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View Diary: Sales of guns and ammunition surge to record levels with assault weapons sold out in many areas (262 comments)

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  •  Momentum transfer calculation.... (3+ / 0-)
    Recommended by:
    buddabelly, rockhound, pat bunny

    About the force on the kids' backpacks-
    .223 bullet mass is about 3.6 grams (ref). Suppose the kid + backpack weighs about 40 lbs, or 18 kg = 18000 grans. If the momentum is transferred totally to the kid + backpack, that would give you a speed equal to that of the bullet ratioed by the inverse of the masses: 3200 feet per sec times 3.6 divided by 18000, or about 0.64 feet per second.

    If the kid was just holding onto the backpack, which say is lightly loaded at 5 lbs or 2.27 kg = 2270 g, you get a speed of 5 feet per second = 1.5 meters/sec. Still probably not too hard to hold onto given a little notice. If you had to stop that in one foot = 0.3 meters, it would take an deceleration of 7.5 m/sec^2, or about .77 g, implying a force of about 3.8 pounds.

    So provided the backpack absorbed the bullet, it wouldn't be hard to hold onto, and it wouldn't knock the kid down either.

    AR-15s have a very light recoil, and therefore not a lot of striking force. As long as you don't let the bullet enter flesh, of course. That's a whole different ball game. Click only if gore doesn't upset you too much.

    Moderation in most things.

    by billmosby on Sat Dec 29, 2012 at 02:22:40 PM PST

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