# What is vibration?

hello friends,
I read this on various books and even on google that "Any motion which repeats itself after an interval of time is known as vibration". this simple line explains a lot about vibration. But i have few questions in my mind-
1. Is the rotation of wheel a vibration?
2. if rotation of wheel is not vibration then what about the small particle on the wheel, is that particle vibrating?
3. Is the beat of heart is vibration?
4. Is the movement of piston inside the cylinder is vibration?
5. is the movement of leg or hand of a normal walking person is vibration?

## Replies

• zaveri
Anku2993
"Any motion which repeats itself after an interval of time is known as vibration".

I think this definition is not entirely correct.

the examples 1 to 5 are not the examples of vibration.

one example of vibration would be the motion of the guitar string on excitation. And this is quite different from the cases 1 to 5.

now consider this example: take a rotating fan. If its blades are dynamically balanced, then the fan will rotate normally. but if any one of the blades is broken or bent, then the fan starts wobbling. this wobbling is what is called vibration.
• Ankush Sharma
zaveri
I think this definition is not entirely correct.
ok dear thanks for explaining but then according to you what is the definition of vibration?
and if according to you , the motion of the string of guitar is vibration then it means the cases from 3 to 5 mentioned in my post above are also vibrations. Think upon it once more... waiting.
• Ankita Katdare
The definition of Vibration as I know it is -

moving or causing to move continuously and rapidly to and fro.
Is this incorrect?
• Anand Tamariya
Only if the body continues the periodic motion after intial input is removed (like plucking a string), the motion is considered vibration. Else, it's just periodic motion.
• Ankush Sharma
Anand Tamariya
Only if the body continues the periodic motion after intial input is removed (like plucking a string), the motion is considered vibration. Else, it's just periodic motion.
dear the example shared by you is of free vibration. But there are also forced vibrations in which there is continuous external force acting on body. So what about it?
• Ankush Sharma
Ankita Katdare
The definition of Vibration as I know it is -
if to fro motion is considered vibration then it means the examples 3 to 5 are vibrations. isn't it?
• Anand Tamariya
Anku2993
dear the example shared by you is of free vibration. But there are also forced vibrations in which there is continuous external force acting on body. So what about it?
What's your example of forced vibration?
• Blv NAGABABU
vibration is once force applied and released then it moves only from mean position to away and towards of equal amplitude. ex:a swinging bed, etc., I think heart is an example for that
• Ankush Sharma
Anand Tamariya
What's your example of forced vibration?
dear the simple result of forced vibration is resonance.
Now examples
1. Stringing a guitar- consider that you pluck the string of guitar only once, then the vibration with which string vibrates is free vibration but if keep on plucking the string after releasing it then it is forced vibration. And if the frequency of plucking the string will equal to the natural frequency of string then it becomes resonance.

2. Pounding a drum- Similarly as above, consider that you strike the drum only once, then the vibration with which the membrane of drum vibrates is free vibration but if keep on striking the membrane after releasing force then it is forced vibration. And if the frequency of striking the membrane will equal to the natural frequency of membrane then it becomes resonance.

i hope these are simple examples to understand forced vibrations..
• Ankush Sharma
Blvn Lakshman
vibration is once force applied and released then it moves only from mean position to away and towards of equal amplitude. ex:a swinging bed, etc., I think heart is an example for that
dear again the definition provided by you is of only free vibration. if you consider forced vibration then i think 4 and 5 example is also vibration..
• zaveri
In engineering, one such example for forced vibration would be, the vibration of the automobile chassis frame, due to the vibrations of the engine
• Blv NAGABABU
thinking about 5th example the distance (amplitude) of the leg is not equal u can check 1ce. the front distance covered by the leg is less than the back distance (amplitude) so according to u its not an example for vibration.
• Blv NAGABABU
coming to ur 4th example the piston is fixed by two ends I.e., connecting rod to crank and then from crank to crank shaft. but vibration is only about one fixed point and piston is connected to the crank which the position is continously changing.
• Ankush Sharma
Blvn Lakshman
coming to ur 4th example the piston is fixed by two ends I.e., connecting rod to crank and then from crank to crank shaft.
dear it means it is not only forced vibration but forced relative vibration. Right.
• Anand Tamariya
Anku2993
dear the simple result of forced vibration is resonance.
Now examples
1. Stringing a guitar- consider that you pluck the string of guitar only once, then the vibration with which string vibrates is free vibration but if keep on plucking the string after releasing it then it is forced vibration. And if the frequency of plucking the string will equal to the natural frequency of string then it becomes resonance.

2. Pounding a drum- Similarly as above, consider that you strike the drum only once, then the vibration with which the membrane of drum vibrates is free vibration but if keep on striking the membrane after releasing force then it is forced vibration. And if the frequency of striking the membrane will equal to the natural frequency of membrane then it becomes resonance.

i hope these are simple examples to understand forced vibrations..
The two examples above are due to formation of standing waves. If you have loosened string in guitar or skin on drum, it won't really vibrate, will it?
• manojCC
Anku2993
hello friends,
I read this on various books and even on google that "Any motion which repeats itself after an interval of time is known as vibration". this simple line explains a lot about vibration. But i have few questions in my mind-
1. Is the rotation of wheel a vibration?
2. if rotation of wheel is not vibration then what about the small particle on the wheel, is that particle vibrating?
3. Is the beat of heart is vibration?
4. Is the movement of piston inside the cylinder is vibration?
5. is the movement of leg or hand of a normal walking person is vibration?

I think vibration is to and fro motion of an object or body and vibration can be defined as some form of disturbance.....
• Sekocan
Vibration must happen as oscillation, like a sine wave. It must be around some origin and if the external forces are removed (and after some dampening, resistance, loss of energy...) it must stabilize itself on that origin.
It can be periodic (like the guitar string and most of the natural frequency vibrations) and it can be random (like a car on a gravel road).

I don't know if there is a difference between vibration and oscillation. But I know that vibration is a subgroup of oscillation.

Wikipadia says this: " The term Vibration is sometimes used more narrowly to mean a mechanical oscillation but is sometimes used as a synonym of "oscillation". Oscillations occur not only in mechanical systems but also in Dynamic System in virtually every area of science: for example the beating Human Heart, Business Cycle in Economics, Predator Prey population cycles in Ecology, geothermal Geyser in Geology, vibrating strings in Musical Instrument, periodic firing of Nerve Cell in the brain, and the periodic swelling of Cepheid Variable stars in Astronomy."

I believe if you want to call an oscillation "vibration", it should have a relatively high frequency like a guitar string (not like a celestial motion).

In Turkey, if a mechanical engineer sees a machine starting to vibrate in one of its natural frequencies, he/she says: (direct translation) "It entered oscillation (phase)"

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