What Are Forced Oscillations and How Do They Work?

[gracy]

please i am not getting what forced oscillation really is?please explain.as far as i understand let's take example of a swing ,if we give force to it initially and leave it ,swing will oscillate all by it's own and eventually will come to rest due to damping but if we give continuous force to it ,without giving it chance to damp or stop ,then this is called forced oscillation.I know only this much about forced oscillation,please explain me the entire concept of forced oscillation.

 

[phinds]

please i am not getting what forced oscillation really is?please explain.as far as i understand let's take example of a swing ,if we give force to it initially and leave it ,swing will oscillate all by it's own and eventually will come to rest due to damping but if we give continuous force to it ,without giving it chance to damp or stop ,then this is called forced oscillation.I know only this much about forced oscillation,please explain me the entire concept of forced oscillation.

You just explained the "entire concept" yourself.

 

[A.T.]

if we give continuous force to it

What is a "continuous force"? A constant force won't work. You need a variable force:
http://en.wikipedia.org/wiki/Harmonic_oscillator#Driven_harmonic_oscillators

 

[gracy]

You just explained the "entire concept" yourself.

really.is this all about forced oscillation?

 

[phinds]

really.is this all about forced oscillation?

I don't understand your question. And your period key is stuck again.

 

[gracy]

And your period key is stuck again.

what you mean by this.i really don't understand.

 

[phinds]

what you mean by this.i really don't understand.

Well, take that "sentence" There is a period instead of a space between the word "this" and the word "I"

Your previous post had a similar period-instead-of-space.

Did you not at one point have a whole post that was full of periods and you told me it was because your period key was stuck? Are you typing periods instead of spaces on purpose? If you are, please stop. It makes your "sentences" confusing.

 

[gracy]

I don't think it was me.By the way can you please help me in my thread standing wave .please look at the last post of mine in that thread and answer if you can.It's my request.

 

[gracy]

how forced oscillation is related with resonance?

 

[phinds]

how forced oscillation is related with resonance?

Forced oscillation requires a lot of energy if you are not mating it with resonance. This is very easily understood if you look at pushing a kid on a swing. If you let the natural arc of the swing occur and then add a little at the peak, you don't have to add much at all on each swing to keep the swing going back and forth. On the other hand if you break the natural rhythm by stopping the swing before it reaches the top of its arc, or if you force it to continue beyond where it otherwise would, then in either case, your application of forced oscillation will require much more energy than if you take advantage of the natural swing.

 

[gracy]

Forced oscillation requires a lot of energy if you are not mating it with resonance. This is very easily understood if you look at pushing a kid on a swing. If you let the natural arc of the swing occur and then add a little at the peak, you don't have to add much at all on each swing to keep the swing going back and forth. On the other hand if you break the natural rhythm by stopping the swing before it reaches the top of its arc, or if you force it to continue beyond where it otherwise would, then in either case, your application of forced oscillation will require much more energy than if you take advantage of the natural swing.

what is natural frequency of the swing?

 

[phinds]

what is natural frequency of the swing?

Do you think that when you push a kid on a swing with just one push and then let go and don't push any more, that it could possibly move at anything OTHER than its natural frequency?

 

[gracy]

If you let the natural arc of the swing occur and then add a little at the peak

so are we providing new frequency( which is different than it's natural frequency) to swing?I don't think so ,i think we are giving same frequency as natural frequency of the swing,the only thing which is changing is amplitude of the swing because of resonance.right?

 

[phinds]

so are we providing new frequency( which is different than it's natural frequency) to swing?

That is not what I said.

I don't think so ,i think we are giving same frequency as natural frequency of the swing,the only thing which is changing is amplitude of the swing because of resonance.right?

yes, that IS what I said. You are simply reinforcing the amplitude of the natural frequency, otherwise it takes much more energy to do it.

 

[NascentOxygen]

so are we providing new frequency( which is different than it's natural fauency) to swing?I don't think so ,i think we are giving same frequency as natural frequency of the swing,the only thing which is changing is amplitude of the swing because of resonance.right?

Instead of synchronizing your push inputs with the natural rhythm of the swing-child system, you could grab hold of the chains with both hands and heave backwards and forwards at any fast rate of your own choosing. This is forced oscillation. Just make sure you warn the child in advance so s/he knows to hang on tight!

The novelty of the situation will likely wear off quickly.

 

[gracy]

Instead of synchronizing your push inputs with the natural rhythm of the swing-child system, you could grab hold of the chains with both hands and heave backwards and forwards at any fast rate of your own choosing. This is forced oscillation.

And if we are synchronizing our push inputs with the natural rhythm of the swing-child system i.e giving same frequency as the natural frequency of the swing ,won't it be forced oscillation?

 

[gracy]

giving same frequency as the natural frequency of the swing ,

Of course it is resonance ,so my question is resonance need forced oscillation or not?I think forced oscillation can be in both condition
(1)giving same frequency as the natural frequency of the object
(2)imparting new frequency to object
So both are included in forced oscillation but resonance is possible only in first (1)one.

 

[NascentOxygen]

And if we are synchronizing our push inputs with the natural rhythm of the swing-child system i.e giving same frequency as the natural frequency of the swing ,won't it be forced oscillation?

I wasn't sure, so referred to a few sites. It appears you are right, any periodic input is a forcing function---so results in forced oscillations.