Frictional Forces: Static and Kinetic

[@AAG414]

this guy carried me through sophomore year chemistry and now he's carrying me through junior year physics

[@TravelingTreats]

Same

[@floydwynn-jones4043]

so you read Tintin books?

[@lestherviceracelocia1119]

@@floydwynn-jones4043 ii

[@lestherviceracelocia1119]

@@floydwynn-jones4043 i

[@Metamor-phosis]

@@floydwynn-jones4043 i

[@ElixiricEssence]

This is like a crash course but nothing about it is too clumped. Perfect, straight-to-the-point, and easy. Will subscribe and listen to you religiously throughout my physics course. Thank you.

[@Jai_ShriJagannath]

kzbin.info/www/bejne/enaZgqmadrRsh9k Reason of why static friction is more than kinetic or dynamic friction

[@lordofmysteries6436]

I did a short experiment. I watched this video 2 times: yesterday night and tonight. Yesterday, I understood everything he said but couldn't get anything inside my head. So I used the whole day today to read the book and solved many maths related to frictions. Tonight as I watched this video again I was able to understand everything loud and clear😁. Thanks professor Dave

[@Achievius]

Professor Dave, your videos got me through physics 1 and 2 in my post-bacc, and as I'm studying for the MCAT I found myself needing additional explanation. The jingle came to my mind and I knew exactly where to go. So thankful for you and your videos!

[@carultch]

I think of the formula for heat in terms of mass, temperature and specific heat, when I think of MCAT. Q=m*c*∆T

[@Metamor-phosis]

the jingle lol

[@alyssaboudreau3410]

Unfortunately, my prof doesn't teach anything... so I am very thankful for your videos with visual aids! I hope you keep making more!!! Yours are by far the best on youtube! :)

[@lemondrop8203]

You can't listen, that's why

[@AXbcyz]

@@lemondrop8203someone’s never experienced a bad teacher

[@andresjr.baybay2555]

thanks a lot bro. this new subscriber is from the Philippines, the way you deliver the topic is so smooth, wonderful and easy to understand. thanks a lot. static & kinetic friction topic. great!

[@AlshaipBayro]

GOOD EEVENING PROFFESOR DAVE at checking comprehension The formula Fnet=Ff+mgsin change into Fnet=mgsin-Ff 6:34 / 7:36

[@Nooneeeeeesskkr]

I had the same doubt too.

[@kera8378]

Is it sad or impressive Dave can teach in 5 minutes what my professor can’t in 3 3 hour class periods?

[@Lucky10279]

Both. Impressive for Dave but sad for your professor and you guys. I'm in the same boat with my professor. His lectures are really disorganized. I was getting a little scared that I was getting confused so early in the semester, especially when I'm way ahead of the math requirements. Watching just a few of Dave's videos and I feel much more confident. I've learned more from from short KZbin videos than from 2 hour lectures.

[@julianader739]

YESSSSSSSSSSSSSSSSSSSSS

[@blinkbubs3994]

dude thats literally what happened to me in class. 3 hour class, dont understand much. i watch this, and it makes a lot of sense.

[@Sasukej2004]

@Learn First very true, they want you to know how to do problems and smart students will read about it more at home

[@unknownbeing8222]

Am i the only kid watching this...

[@kumpulanfoto1928]

Thanks,dave. At this current time, i have a hard time learning about frictional force in orthodontic. And ur explanation makes me a little bit confidence. I understand the first 5:30 minutes,the rest remains a question for me. Thx

[@stovegamesgames6917]

I swear without this video I would be super lost in my physics class

[@SifulIslam-jo7oe]

This is my first video of yours and I subscribed as soon as I saw it at a glance 😊

[@Tony-wo6rl]

thank you so much! you saved a university newbie!

[@tridevjha255]

This Guy explained these concepts in just 8 minutes which I am Trying to understand from 2 weeks

[@lianethlozano8237]

Your videos are so helpful, thank you so much!

