Physics 8.1.03a - The Inverse Square Law

[@Agirlswierdworld]

my physics teacher refused to explain this, thank you

[@நக்மாசெல்]

He studied physics for the sake of some external reasons. He cant understand the subject

[@maxim1308]

@Johnny Street Sign it destroys what certainly?

[@maxim1308]

@Johnny Street Sign respect that!

[@jokerryt2503]

@Frederic Reeber dang! Took about 1 year but it finally worked and now I am jobless I thank Instapwn for helping me so much

[@Jerryofberry]

You explained this concept quite thoroughly. Im a senior student and was trying to understand as to why it was an inverse square relationship for the force of gravity. And not just an inverse relationship. This video explained it beautifully. Thank you so much!

[@derekowens]

For gravity, it is F = (G m1 m2) / r^2. For other inverse square relationships there are different equations, but they all have a similar form, that is, they all have a variable squared in the deonominator.

[@howardburrage3874]

I wish all youtube was like this. Straight forward explanation and demonstration. In fact, I wish the whole internet or life itself was like this. We could learn so much rather than constantly digging through all the bull.

[@bobwaarjr]

Great explanation. I've been looking for something like this to use in my college photography classes to show the relationship between light distance & exposure. This is it. Bravo!

[@whyf9902]

A video with an actual clear explanation. Great video

[@cyndawu1940]

Sir, you are a saviour. A 10/10 explanation with a cookie bonus, THANKS

[@Orixx4ever]

I understood everything, loved this. God I wish I had a teacher like you !!

[@nivasraj5599]

I'm watching this 10 years later 🙃

[@derekowens]

And the concepts are still true! That's one of the things I like about physics.

[@أحمد-ف9ل6ق]

Wow you still reply even after 10 years.

[@derekowens]

@@أحمد-ف9ل6ق And I hope to still be here 10 years from now, or more.

[@nivasraj5599]

@@derekowens how old are you?

[@derekowens]

@@nivasraj5599 I was born in 1966.

[@crystinamarie1]

Thank you for this video. Taking basic Astronomy and had trouble wrapping my head around this concept!

[@utuber7781]

THANK YOU! Perfect explanation that I have wondered about since High School and I'm 40!

[@naveensundar4765]

im50

[@HeyItsKora]

I love how this is analogous to graph transformation. It creates a new way to view graph transforms

[@D4rrag00nXD]

Also known to Michael Reeves as "Light get more dim, when it more farther away" 🤣

[@noorhamdan1235]

You have a great way of explaining and it’s really entertaining 👏❤️

[@wrinkle1784]

Here after more than 14 years and will take this knowledge with me till the day my cognitive abilities leave me .

[@mbatson13]

Thank you!! I knew I could understand it but I’ve not had it explained so clearly before.

[@bludoggy71]

Thank you sir, very clear & to the point.

[@stevemt3238]

Thank you. Is the inverse square law also valid for communication/radio signals over vast distances in a vacuum? What remains of a radio signal after it traveling 240,000 miles to the moon?... or 34M miles from the earth to mars?

[@derekowens]

Yes, that's correct. The strength of the signal decreases over distance according to an inverse square law. A dish antenna can focus the signal and can compensate for that, sometimes very effectively, but if the signal is propagating from a point source, through 3 dimensional space, then the inverse square law should apply.

[@deanrose2384]

The first time I watched this I didn't realise my speakers were turned off, I just thought it was a visual only video. It was excrutiating, and a bit baffling, except that I could see the geometry at play. Made much more sense with the audio on though hahaha. Duh

[@rayo3117]

Thats creepy to imagine idk why xD a bit eerie

[@sinerntous6433]

Knowledge is awesome.

[@justderp5713]

Suprisingly simple concept for such a complex name

[@BrbWinning]

This video has given me such a better understanding of the entire concept. Thankyou very much!!!

[@Shonade_Malik]

For a video almost as old as me, this was pretty easy to understand. Thanks!!

[@Reaction1s]

1. Why did the lines of symmetry and rotation break as z increased? 2. Why did you use a rectangle which has an additional inverted symmetry with 4 rotations? 3. Why not start with a circle or triangle, which both have one symmety and infinite or zero rotations, respectively, that add complexity but are ignorable? 4. Why, at 3dz, did the expansion of 1 to 4, not go to 16? Edit: two inversions for a sheet. 0 or 1 for rotations. Edit 2: the proposed 4 symmetries for squares, should really only be two because, rotation does the remainder; I.e. a rotation for every symmetry. So, 1/8th gets closer to the third pinch point.

[@RAJEO1]

Awesome, thank you for your help. Videos like this, from people like you, are an enormous help to us students. I`m sending you a good karma payment.

