Creating projectiles out of household objects


Here are two examples of people turning small everyday items into projectiles without any mechanical aids. In the first case, a man throws ordinary playing cards in a way that can slice vegetables.

In the second slow-motion video, a Shaolin monk throws a needle through a plate of glass.

It would be interesting to see a study of the physics of phenomena like these that confound our sense of hardness.

Comments

  1. says

    Ricky Jay’s book “Playing Cards as Weapons” was a goofy 1970s classic (I still have my copy)
    In it, Ricky demonstrated throwing individual playing cards over buildings, through things, and with extreme precision and gratuitous nudity. It’s good to see there are still playing card ninjas out there…

  2. Jared A says

    It would be interesting to see a study of the physics of phenomena like these that confound our sense of hardness.

    Hurray for materials science!

    Hardness is indeed a difficult phenomenon to talk about. Our intuitive idea of hardness is really several related phenomena that are quite different microscopically.

    By any measure of hardness that I know, all steels are softer than all silica glasses, so in this case it’s nothing to do with the hardness of the materials that allows the needle to puncture the glass. Honestly, I am not sure precisely what the right mode for this is, but the principle feature is the brittleness of glass.

    So, for example, diamond is the hardest substance under normal conditions, so it cannot be scratched by other materials, but anyone could smash one with a hammer. Hardness =/= resistance to breaking.

  3. 'Tis Himself says

    a man throws ordinary playing cards in a way that can slice vegetables…a Shaolin monk throws a needle through a plate of glass.

    Everyone needs a hobby.

  4. Sheila G says

    PLEASE, everyone, be careful who you share this with; we wouldn’t want the TSA to see it!

  5. Francisco Bacopa says

    Can we be sure that wasn’t Hollywood sugar glass in the second video? I would really think that has got to be very thin glass. I have built aquariums and aquarium fixtures, so I think I have a pretty good sense of how glass works. I could be wrong, though.

    I’ve seen enough weird destruction during hurricanes to not be surprised by playing cards cutting fruit. One strange thing that happens during a hurricane is that the heavy translucent plastic used on internally lit signs can be completely shattered by the storm while the florescent lights inside are unharmed. The lights even still work a few days later when the power comes on, so you have maked florescent lights inside a frame.

    Sometimes materials don’t work the way we think they will.

  6. lochaber says

    Not much of a claim, but I wouldn’t be surprised if the vid checks out ok. (Not that I even bothered to google it or anything…)…

    I think the more interesting thing w/ the second vid is that there is just a little hole w/ a halo of cracks, as opposed to a shattered sheet. -I’m guessing this is a combination of getting enough kinetic energy in such a small object (via throwing it really damned fast), and getting it to impact end first (to concentrate all of that energy on a tiny point).

    I’ve done a bit of work with aquariums and such as well (probably nowhere near the amount you have…), and while the amount of weight they can hold is amazing, I think one of the important factors is that it’s evenly distributed over the entire surface.

    playing card thing is interesting too. I’ve never witnessed it, but have heard it talked about (mostly on the internet) for.. years, maybe decades?
    seems that they frequently use watermelons, though this guy seems to have diversified into apples and… zucchini?
    anyways, I’m guessing there is something to the structure of fruits/squash/melons that make them usefull to these displays. (soft, easily damaged structure, yet seems firm when we handle them?)

    granted, just propelling a chunk of paper in a manner like that is a pretty impressive feat, but I’m rather doubtful it could inflect much damage (I’m sure if he chucked one at your eyeball, you’d have a pretty unpleasant day, but I don’t think you’d suffer serious long-term damage from it).

    I’d be more wary of them if they were sinking cards into rolled up newspapers or 2x4s

    still, way more skill/talent then I could ever manage, and kinda cool to watch.

    anyways… interesting vids.

  7. Norm says

    No one said the cards were paper.
    Plastic playing cards are heavier and stiffer than paper cards.

    And I’d like to know how thick the glass is, too.

  8. starskeptic says

    “I think the more interesting thing w/ the second vid is that there is just a little hole w/ a halo of cracks, as opposed to a shattered sheet. -”

    Exactly what would happen with very thin or Hollywood sugar glass – I think Francisco’s got this one covered…

  9. Jared A says

    From a materials perspective there is a huge difference between very thin “regular” glass and sugar glass. I don’t know much about the strength or hardness of sugar glass, but both parameters are likely orders of magnitude lower than regular glass. If the material in the video is sugar glass then you have grounds to dismiss it as special effects.

    However, one shouldn’t dismiss mere “thin glass” as something lesser than thick glass. They have the same properties intrinsic properties. What’s incredible is that the needle busts through the glass and keeps going.

    IIRC, the halo cracks are characteristic of this type of failure unlike the type of failure where the projectile bounces back (like spalling; actually usually the projectile just stops, but from a momentum perspective that’s almost like bouncing back). The latter is what you are used to in your every day experience and what tends to cause glass to shatter into many pieces.

    Go home and practice throwing small objects at “very thin” glass and if you manage to break it you will likely see the catastrophic type of failure. It takes a lot of kinetic energy concentrated at a very small point (like a bullet) to not shatter the entire pane of glass.

    PS – norm is correct that it is weight and stiffness of the playing cards that matter. Of course paper (wood) is much more abrasive (shall we say harder?) than many plastics. That’s why you don’t use paper towels to clean your spectacles!

  10. Mano Singham says

    That’s why you don’t use paper towels to clean your spectacles!

    You don’t? Nobody ever told me this!

  11. Jared A says

    What have you done!

    Honestly, though, if you’re careful you’ll never notice. Especially because most modern lenses have coatings that protect against this sort of thing. But when I was a child in the early 90s I did have this problem until someone explained to me what I was doing wrong.

    Lens paper, of course, is fine.

  12. Jared A says

    Actually, on second examination I have learned that it is the stuff that is imbedded in bark that makes it abrasive. “pure” wood pulp (cellulose) is pretty soft in the grand scheme of things (cotton!). But cheap paper has all sorts of other stuff in it.

    And now I have learned something!

Leave a Reply

Your email address will not be published. Required fields are marked *