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

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.

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cjl
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)

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)

Andy Resnick
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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.
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...

berkeman
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.

you can learn about the principle behing this concept here:

http://en.wikipedia.org/wiki/Liquid_breathing
Space travel
Liquid immersion provides a way to reduce the physical stress of G forces. Forces applied to fluids are distributed as omnidirectional pressures. Because liquids cannot be practically compressed, they do not change density under high acceleration such as performed in aerial maneuvers or space travel. A person immersed in liquid of the same density as tissue has acceleration forces distributed around the body, rather than applied at a single point such as a seat or harness straps. This principle is used in a new type of G-suit called the Libelle G-suit, which allows aircraft pilots to remain conscious and functioning at more than 10 G acceleration by surrounding them with water in a rigid suit.
Acceleration protection by liquid immersion is limited by the differential density of body tissues and immersion fluid, limiting the utility of this method to about 15 to 20 G.[53] Extending acceleration protection beyond 20 G requires filling the lungs with fluid of density similar to water. An astronaut totally immersed in liquid, with liquid inside all body cavities, will feel little effect from extreme G forces because the forces on a liquid are distributed equally, and in all directions simultaneously. However effects will be felt because of density differences between different body tissues, so an upper acceleration limit still exists.
Liquid breathing for acceleration protection may never be practical because of the difficulty of finding a suitable breathing medium of similar density to water that is compatible with lung tissue. Perfluorocarbon fluids are twice as dense as water, hence unsuitable for this application.