Suppose a spring with spring constant 9 N/m is horizontal and has one end attached to a wall and the other end attached to a 2 kg mass. Suppose that the friction of the mass with the floor (i. e., the damping constant) is 1 N⋅s/m. Set up a differential equation that describes this system. Let x to denote the displacement, in meters, of the mass from its equilibrium position, and give your answer in terms of x, x′,x′′. Assume that positive displacement means the mass is farther from the wall than when the system is at equilibrium.

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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float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray