Lets keep practing using our equations to make predictions. Lets take Newton's 2nd Law, F = ma. Lets say that you know the mass
of an object (m) and its acceleration (a) and then you calculated its Force (F), this is situation #1. Now lets say that in situation #2
the Force (F) is the same number from situation #1 but the mass of the object got twice as heavy (2m). What is the acceleration of
the object in situation #2?

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.