[@krishnanandtiwari2023]

NOW THIS IS CLEAR THANKS PROFESSOR

[@Ash_2772]

I was in tension abt tomorrow's exam but your intro made me free and calm

[@newtube553]

Lots of new ideas thank you . It's relevant in my study

[@danielgrezda3339]

1:31 "This attractive interaction can hinder motion to some degree" This can easily be taken out of context.

[@snowecaddel9454]

💀

[@ammu05]

Thank you, Professor Dave

[@henrylopez0345]

thank you man, i am teaching my nephew vectors and this video helps a lot to illustrate parts of the whole idea. thank you.

[@Jai_ShriJagannath]

kzbin.info/www/bejne/enaZgqmadrRsh9k Reason of why static friction is more than kinetic or dynamic friction

[@elfigahleitner4845]

thank you so much for sharing your knowledge with the world :D! now it all makes sense :)!!

[@meliksahyorulmazlar9742]

Thanks for helping Dave

[@iXRisesz]

Subbed not only because useful information but because Subaru 😎

[@kyle_360]

Bruh, how does this guy manage to learn something that is hard to explain in such ease and how long did it took for him to learn this stuff?

[@akila.s6856]

Wow..ur teaching is superb with practical learning

[@humaidalsuwaidi7359]

Thank you, You’ve helped me understand the difference between the frictions.

[@kipguthrie2490]

exactly what i needed before my test! thanks!

[@a4q2020]

We could see how much effort you put into creating a video. Super.👍 We A4Q team with your growth. Full support 💪

[@neurodivergentsophie8411]

Professor Dave, I have a question! If friction is caused by forces of attraction between atoms on a molecular, and electrostatic attraction is one of of these forces of attraction. Does this mean that friction can change based on the charge of the object?

[@qriosiumi2455]

Is it specified that the attraction is really electrostatic?

[@whhy9708]

Oh sir... Thanks for saving me ... Actually i love physics but the concept of cofficent "i was unable to understand 8t properly but after you video .. everythings is clear... Thanks sir! !!!!

[@carultch]

Coefficient just means a number multiplied by another number. Like in y = A*x^2 + B*x + C, the A and B are examples of coefficients.

[@BonjourMelanie]

Hello! In the comprehension check you use Fnet= mg sin theta - Ff, I am confused as to why you are using subtraction instead of addition. Thanks!

[@ProfessorDaveExplains]

it's true, it could be addition as long as you then make the frictional force negative, we just need opposite signs on the two horizontal forces as they are in opposite directions. in the end, as long as the signs make sense you're all good!

[@pubuduweerakoon7174]

There is no certain direction for a frictional force to be acted. It is always resistive to a motion or to an attempt to the motion. When the block moves or tends to move down, frictional force would act up the incline. When the block moves or tends to move up, the frictional force would act down the incline. Thanks.

[@Diamondlight04]

Is it safe to assume then, that in problems like these as long as the box is going downwards the frictional force will be negative ?

[@phamdung3884]

KB yes. It’s in the opposite direction of the motion so it’ll be negative.

[@IgnitedIce81]

Thank you so much, I was stuck on a question and this video helped me a lot!

[@Jai_ShriJagannath]

kzbin.info/www/bejne/enaZgqmadrRsh9k Reason of why static friction is more than kinetic or dynamic friction

[@magdalenakamecka1666]

i think there is an error in checking comprehension. if the object is at rest, we wont know whether it moves unless we look at the static friction coefficient (as opposed to kinetic friction as stated)

[@lovelyroseacyapat6639]

thank you i really understand friction so easy

[@dollmarya5931]

The best intro ever seen😄👍🏻

[@HARIHMS]

Professor please make a video on tension it is an important topic please make it I love your teachings

[@newtube553]

Professor Dave is my life saver . While my physics professor destroy it😆

[@suzuki12334]

How do we decide whats cos and sin at 6:00

[@newtube553]

