X. i5ng> learning goal: understand that, for many purposes, a system can be treated as a point-like particle with its mass concentrated at the center of mass.
a complex system of objects, both point-like and extended ones, can often be treated as a point particle, located at the system's center of mass. such an approach can greatly simplify problem solving.
before you use the center of mass approach, you should first understand the following terms:

system: any collection of objects that are of interest to you in a particular situation. in many problems, you have a certain freedom in choosing your system. making a wise choice for the system is often the first step in solving the problem efficiently.

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.

amplitude

hope this