Oscillation
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PERIODIC MOTION AND ITS CHARACTERISTICS AND TYPES OF SHM
1.1 Periodic Motion
(i) Any motion which repeats itself after regular interval of time is called periodic motion or harmonic
motion.
(ii) The constant interval of time after which the motion is repeated is called time period.
Examples : (i) Motion of planets around the sun.
(ii) Motion of the pendulum of wall clock.
1.2 Oscillatory Motion
(i) The motion of a body is said to be oscillatory or vibratory motion if it moves back and forth (to and fro)
about a fixed point after certain interval of time.
(ii) The fixed point about which the body oscillates is called mean position or equilibrium position.
Examples : (i) Vibration of the wire of 'Sitar'.
(ii) Oscillation of the mass suspended from spring.
1.3 Harmonic Functions
The trigonometric function of constant amplitude and single frequency is define as harmonic function. (Among
all the trigonometrical functions only “sin” and “cos” functions are taken as harmonic function in basic form”
Note : The function will be non-harmonic if :
(i) It’s amplitude is not constant.
(ii) It is basically formed by “tan”, “cot”, “sec”, “cosec” functions.
Some basic terms
Mean Position
The point at which the restoring force on the particle is zero and potential energy is minimum, is known as its
mean position.
Restoring Force
* The force acting on the particle which tends to bring the particle towards its mean position, is known as
restoring force.
* This force is always directed towards the mean position.
* Restoring force always acts in a direction opposite to that of displacement. Displacement is measured
from the mean position.
l It is given by F = –kx and has dimension MLT–2.
The maximum displacement of particle from mean position is define as amplitude.
Time period (T)
* The time after which the particle keeps on repeating its motion is known as time period
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