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Protecting an egg from impact

  1. Apr 14, 2012 #1
    I am given a milk carton (the small kind you drink in schools), and need to protect an egg by adding what ever I can inside the milk carton (nothing can be outside it).

    my teacher will first:

    1) Drop it from the ceiling (9ft, 2.7 meters)
    2) Drop a 16lb (7kg) bowling ball on it from a height of about a meter
    3) Sling it a wall (really really fast)
    4....) Keep slinging it at a wall (for extra credit) until the egg breaks

    What do you think is the best way to make the egg unbreakable? I plan on buying some metal from Home Depot and welding it into a frame that'll fit snugly into the box. After that, I plan on surrounding the egg in something really soft (like cotton balls, possibly shaving cream?). On the layer around that, I'll put something a bit harder, like bubble wrap. Around that, I'll put like crumpled paper. Does this sound good? Also, do you think the weight of the metal frame matters? I think it should be lighter because a heavier frame means more kinetic energy, which is going to be transferred into the egg when it impacts the floor/wall (not the bowling ball, obviously).

    Any suggestions, ideas?
     
  2. jcsd
  3. Apr 15, 2012 #2

    haruspex

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    I'm not familiar with the cartons in question, but I assume they're roughly cubic.

    The internal metal frame sounds good for the bowling ball test.
    For all the other tests, it's the mass of the egg that's the problem. Doesn't matter what the container weighs.

    In general, shocks are absorbed best by materials that crumple or break. (Motorcycle helmets are designed to crack on impact, and should then be thrown away.) That's fine for the first test, but then it's not likely to survive the rest.

    Really soft materials are not a good idea. They'll collapse a long way before they exert much restraining force, then all of the egg's momentum has to absorbed in the last microsecond, putting huge forces on the egg.
    Ideally, you want a constant force throughout the deceleration, so crumpling paper is ok. On the other hand, it needs to survive multiple tests, which suggests something more springlike. Paper might not spring back into shape well.
     
  4. Apr 15, 2012 #3
  5. Apr 15, 2012 #4
    maybe put some clay in it, or some little foam beads
     
  6. Apr 15, 2012 #5
    Might as well boil it then.
    I'd use sponges but that's just gut feel.
     
  7. Apr 15, 2012 #6

    mfb

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    The first test will stop the egg within a few cm (5?) after a height of 270cm, which requires a deceleration of approximately ~50g on average. While it might be possible that the egg survives it, the material should provide that 50g over the full 5cm and not 0g over 4cm and 250g over 1cm.
    So I think you should look for some material which is quite hard. Surround the egg carefully with this material to cover the full surface of it.
    Add something really hard around it to survive the second test.

    Oh, and then there is the "cheat" to fully cover it with some material which just does not break. Make an egg-shaped object of solid metal* with the egg inside :D, surround it with rubber.

    *something easy to melt like solder.
     
  8. Apr 15, 2012 #7
    As hqjb said, should I try using sponges? They have a lot of air pockets, so they will crumple, right? Plus, they'll spring back into shape easily, which lets the egg survive more tests.
    Do you think I should try layering the egg with different materials, like from softer to harder materials, or should I just choose one and only use that?


    I can't boil the egg or try to make it softer.

    Those numbers don't make sense to me :( , we haven't learned anything like that yet. Do you think surrounding the egg in metal is a good idea? If there's even a little space between the egg and metal, the egg will bounce around and most likely break, right? Plus, I have to take the egg out of the container after each test to show him it's not broken, and IDK how to do that when it's surrounded in metal... unless I put like hinges on it..
     
  9. Apr 15, 2012 #8

    mfb

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    Oh, you could try this: Put the egg in water. Make sure that the egg keeps some distance to the container at all times (a sponge might help here - fill it completely with water). Surround it with some container which can survive the tests.
    Try to get water in the air cell or use a fresh egg (optional).

    As the egg has approximately the density of water, this should absorb the shock quite good.
    This is an improved version of the metallic shell.
     
  10. Apr 15, 2012 #9
    That's an awesome idea, but I'm not sure how I can make a frame that can open up after each test, without having small gaps that lets water out. It wouldn't be good if my teacher slings it at the wall, only to have the entire thing explode and shower the computers near it with water... lol
     
  11. Apr 15, 2012 #10

    haruspex

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    A mix of resistances in series is a bad idea. As I said, the ideal is for the force on the egg to be constant throughout the impact period.

    I really like mfb's wet sponge idea. Imagine the egg dropped into water. The greatest force is immediate, falling off with time. This is the opposite to the pattern of resistance from the sponge, so with the right sponge/water ratio you could get a very good result.
    The other thing the sponge contributes is to return the egg to the centre of the water after each test.
    Of course, you'll need a watertight membrane around it that won't burst on impact.
     
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