In the simple harmonic dynamic equation, if the instantaneous value of sine is positive when t=0, its initial phase is positive angle; If the instantaneous value of sine is negative when t=0, its initial phase is negative angle.
U = um sin (Ω t+φ), where (Ω t+φ) is an angle, which is a function of time and has a certain angle with timing T. Therefore, (Ω t+φ) is the angle of alternating current at time T, which is called phase or phase angle. Different phases correspond to different instantaneous values. Generally, the initial phase, that is, the phase when t=0, is called the initial phase or initial phase angle.
Extended data:
The moving distance of an object in simple harmonic motion is four times the amplitude of the motion period and twice the amplitude of the half period, but the moving distance of a quarter period is not necessarily equal to the amplitude.
Although the distance moved by the object is equal to the amplitude when the object moves from the equilibrium position to the maximum displacement within a quarter period or from the maximum displacement to the equilibrium position within a quarter period, the distance w moved within a quarter period is equal to the amplitude when the object moves from the position between the equilibrium position and the maximum displacement. It is not equal to the amplitude.
Because the velocity of a simple harmonic moving object near the equilibrium position is greater than that near the maximum displacement, the distance from the equilibrium position to a certain position between the maximum displacement and the equilibrium position is larger. After a quarter period of the equilibrium position, the amplitude of China amplitude moves to the direction of maximum displacement. A quarter of the return journey is smaller than the amplitude.
Baidu Encyclopedia-Initial Phase Angle