Periodic motion : - The motion of a body that repeats itself after a regular interval of time is called periodic motion.

Vibratory motion : - If a body moves back and forth or up and down repeatedly about a fixed point is said to possess vibratory motion(oscillatory motion).

Simple pendulum : - Simple pendulum consists of a metallic body, suspended by a light inextensible string from a rigid support.

Length of the pendulum : - The length of the pendulum from the point of the suspension to the centre of the bob.

Oscillation : - The motion of a bob from one extreme position to the other and back to the first extreme position is called one oscillation.

Amplitude : - The maximum displacement of the bob from its position Side is called its amplitude.

Time-period : - The time taken to complete one oscillation is called its time-period.

Frequency : - The number of oscillation in one second is called its frequency.

Second's pendulum : - The pendulum whose time-period is 2 seconds is called a Second's pendulum.

Wave motion : - Wave motion is the disturbance which travels in a Material medium and is due to the repeated motion of the particles of a medium about their mean position, the motion being handed over from one particle to the next.

Seismic waves : - The disturbances inside the earth, which causes waves moving in all directions, are called seismic waves.

Elastic waves : - The waves, which require material medium for their transmission, are called elastic waves (or mechanical waves).

Electromagnetic waves : - Those waves, which do not require any material medium for their propagation and can travel in vacuum are called electromagnetic waves.

Transverse waves : - Transverse waves are those waves in which an individual particle of the medium move about their mean position in a direction perpendicular to the direction of wave propagation.

Longitudinal waves : - Longitudinal waves are those waves in which an individual particle of the medium move about their mean position in the same direction as the direction of wave propagation through the medium.

Pulse : - The disturbance that is sudden and lasts for short duration is called a pulse.

Progressive waves : - The transverse and longitudinal waves are mechanical waves and are called progressive waves (or travelling waves).

Simple harmonic waves : - When the vibrations of the individual particles or constituents of the medium is simple harmonic, the waves that they generate are said to be simple harmonic waves.

Amplitude of a wave : - The magnitude of maximum displacement of the vibrating particles of the medium on either side of their mean, undisturbed position is called amplitude of a wave.

Wavelength of a wave : - When a harmonic wave travels through a medium, a particular pattern repeats itself after a fixed distance called the wavelength of the wave.

Time-period : - The time taken by a crest or trough to move a distance equal to one wavelength is called the time-period.

Frequency of the wave : - Frequency of the wave is equal to the frequency of oscillation of the particles of the medium.

Wave Velocity : - The velocity of propagation of the wave is called the wave velocity.

Loudness : - The sensation produced in the ear, which enables us to distinguish between a loud, and a faint sound is called loudness.

Audible range : - The frequency between 20 hertz to 20,000 kilohertz, which are audible by a normal human ear, is called audible range.

Ultrasonic waves : - Sound with frequencies above 20 KHz are called ultrasonic waves (or ultrasound).

Infrasonic waves : - Sound with frequencies below 20 Hz are called infrasonic waves.

Supersonic speed : - When the object travels with speed greater than speed of sound, it is said to have supersonic speed.

Shock waves : - The waves produced by supersonic aircraft are known as shock waves.

Sonic boom : - The air pressure variation associated with shock wave produces a burst or cracking sound called sonic boom.

Echo : - The phenomenon of hearing back your own sound is called an echo.

Sonar : - The SONAR system is used for detecting the presence of unseen underwater objects and locating them accurately.