[@kirkusarelius3365]

TY for the visual. For those of us that are less math inclined, how much less would a light source be for something 237,000 miles away like the moon please?

[@theresacoles7104]

11 years later and it’s still true. Thank you for making this video this makes learning physics online so much easier

[@jojojawjaw]

What a great explanation! .. you sir are awesome .. thanks.

[@josephhurdman5588]

Does the Inverse Square Law explain the Fermi Paradox? Radio waves are ballistic, too...

[@derekowens]

@Akileze Yes, Coulomb's Law is also an example of an inverse square law. The equations for electric charge have many similarities to the equations for gravity.

[@slysparkane808]

Great presentation. I have only 1 question. Would the Inverse Square law ever arrive at a 0 value. Meaning, given your illumination example, would there ever be a distance when, mathematically, the distant screen received 0 light?

[@derekowens]

Mathematically, it would never get to zero, no matter how large the distance. In practice, at some distance the force would be too small to measure and at that point would probably be considered zero for practical purposes.

[@slysparkane808]

@@derekowens thats what thought.. I just needed to hear it from someone who knows it better!! Thanks

[@davesims7917]

Based on the inverse square law wouldn’t the moon be so incredibly bright where it would be impossible to actually get anywhere remotely close to it based on what they say the distance is?

[@derekowens]

I think there are two things to consider here: The inverse square law assumes the light comes from a point source, which would be the center point. When you are far away from the moon, this assumption is valid. When you are close to the moon, it is much less like a single point. Second, the light is reflected off the surface. When you are close to the moon, you are only seeing a small portion of that surface.

[@gabeholmes1]

Man i am in sixth grade and i understood this you are a great teacher

[@dannyholley]

***** Wow, well aren't you a wet blanket...

[@SogMosee]

+Gabe Holmes how is 7th grade?

[@Agirlswierdworld]

how's 8th grade?

[@hanna630]

how is highschool?

[@stylus2006]

In a RFID system, with a reader and tag, where the distance between them is 0.04 m. how to apply this concept ? Thanks in advance for your help......

[@derekowens]

@metalupyourass9 Yes, I think you have the right idea. At 3 meters, you have 1/4 the light intensity that you have at 1.5 meters. Increasing the distance by a factor of 2 will cut the intensity to 1/4. And yes, if you start at 1 meter, then the squares you are imagining are smaller than if you start at 1.5 meters. At 3m, you will have 1/9 the light that you have at 1m, and 1/4 the light you have at 1.5m.

[@janedoe5229]

Thanks. I am reading about Newton for my own pleasure, and I am up to the point where he and Hooke argue about whether Newton plagiarizes Hookes "inverse squares" theory. Thank you for telling me what they were arguing about.

[@pipony8939]

Where do you read

[@josephhurdman5588]

Does this explain the Fermi Paradox? Other people are "out there", but their radio signals are too faint to hear by the time they reach Earth-based radio telescopes...

[@mcculloughdakota]

I understand this concept as a proportion of brightness to distance in regard to diffused reflected light but am struggling to understand how to apply it to direct reflected light since in this scenario brightness is constant. With direct reflection wouldn't it be a proportion of distance to surface area that the light fills?

[@rahuldeofitness7368]

My question is that, E=lm/m2.but. E=I(luminous insity)/m2 according to laws of illumination.please clear my doubt

[@astroroadshow]

Just a minor addition... It was Robert Hooke that mentioned to Newton about Inverse Square Law application to Gravity. Newton never gave him the credit due to a previous conflict regarding the origin of colour.

[@derekowens]

Keep trying. You can learn to like it. Kind of like coffee.

[@naveensundar4765]

May I know to which comment are you responding this to ?

[@aquaexnar3093]

@@naveensundar4765 necroooooooo

[@gonzilo436]

@@aquaexnar3093 not really a thing in yt

[@aquaexnar3093]

@@gonzilo436 bro a necro is a necro, no matter where it is. dont respond to a 7 year old post

[@Hippo464]

How does this work in space?

[@fcrick6967]

what about laser beams which are minimally divergent or parallel rays? ...just a thought

[@seanappletree2570]

Q..... so please explain how we are meant to understand what happens say at 3m squared (9 squared meters) not sure which way round to say that? but how are those 9 squares meant to be distributed around an X and Y since potential mangetic and or electric has these values as it occupies 3D space.... cheers buddy

[@fandangofandango2022]

Very Good Teacher.

[@seanappletree2570]

I mean to say if I have a torch and point it at say grease proof paper at 3 mtrs away I will still get RADIATION expessing itself in a cone so a circle on the paper and HOW do we understand the formula for this....or is it squaring the circle?????

