The Physical Mechanism of Relativistic Effects and Applicable Conditions of Relativity

Relativistic effects exist in the theory of relativity,but not in Newtonian mechanics. What's leading to this distinction of the two theories? What's the relationship between this distinction and the applicable conditions of Newtonian mechanics? Does Relativity have applicable conditions? How to research the applicable conditions of relativity? What's the applicable condition of relativity? This paper discusses these issues through analysis and modeling,gets the physical causes of forming relativistic effects,and proposes three researching methods of relativistic applicable conditions. Two applicable conditions of relativity have been obtained by these methods and explain some difficult problems handed down in physics.