[hamdani yusuf (OP)]

I've compiled the important points to distinguish diffraction from interference in a Youtube video. It is un-shortened version from the one I posted previously to participate in #VeritasiumContest. Without time constraint, I hope it's more bearable to watch and learn from.

[Eternal Student]

Hi Hamdani.  I hope you are well.

I saw the original short video you put in the Just chat thread and made comments there.
   I will watch this longer video and comment again but the situation or the nature of this thread is getting a bit marginal now.  To state the situation directly:  If you get enough views then you get paid for that video.  This is a grey area, since a line has to be drawn to stop people advertising their own products on this forum.
   I am assuming that you are seeking some feedback and general discussion.

1.    As before, the narrator is a digitised voice and is hard to listen to.   Actually, I'd prefer to just read the information, the narrator is adding nothing, except possibly increasing accessibility for people who are partially sighted.  However, you could just spend the time to fill out the subtitles properly and then they can use their own software to read this out in a voice of their own choosing.

2.   The video is a little easier to follow and doesn't leave the viewer feeling quite as uncomfortable and panicked as before.  This is because the narrator is at least reading all the text and not just snippets of it.  This is definitely an improvement.

3.   There is no use of animation, which is OK since it's not always needed.  However, there is nothing in this video that actually required  animation or audio.   There's hardly enough time to even study the diagrams and some of them weren't required anyway.  You could have produced the same information and diagrams in a book or static web page.  As mentioned earlier, I think this would actually be better since the viewer can then set their own pace rather than be rushed along to the next section before they were ready or bored with something they already knew.  My teacher training course would have said this (the video production) was an inappropriate and inefficient use of media.

4.  The video is non-interactive and does not engage the audience at all.  We're being given a talking to by a boring voice.  A better video will slow down and ask question - possibly giving the audience a moment to think about what they might expect to see as the result of an experiment  etc.  In general, the audience should be actively engaged if you want them learn better.

5.   Overall there is a lot of improvement here over your short version.  However, you may have demonstrated that this topic cannot be presented as an interesting video in just 1 minute, you can't even fit it into 2 minutes.  If you're still going after that competition then perhaps you have to consider another topic is required and the limitation of having only 1 minute must feature heavily in your choice of topic.

6.    There are some factual errors in your information, although they are minor and probably the result of rushing the delivery of information.   For example, you said something like "interference requires waves with the same frequency".

[hamdani yusuf (OP)]

Thanks for you feed back.
I'll reply the points specifically about the competition in the other thread.

6.    There are some factual errors in your information, although they are minor and probably the result of rushing the delivery of information.   For example, you said something like "interference requires waves with the same frequency".

Can you show me interference from waves with different frequency?

[Eternal Student]

Beats.

Sound waves with almost the same frequency combine to produce a wave with a discernible amplitude modulation at fixed spatial location.

https://en.wikipedia.org/wiki/Beat_(acoustics)

You mentioned beats for 10 seconds in the video so you should know about them.

Any two sound waves (let's say travelling in opposing directions) will interfere, it doesn't matter how different their frequencies are.   It's just that we only notice stable effects easily when the frequencies are the same or very similar.

[hamdani yusuf (OP)]

Beats.

Sound waves with almost the same frequency combine to produce a wave with a discernible amplitude modulation at fixed spatial location.

https://en.wikipedia.org/wiki/Beat_(acoustics)

You mentioned beats for 10 seconds in the video so you should know about them.

Any two sound waves (let's say travelling in opposing directions) will interfere, it doesn't matter how different their frequencies are.   It's just that we only notice stable effects easily when the frequencies are the same or very similar.

I mentioned in the video that beat is a form of superposition which is not called interference. Otherwise, the names would be redundant. 

Even diffraction, reflection, and refraction are effects of superposition.  None of them are called interference by themselves.

[Eternal Student]

Hi hamdani,

   I know what you're saying but sadly these are called "interference effects" by many Physicists and we can't just change the terminology:

Examples of definitions and usage of the phrase "interference":
Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium.
   Taken from  https://www.physicsclassroom.com/class/sound/Lesson-3/Interference-and-Beats

In acoustics, a beat is an interference pattern between two sounds of slightly different frequencies, perceived as a periodic variation in volume whose rate is the difference of the two frequencies.
     Taken from  https://en.wikipedia.org/wiki/Beat_(acoustics)

  ... and many more exist...

Also, while we're here discussing the issue:  It is possible to explain diffraction around sharp edges using Huygens wavelet's Principle   -  and then it is just like interference.   See, for example   https://en.wikipedia.org/wiki/Huygens%E2%80%93Fresnel_principle.

Perhaps, if we return to the original title of your thread - people confuse diffraction and interference because they are actually all a consequence of superposition under certain assumptions and models.

[Eternal Student]

Hi again.

I think this might be a better way to phrase something:

At school level, there can be a clear distinction between diffraction and interference.   You can find references like the ones you (Hamdani) have posted already that will compare the differences.

At university level, the distinction becomes blurred.

What this means is that your video, which aims to show the two are completely different things, may be helping some people to understand initially  but  causing them problems and becoming something they need to un-learn later if they study physics at a higher level.   This isn't necessarily too much to worry about, that's what school physics teaching is often about.  Sometimes your teacher will admit that they are only showing students the simpler models and giving them definitions that are stipulated on the school examination syllabus.

