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Homework Help: I want to do an egg drop by submerging the egg in fluid. Which fluid is best?

  1. Jan 22, 2013 #1
    The basic idea is to package an egg so that it will not break when I drop it off a roof (assume 10m tall). The packaging should be as small and lightweight as possible. I know using a fluid will be rather heavy, but I'm still curious about his.

    How would I determine the optimal fluid to use? I know I would want it to move as much as possible to reduce the force on the egg's shell as it decelerates. Of course I would not want the egg to hit the walls of the container, though.

    I'm thinking I would want a fluid with an appropriate yield stress to almost match the breaking force of the shell, and then have a low viscosity so that it can decelerate significantly.

    Does this sound correct? Should I think about other stuff?

    PS: My high school sister is doing the drop. I'm just curious.
  2. jcsd
  3. Jan 22, 2013 #2


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    I've done this before, and although I don't remember the exact fluid I used, I do remember having the best results by shooting for as close to neutral buoyancy as possible.

    (Also, yield stress doesn't really have much of a meaning when it comes to fluids, since by definition, a fluid will yield under any stress)
  4. Jan 23, 2013 #3
    Also, you'll want to ensure a high enough viscosity of the liquid to ensure that the egg does not hit the bottom of your container at a high speed.

    Thus I would test a high viscosity liquid with significant buoyancy. Hence, basically your egg would only be submerged on impact, but not so much that it hits the bottom of the container (also think of the container design)
  5. Jan 23, 2013 #4

    Andy Resnick

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    Two fluids come to mind- toothpaste and cornstarch in water (try different amounts of cornstarch to fine-tune the response). I'm curious if this will work, actually...
  6. Jan 24, 2013 #5


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    Staff: Mentor

    Since this is about a schoolwork project, I've moved the thread from Classical Physics to HH/Intro Physics. We should not be doing his sister's project for her. Suggesting experiments that she can do to optimize her entry should be fine.
  7. Jan 24, 2013 #6
    you can learn about the principle behing this concept here:

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