TYPES OF OSCILLATIONS:
When
the oscillator is allowed to oscillate by displacing its position from
equilibrium position, it oscillates with a frequency which is equal to the
natural frequency of the oscillator. Such an oscillation or vibration is known
as free oscillation or free vibration. In this case, the amplitude, frequency
and the energy of the vibrating object remains constant.
(i)
Vibration of a tuning fork.
(ii)
Vibration in a stretched string.
(iii)
Oscillation of a simple pendulum.
(iv)
Oscillationsof a spring-mass system.
During the oscillation of a simple pendulum (in
previous case), we have assumed that the amplitude of the oscillation is
constant and also the total energy of the oscillator is constant. But in
reality, in a medium, due to the presence of friction and air drag, the
amplitude of oscillation decreases as time progresses. It implies that the
oscillation is not sustained and the energy of the SHM decreases gradually
indicating the loss of energy. The energy lost is absorbed by the surrounding
medium. This type of oscillatory motion is known as damped oscillation. In
other words, if an oscillator moves in a resistive medium, its amplitude goes
on decreasing and the energy of the oscillator is used to do work against the
resistive medium. The motion of the oscillator is said to be damped and in this
case, the resistive force (or damping force) is proportional to the velocity of
the oscillator.
(i)
The oscillations of a pendulum (including air friction) or pendulum oscillating
inside an oil filled container.
(ii)
Electromagnetic oscillations in a tank circuit.
(iii)
Oscillations in a dead beat and ballistic galvanometers.
While playing in swing, the oscillations will stop
after a few cycles, this is due to damping. To avoid damping we have to supply
a push to sustain oscillations. By supplying energy from an external source,
the amplitude of the oscillation can be made constant. Such vibrations are
known as maintained vibrations.
The vibration of a tuning fork getting energy from a battery
or from external power supply.
Any
oscillator driven by an external periodic agency to overcome the damping is
known as forced oscillator or driven oscillator.
In
this type of vibration, the body executing vibration initially vibrates with
its natural frequency and due to the presence of external periodic force, the
body later vibrates with the frequency of the applied periodic force. Such
vibrations are known as forced vibrations.
Sound
boards of stringed instruments.
It
is a special case of forced vibrations where the frequency of external periodic
force (or driving force) matches with the natural frequency of the vibrating
body (driven). As a result the oscillating body begins to vibrate such that its
amplitude increases at each step and ultimately it has a large amplitude. Such
a phenomenon is known as resonance and the corresponding vibrations are known
as resonance vibrations.
The
breaking of glass due to sound
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