If something changes motion, are forces balanced or unbalanced?

Why do scientists believe that light is made of streams of particles? scientists believe that light is made of streams of particles because only the presence of photons can explain phenomena observed during experiments on the photoelectric effect. these observations include only some frequencies of light causing the ejection of electrons, no time gap existing between light striking a metal and electrons being ejected, and intensity having no effect on the kinetic energy of the ejected electrons.

What happens to light waves from a star as the star moves away from earth?

What determines the amount of inertia an object has