A simple machine has efficiency 90℅ what does it mean

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Explanation:

A simple machine has efficiency 90℅, it means that 90% of the applied force is used in doing useful work and 10% is wasted due to overcoming friction.

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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