going uphill so that you get some gravity braking. The ends of a zipline should also have a padded landing zone below so you can safely let go and just drop in case of trouble.

Your description of the accident is incomplete so I'm going to make some assumptions which may or may not be correct. In any case, as you started down the zipline you accelerated. Your momentum (aka inertia force) at any point in time is 0.5 * your mass * your velocity * your velocity. Assuming that the zipline carriage ran into a hard stop at the end, it stopped and you didn't and Newton's first law of motion covers this situation. Your hands on the zipline carriage stopped so your hands became a pivot point for your arms and body to convert your linear forward motion into a pendulum action so your body swung around and your feet went upward until you ran into something or the gravitational force equaled your momentum force at which point you started to swing back the other way.

very clear explanation. thanx a lot

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