[VanessaOweDa]

One thing I dont understand is that speed is defined as the absolute value of velocity,
but speed distance /time and velocity displacement / time have different terms in the numerator, havent they?

Please could someone clarify. Thanks.

[hamdani yusuf (OP)]

I know what you're saying but sadly these are called "interference effects" by many Physicists and we can't just change the terminology:

At least we can suggest or persuade them to be more consistent and stop using confusing terminology.

Perhaps, if we return to the original title of your thread - people confuse diffraction and interference because they are actually all a consequence of superposition under certain assumptions and models.

Agreed.

[Eternal Student]

One thing I dont understand is that speed is defined as the absolute value of velocity,
but speed distance /time and velocity displacement / time have different terms in the numerator, havent they?

Please could someone clarify. Thanks.

Hi Vanessa,

    You are displaying an email address or ICQ contact.  This worries me a bit.  Are you sure you want to do this?
Your question can certainly be answered but could I ask you to start a new thread for that question please.  It does not relate to the main topic in this thread unless you are suggesting that Hamdani should make this a topic for his video.  Are you suggesting Hamdani should do that?
      Why am I being a little evasive?   You're quite new here and displaying contact details.  I'm suspicious I could waste an hour of my time making replies while your primary intention was just to advertise or spam the site anyway.

[hamdani yusuf (OP)]

There's a reason why spatially resolved superposition aka interference is not commonly mentioned in the case of sound. Naturally, humans can only sense sound at two points at once, using both ears. It's in contrast with eyes with many light sensitive cells in retina, which can detect many points of light at once.
The lack of easily observed example may had motivated educators in the past to look for the closest analogy for interference of light in sound wave. They started to call beat, which is temporally resolved superposition of sound, as an example of interference too.

[TommyJ]

Confusion really comes from different formulation, demonstration examples/experiments (light, optic, sound, sea waves) and practical implementations.
Interference - is  waves superposition, resulting in altering amplitude. These may be different sources or instances of the same source reflections.
Diffraction - is banding of a wave around an obstacle or opening (a wave here is either a 'pure' single source or resulting superposed waves).

[alancalverd]

One thing I dont understand is that speed is defined as the absolute value of velocity,
but speed distance /time and velocity displacement / time have different terms in the numerator, havent they?

Please could someone clarify. Thanks.

The term "absolute value" is misleading and unhelpful.

Velocity is a vector: it has magnitude and direction
Speed is a scalar: it has magnitude only

Acceleration is the rate of change of velocity, so an object can accelerate at constant speed by changing direction.

[hamdani yusuf (OP)]

Clickbait is Unreasonably Effective

The title and thumbnail play a huge role in a video's success or failure.

Maybe I can try his advice to crank up the number of views of my video.
I have several options, such as
"Simple physics concepts many people get confused"
or a more bombastic one
"Simple physics concepts even physics professors got wrong"

I've compiled the important points to distinguish diffraction from interference in a Youtube video. It is un-shortened version from the one I posted previously to participate in #VeritasiumContest. Without time constraint, I hope it's more bearable to watch and learn from.

[emelymorris]

Diffraction is inextricably linked with the phenomenon of interference. Moreover, the very phenomenon of diffraction is often interpreted as a case of interference of waves limited in space (interference of secondary waves). A common property of all diffraction phenomena is the dependence of the degree of its manifestation on the ratio between the wavelength λ and the size of the wavefront width d, or an opaque screen in the path of its propagation, or inhomogeneities in the structure of the wave itself.

[Eternal Student]

Hi.

Diffraction is inextricably linked with the phenomenon of interference. Moreover, the very phenomenon of diffraction is often interpreted as a case of interference of waves limited in space (interference of secondary waves).

    Sounds like Huygens principle.   I think this was mentioned a long time ago - but I know it is impossible to read all the previous posts.   Anyway, emelymorris you seem fairly new here -  welcome and I hope all is well with you.

[hamdani yusuf (OP)]

Diffraction is inextricably linked with the phenomenon of interference. Moreover, the very phenomenon of diffraction is often interpreted as a case of interference of waves limited in space (interference of secondary waves). A common property of all diffraction phenomena is the dependence of the degree of its manifestation on the ratio between the wavelength λ and the size of the wavefront width d, or an opaque screen in the path of its propagation, or inhomogeneities in the structure of the wave itself.

It seems like you are one of the victims of misinformation. You can produce diffraction effect without involving interference, and vice versa. You can read this thread from the start, or just simply watch my video in post#20.

I've compiled the important points to distinguish diffraction from interference in a Youtube video. It is un-shortened version from the one I posted previously to participate in #VeritasiumContest. Without time constraint, I hope it's more bearable to watch and learn from.

[hamdani yusuf (OP)]

At university level, the distinction becomes blurred.

Why should it? 
Two distinct phenomena shouldn't be confused just because they often come together. As long as they can occur separately, the distinction should be kept clear.
On the other hand, if they always come together, and there's no way to separate them, we can say that they are synonymous.

[hamdani yusuf (OP)]

I've also made an experiment on diffraction using microwave.

My conclusion so far is that diffraction can occur if the penetration depth of the light through the obstacle is significantly more than the wavelength. In case of microwave on aluminum plate, the penetration depth is much lower than the wavelength. That's why diffraction effect can't be detected.

[alancalverd]

Very neat experiment!

What do you think is happening at 1:24?

What wavelength are you using?