[@srjcdistanceeducation1799]

We want to use this video for a college course in Radiologic Technology. Please turn on Community Contributions so that we can improve the auto-generated closed captions. If you prefer not to turn on Community Contributions, please give us permission to fix the captions using the Amara.org site which will embed your video from here.

[@ChurchPreaches]

I understand that the inverse square law says if you double the distance between the light source and the screen, the screen receives a quarter of the the light, how does cutting the distance in half between the light source and the screen make the screen receive only double the light? Going from 1 to 2 meters, the screen receives a quarter of the light it received from 1 meter, But if you were to go 2 to 1, the screen receives only double the light that it had from 2 meters? The math in my head doesn't make sense, I don't know where I'm going wrong. Does anyone know where I'm going wrong?

[@Akileze]

@derekowens Do you do any work/research in the area of Particle Physics? There's some data from Cern and Gran Sasso claiming they have clocked neutrinos traveling faster than light. This is a remarkable claim considering the difference is in the realm of 10^-9 on a result expected in the order of 10^-3. Nanoseconds of difference on a millisecond result is noise in my mind. Sorry to wander off topic but it's loosely related .. I think ;-) Thanks Again!

[@presbarkeep]

awesome... good job, good video. easy to understand. do sound waves follow the inverse square law too?

[@ketilsin]

The sum of the light hitting the 3x3 screen will be the same as the sum of the light hitting the original 1x1 screen. This must mean that each square in the 3x3 screen gets only 1/9th of the light. Since each small square will be less bright the whole screen must appear less bright.

[@wiccanXexodus]

@bomberfun1 you would have to take into account that light is absorbed and reflected off the air particles.

[@voidc4]

I’m a little lost. Do you find the theoretical number of squares based off of distance squared?

[@derekowens]

Yes, exactly. Multiplying the distance by x will multiply the area by x².

[@SumitPrasaduniverse]

Excellent explanation 👌

[@PoweredMinecart]

Please tell me if i'm correct or not, but the equation would be... Area Units = Units of Length Away^2

[@shesthedevilsgod6793]

So the light would at some point become invisible to the naked eye but would never petter out and go on forever? So essentially in space time nothing ever really dies. It just becomes invisible or inaudible. Therefor our actions go on forever. If you were to able to move into the 5th dimension you would be a able to experience not only the event of the light going out into space but also all possible events of the light going out into space. If you were in the 4th dimension you would be able to see the light at every point in space/time simultaneously as one event. InnerSteller was a great physics lession for us non academics

[@derekowens]

Yes, I believe they do. Anything that propagates in three dimensions should follow an inverse square law.

[@arpeggio8061]

As absurd as it sounds. Could another analogy be if a flashlight were to be powering the "light" with the Sun's UV ray somehow. Meaning that basically the flashlight contains the actual Sun. The distance of it after expanding towards the screens could be thought as Solar panels. As the closest one would most likely get the most energy and as it extends the energy decreases?

[@sahajshukla]

i just wanted to know the inverse square law applicable for gravity u r a born teacher thanxxx for helping me out

[@highgatehandyman6479]

Excellent video

[@wideasspenguin2032]

My class have to watch this video because our teacher can't explain it because of CORONA VIRUS

[@jensen6647]

yeet

[@wideasspenguin2032]

@@jensen6647 😂

[@jamhopsey]

Light get more dim when more farther away

[@pipony8939]

Don't understand it, how is the light gets more dim if it's supposed to light

[@EvanLoper-tl9qj]

Does this apply to space? And light with distances so massive.

[@derekowens]

Yes, it certainly does. You can think about the amount of light per square meter landing on earth and compare that the light per square meter landing on Mars, farther away. And on out to the more distant planets and beyond.

[@jinxelectric]

Hey Mr. Owens, how do you see that the screen at 2 meters away is 4 of the smaller screens?

[@derekowens]

At two meters away, the screen is twice as wide as it is at one meter, and also twice as tall. So the area is doubled, and then doubled again. We have to take both the width and the height into account.

[@jinxelectric]

How do you understand that the screen is twice as wide and twice as tall. I don’t see it.

[@derekowens]

@@jinxelectric It is because the light rays spread out in straight lines. If you double the distance, the light rays are then twice as far apart. And that applies to both the width and the height.

[@galacticalliance4801]

oh man thank you, this explanation is amazing.

[@Zakariah1971]

Excellent explanation. Teach me calculus.

[@samuelhong4272]

how does this relate to coulombs constant?

[@nouvchanrothana6492]

Thank you very much for your explanation.

