The change in pitch of a train's horn as it passes while you are
standing still can be described by the Doppler effect, but that
doesn't explain it.
Answer:
At the critical angle the angle of refraction (outside the medium) is 90°
Ni sin θ = Na sin 90° = 1 assuming outside medium is air
sin θ = 1 / Ni where Ni is the refractive of the medium involved
Answer:
Digestion begins in the mouth, when you chew.
