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Egg Drop Experiment Real World?
I am doing the classic experiment for Physical science in which we design a "vehicle" or container to drop off of a six story building to ensure that our container protects an egg from breaking.
I have designed and tested my experiment, and I'm asking for help with one part. Does my design use the same concept as an air bag in a car?
My design is a small, sturdy box. I placed saran wrap over the box and placed the egg on top, letting it sit suspended in the center of the box in order to keep it from hitting the bottom of the box. I secured the edges of the wrap to the edges of the box, then placed and secured another sheet of saran wrap in order to keep the egg from hitting the top and sides of the box. I dropped it and tested it a few times and it worked.
So does this design mimick an air bag, or am I mistaken? As in, the air between the egg and the box absorbs the force before it reaches the egg, like an air bag between the person and the dashboard of the car absorbs the shock before the person hits the board?
Thanks (:
2 Answers
- tiggerLv 710 years agoFavorite Answer
I am not certain what 'saran wrap' is, but I assume it is flexible plastic (maybe polythene) sheet containing lots of air bubbles. If so then yes, there is a similarity in principle with a car's air bag.
But the idea that air can absorb a force is unscientific; you would do better to explain what is happening along these lines -
When the egg (and its wrapping) hit the ground, the egg must be decelerated to bring its speed to zero. This means (according to Newton's laws) that a force must be applied to the egg. To prevent the egg from breaking we must minimise this decelerating force. We must also minimise the pressure which this force exerts on the egg, since the shell is more likely to break if the decelerating force is concentrated so as to apply a large pressure over a small area.
So 2 tactics can be used -
1) Minimise the force. This can be achieved by designing for as small an acceleration as possible, since force = mass* acceleration. This in turn can be achieved if we arrange for the distance (d) traveled during the deceleration to be large since v^2 = 2*a*d, leading to acceleration (a) being inversely proportional to distance. Overall, the required force is inversely proportional to distance traveled during the deceleration phase. The soft, compressible wrapping allows for considerable deformation (compressibility) during the deceleration, and this extends the deceleration over a considerable distance, as required for minimising the force.
2) Minimise the pressure. This can be achieved by spreading the applied force over as wide an area on the surface of the egg as possible. Again, the flexible, deformable wrapping will ensure this, since if the force becomes concentrated at any point, the wrapping will readily deform, autmatically spreading the force over a wider area, and reducing the pressure.
You can see from this that the box has little function except to hold the whole thing together. You could in fact remove it, and use a poly bag as a container.
A third tactic would be to reduce the speed of descent by using a very voluminous wrapping which would have lots of air resistance and would act like a parachute. This is a very useful tactic since v^2 = 2*a*d, meaning that acceleration (and therefore force) is proportional to v^2. Halving the speed would reduce the force to a quarter, other things being equal.
