Oscillatory Motion

Unit - III

Oscillations, Optics and Lasers

Oscillations

Simple harmonic motion - resonance - analogy between electrical and mechanical oscillating systems – waves on a string - standing waves - traveling waves - Energy transfer of a wave – sound waves - Doppler effect.

Introduction

The vibrations or oscillations of any system constitutes one of the most important fields of study in engineering physics. Examples of such oscillations are pendulum of a clock, loaded spring and LC circuit. The knowledge about the resonant behaviour of mechanical and electrical systems is very much essential for all engineers.

Oscillatory Motion

Basic concepts 

Motion

When the position of a body (object) in the space changes with time, the body is said to be in motion.

This motion is classified into four types. They are. 

(i) Translational motion

(ii) Rotational motion

(iii) Periodic motion

(iv) Vibrational or Oscillatory motion

(i) Translational motion

If the position of a body varies linearly with time, then the motion is said to be translational motion. A car / train moving on a straight road, a ball moving on the ground are examples of translational motion.

(ii) Rotational motion

If the position of a body as a whole does not change linearly with time but it rotates at the same position about an axis, then the motion is said to be rotational motion.

The examples for rotational motion are the motion of earth about its axis, the rotation of a flywheel on its ball bearings.

(iii) Periodic motion

If a body repeats its movement at regular intervals of time, its motion is said to be periodic.

Motion of planets round the sun, rotational motion of the earth about its own axis, motion of a pendulum, oscillations of a loaded spring etc. are examples for periodic motion.

(iv) Oscillatory motion

An oscillatory motion is one in which a body moves to and fro repeatedly about a mean position,

Motion of a pendulum, oscillations of a loaded spring, to and fro motion of the prongs of tuning fork are examples for oscillatory motion.

Oscillatory motion is a special case of periodic motion in which a body vibrates to and fro about its mean position. Though all oscillatory motions are periodic, all periodic motions are not oscillatory.

Periodic Motion

A motion in which the body describes the same path in same way continuously after equal interval of time is known as the periodic motion. Simple Harmonic Motion (SHM) is a special case of periodic motion with the following characteristics.

• This is a type of periodic motion.

• The acceleration of the body is directly proportional to its displacement from a fixed point and always directed towards the fixed point.

• The restoring force developed in the body tries to bring the particle to its equilibrium position.