Physics
What are the damped vibrations? How do they differ from free vibrations? Give one example of each.
Answer
The periodic vibrations of a body of decreasing amplitude in presence of a resistive force are called the damped vibration.
In the case of damped vibrations, the amplitude of vibrations gradually decreases with time and ultimately it ceases whereas in the case of free vibrations the amplitude of vibrations remains constant and it continues forever.
Example of damped vibration — A tuning fork when stroked on a rubber pad, executes the damped vibrations in air.
Example of free vibration — The vibrations of a constant amplitude can only occur in vacuum. Since, in practice, it is very difficult to have vacuum. Hence, it is very difficult to realise such vibrations in practice.
Related Questions
Draw a sketch showing the displacement against time for a body executing the damped vibrations.
Explain why strings of different thickness are provided on stringed instrument.
[Hint — Natural frequency of vibration of a stretched string is inversely proportional to the radius (or thickness) of string so notes of different frequencies can be obtained by producing vibrations in the different strings]
The diagram given below shows three ways in which the string of length l in an instrument can vibrate.
(a) Which of the diagram shows the principal note ?
(b) Which vibration has the frequency four times that of the first ?
(c) Which vibration is of longest wavelength ?
(d) What is the ratio of the frequency of vibrations in diagrams (i) and (ii) ?
The diagram in figure below shows the displacement-time graph of a vibrating body.
(i) Name the kind of vibrations.
(ii) Give one example of such vibration.
(iii) Why is the amplitude of vibrations gradually decreasing?
(iv) What happens to the vibrations of the body after some time?