@@suzuki12334 at my channel looke

[@suzuki12334]

@@newtube553 kzbin.info/www/bejne/inSVZKp6aJl2bc0 heres what i thought but ty

[@carultch]

@@suzuki12334 The easiest way to decide what needs to be sine and cosine, is to inspect the limiting cases. When theta = 0, the sine = 0, and the cosine = 1. Vice-versa happens, when theta = 90 degrees. With your intuition, think about what will realistically happen when the angle is zero, and when the angle is 90 degrees. If the force in question should also be zero when theta =0, then it is most likely going to be sine. If the force in question should be its full amount when theta=0, then it should be cosine. You might have a tangent instead of sine, so also check the other limit. See if it should be cosine, when theta=90 degrees, to conclusively determine that it should be sine.

[@ghrmaykibreab2178]

thank you for explaining clearly

[@nishantgamer3110]

Anyone from India 🇮🇳

[@gursahibramgarhia5587]

Me

[@kavyaloganathan5621]

Hi bro

[@Mcdrawunique]

Yo! I'm

[@rajalakshmimohanbabu145]

Hi bro

[@chandrappachandru1931]

Hi bro

[@AqibAli-hd7xp]

thank you dave my physics teacher didn't explain in this way as you explained . thank you very much

[@pubuduweerakoon7174]

Concepts are simply built...Thanks Sir..

[@revanthalexkumar7597]

Very precise

[@tujidititoogi]

highly recommended☺

[@Geogia679]

thank you so much sir, your excellent explanation helped me a lot today

[@mandeepkaur5354]

Thanks for explaining i was confused now i understand these topic it helps me to solve jee questions

[@abdullahalshadadi292]

7:05 No, THANK YOU!!!!!!!

[@rossclark6906]

Keanu reeves

[@jamiegallier2106]

Thanks Dave. ❤

[@ziadali8066]

6:30 Fnet = Ff - mg*Sin(ceta)

[@Mr3mos]

sorry, i'm confused - do we add parallel vectors or minus them from each other? Dave's equation is Fnet = Ff + mg*sin(θ)???

[@farhannaufal3697]

@@Mr3mosThe friction is minus because it's a vector quantity and remember that the friction is always opposite. If we define the mg*sin(35)'s direction as positive

[@edgarrazelm.certeza1396]

Basically dave is not wrong either you can add it but since the motion is acting in different direction the other one would act as negative and the answer will be net force going to the direction of the larger one👌👌

[@250physicst3]

What Dave did is correct. The frictional force is always opposite to the applied force that's why has negative sign and the sine component of the weight is positive because it has the same direction with the applied force

[@lovelykids9785]

Super! You made the subject simple! Thanks

[@VAISANAN373]

Thank you. It helped a lot .

[@Linhkinhbrods]

could u explain more about the process of coldwelding that also catalyze static friction?

[@evapace43]

I love you and your channel so much dude

[@hdadam203]

Thank you man, you nailed it. My teacher can’t even explain it clearly 🙄

[@hala1909]

Thank you for illustrating perfectly

[@hmpetrina5548]

Professor Dave explains ❤️❤️❤️🥰👍🏻 love this

[@kavyaloganathan5621]

Amazing explanation, clear words, but a small request. If you could explain the numericals, it would be more helpful. Thank you.

[@LaurensITrust]

You're the best

[@kazuhiramiller7752]

But Sir how we will know what is the value of cos 35° and sin 35°?

[@IamPazan]

Professor Dave Explains , The Classic Vintage Intro.

[@05afnanabdullah87]

Can work done against non conservative forces get stored in the form of potential energy?

[@ProfessorDaveExplains]

oh man, good question. i can't think of how that would work but i'm sure there must be some example.

