Light rays from the sun only strikes the surface of the Earth facing it, and since the Earth is not flat, but geoid, or spherical, then there will always be places backing the light rays of the sun. Now, had the Earth not been rotating about its axis, the place facing the sun would forever remain facing the sun, likewise for the other part backing it. So, there would never be night for those living on the side of Earth facing the sun, and there would never be day for those backing it.
However, since the Earth rotates, then the part facing the sun would slowly move away from it, and the part of the sun backing it would slowly move towards it, causing night time for the former, and day time to the latter.
Now, the place once backing the sun, B, is now facing the sun, and the place once facing the sun, A, is now backing it. But since the Earth continuously rotates, then B would now be slowly inching away from the sun, and A would be slowly inching towards it.
Thus, causing night at B, and day at A, and thus the circle continues, until some external force slows the Earth's rotation to a halt.
it can suddenly increase when more and more people have babies and the infant rate goes up. and how it might affect the ecosystem is the pollution that people give off.
Hearing loss due to sound energy damaging the nerve cells in the inner ear. Many animals behavior is influenced by sound energy. They learn to associate events with sounds, so they run when something crunches in the dry grass (might be a coyote), but won't be bothered by the sound of a waterfall. Mood is affected by sound energy. A wine glass can break with sound energy, if the frequency matches the resonant frequency of the wine glass and the amplitude is great enough (one Mythbusters show featured a professional singer who broke a wine glass with his voice without any amplification).