In order to reduce the reactionary force due to the momentum of the egg, the device should be built with soft materials to be effective.
A force is an agent which acts to distort the shape or change the motion of a moving object or the state of rest of a stationary object.
Momentum is the product of the mass of the a body and it's velocity.
Based in Newtons law of motion, a cushioning device for an egg can be construct such that the momentum of the egg is spread out over the surface of the cushioning material.
Therefore, the device should be built with soft materials to be effective.
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