NCERT Book Class 11 Physics Chapter 13 Oscillations

CHAPTER THIRTEEN

OSCILLATIONS

13.1 INTRODUCTION
In our daily life we come across various kinds of motions.
You have already learnt about some of them, e.g., rectilinear
13.1 Introduction motion and motion of a projectile. Both these motions are
13.2 Periodic and oscillatory non-repetitive. We have also learnt about uniform circular
motions motion and orbital motion of planets in the solar system. In
13.3 Simple harmonic motion these cases, the motion is repeated after a certain interval of
13.4 Simple harmonic motion time, that is, it is periodic. In your childhood, you must have
and uniform circular enjoyed rocking in a cradle or swinging on a swing. Both
motion these motions are repetitive in nature but different from the
13.5 Velocity and acceleration periodic motion of a planet. Here, the object moves to and fro
in simple harmonic motion about a mean position. The pendulum of a wall clock executes
13.6 Force law for simple a similar motion. Examples of such periodic to and fro
harmonic motion
motion abound: a boat tossing up and down in a river, the
13.7 Energy in simple harmonic
piston in a steam engine going back and forth, etc. Such a
motion
motion is termed as oscillatory motion. In this chapter we
13.8 The simple pendulum
study this motion.
Summary
The study of oscillatory motion is basic to physics; its
Points to ponder
Exercises concepts are required for the understanding of many physical
phenomena. In musical instruments, like the sitar, the guitar
or the violin, we come across vibrating strings that produce
pleasing sounds. The membranes in drums and diaphragms
in telephone and speaker systems vibrate to and fro about
their mean positions. The vibrations of air molecules make
the propagation of sound possible. In a solid, the atoms vibrate
about their equilibrium positions, the average energy of
vibrations being proportional to temperature. AC power
supply give voltage that oscillates alternately going positive
and negative about the mean value (zero).
The description of a periodic motion, in general, and
oscillatory motion, in particular, requires some fundamental
concepts, like period, frequency, displacement, amplitude
and phase. These concepts are developed in the next section.