[@Akileze]

@derekowens Thank you for your time sir and good sailing/safe passage!

[@doctari1061]

Good explanation

[@nimam7986]

Thank you for the demonstration.

[@derekowens]

@Akileze I don't work in this area, although it is certainly fascinating. I mainly teach physics and math. I've heard some chatter about these ideas lately. I don't know enough to comment on it intelligently, but it is certainly very interesting.

[@zaidhussam2546]

will take the same amount of photon atoms in each screen 1,2,3 ?>

[@ParodyUnboxings]

+Zaid Hussam whats a photon atom?

[@deanrose2384]

+ParodyUnboxings A wave-particulate of light.

[@enisten]

+Dean Rose Full of dumbs here?

[@jordanhendryx8775]

A photon is not a particle. A photon is a wave packet.

[@daysilopez7797]

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[@eweisblue]

Why not Electromagnetic force ?

[@hkdoms]

Ok so I’m struggling with this thinking about how we’re able to see stars. It doesn’t make sense to me

[@halasimov1362]

why is it that the first increment to the 2nd becomes double the width, but to the third it is just 50% wider? so why is it not 16 cubes at 3 meters?

[@derekowens]

I'll try to explain. Each individual light ray is perfectly straight. So as they spread out, their distance increases at a steady rate. So the width isn't doubling each time (1, 2, 4, 8) but instead the width is regularly increasing (1, 2, 3, 4). The inverse *square* part occurs because both the width and the height are increasing in this linear fashion: 1, 2, 3, 4, .... And since the area is the width times the height, the area increases like this: 1², 2², 3², 4². So the area increases according to the square of the distance. Hope that helps.

[@hairulbariahbaariah4203]

Thanks i understood

[@tomr1961]

What is the mathmatical equation?

[@misskikixxxx]

This was great thank you :) explained things very nicely

[@safin3389]

Thanks for the lesson

[@zone47]

Awesome, it totally makes sense! Thanks.

[@ikakhmaladze200]

nice, simple, interesting truly a great job

[@ZAGGNUT1]

Yeah, but what is a flashlight?

[@usd25674]

Good explanation of light, just know gravity has never been proven.

[@sinerntous4665]

Mathematically equated F=GMm/d2 Cipher. DECIPHER F, FORCE G,GRAVITY MM,TWO MASSES D2,DISTANCE. DECODE F,FREE G,GOD MM,MASON D2,DEVIL. UNIVERSE LAW

[@fireonstars847]

Watching this during pandemic

[@stephendean2896]

Great job this video helped me a lot

[@நக்மாசெல்]

Everytime I see an equation inversely proportional to r.square. I used to wonder what made them to assume this logic?. Why not cube?... Now only I understand.

[@naveensundar4765]

nice!

[@pavipavisumai5337]

Thank you so much sir..

[@arbaaz1816]

can u explain the kinetic theory of gases like this video

[@nathanduvergier7589]

Kinetic molecular theory is chemistry.

[@natbienvenue310]

Not sure a laser follows the same law. It doesnt spread, or spreads very little

[@captsavage3049]

Thank you. Astronomy homework solved!

[@mscovers8789]

🙏🙏

[@dannymunoz8027]

Thanks for the refresher

[@wattheshet]

Huh no math required awesome. Finally understand this inversed square law. Really hate mathematicians naming convention. Makes it more complicated/.

[@avinavinash421]

So this is how radar system works.🥳🥳🥳 I mean to reveal the position of object precisely only possible if we program computer with this equation. am I right if not correct me I am gladly open for truth.

[@fihannijer1520]

Great video

[@melaniemartinez6805]

Thank you!!

[@TheGamingWattsit]

Surely the light would create a circle?

[@derekowens]

Yes, it typically would. We're just considering a rectangular shaped screen for the light to land on. A calculation involving circles still gives the same result, though, because the area of a circle is related to the *square* of the radius. It's an inverse square law either way.

[@TheGamingWattsit]

Derek Owens could you explain this to me?

[@derekowens]

@@TheGamingWattsit As you get farther away, the circle of light would get larger. For example, if you triple the distance, the radius of the circle would triple. Since the area of the circle is Pi time the radius *squared*, the area would increase by a factor of 9, because 3 squared is 9. This means that the light is spread out over 9 times as much area, so it is only one ninth as bright.

[@TheGamingWattsit]

Derek Owens ahh ok thank you!

[@TheGamingWattsit]

Does this mean if a light source shines on a wall 1m away, the intensity of the light on the wall is equal to the power of the light divided by pi?

[@richtaylor6039]

Thank you

[@MrDieg999]

So 1/distance ^ 2

[@baden300]

thanks, really helped.