[@05afnanabdullah87]

Professor Dave Explains​ the Induced magnetic field in a coil is a non conservative field. Still work is stored in the form of magnetic potential energy. Is it the same thing? Thanks :)

[@pubuduweerakoon7174]

Can't. That work will be wasted mostly as heat. This is what the meaning of "nonconservative"

[@pubuduweerakoon7174]

It is very clear that, any conservative force must be accompanied with a kind of potential energy. But Nonconservative forces are not. By the way, conservative force is defined by the equation of F = dU/dx. Where dU is the differential of potential energy. Work done against a conservative force will result an increase in the kind of potential energy and vise versa. Work done by a nonconservative force will definitely waste the energy which is not reversible as dU. Thank you Sir.

[@Attalla-t9b]

6:54 I wonder if the Fnet=mgcos(theta)-Fsf resulted in a negative number (meaning the Fsf is greater than the mgcos), then what will happen? Will the box stay at rest or will the box move upwards? Depending on the context though, i'd guess the box would remain at rest.

[@Homie5151]

As said in the video, any applied force less than the maximum static frictional force will cancel out resulting in no overall movement of the object even if frictional force is much larger than applied force because it is simply meant to maintain the motion of the object (or lack thereof).

[@niceguy4801]

Thankyou Professor Dave!

[@stevewalby1749]

Great explanation - thanks

[@atchayap1434]

Hey man you are the legend of science... I love that intro song..

[@emanalnashami3835]

thanks, really helped

[@AqibAli-hd7xp]

Nice explained.

[@noyes5178]

Why is coefficient of friction = the angle the object is sliding at? Isn't it determined by the surfaces smoothness?

[@Nikkizsche]

Helpful :) thank you.

[@akashbehera1465]

ya really

[@ahkthey713]

That fact that I understand friction more by watching him than by listening to my teachers lecture

[@haafilah253]

when the mass of an object increases the normal & frictional force increases do the static force increases as well?

[@maevamiranda1828]

Wow thanks alot ,it was really well explained

[@sebastianrojas5419]

This model works very well for hard surfaces. I wonder how the contact area and other factors start to be important when analyzing friction in deformable surfaces like rubber or human tissue? Would be interesting to know :)

[@TrueMose]

If you were not on KZbin I’d be having a lot more trouble with physics 😅

[@valdemars1976]

To be fair, mass is not required to solve the check comprehension problem. Net force equals Fnet = mgsin(α) - μmgcos(α) = mg(sin(α)-μcos(α)). Now a = Fnet/m therefore masses cancel out and we have final formula a = g(sin(α)-μcos(α)).

[@jordanjohn2168]

How did you get so good at solving, what did you do when you were a student... I want tipsssss as many as the s' s i put

[@kazuhiramiller7752]

I think he has used calculator. How can someone know the values of sin 35 and cos 35 and use their decimal values in an equation? The equation becomes long and we have multiply big numbers. I think giving angles like 30,45 or 60 is good because their values are easy to work with at the time of calculation.

[@remitoinfinity]

May I have a question. At 1:27 you said the interaction between atoms in the object and atoms in the surface is an attractive interaction. But shouldn't it be repulsive instead? Because the interaction here is between electrons of the object's atoms and electrons of the surface's atoms, both are negatively charged, so they should repel each other instead of attract, right? And if they repel each other, logically this interaction should help facilitate the motion by pushing the two surfaces away from each other. But in fact, motion is hindered. Could you explain how it works?

[@kazuhiramiller7752]

Atoms that are stable have no net charge. The atom consists of protons as well which cancels the effect of negatively charged electrons. In an atom (which is not an ion) the number of protons and electrons are equal and both of them have the same charge.(i.e charge in a single proton= charge in a single electron) . ( This is 100% true) But the thing is that, even if two charged bodies are interacting still friction will act upon them. Considering that the bodies are big(big enough that we can see them). This is classical physics. Here we deal with objects that are not very small. (Although I am not 100% sure about this one)

[@kaibestcarsreviewed4105]

u are really good teacher I was having a test and u saved me tnx to GOD

[@lime4328]

I LOVE U PROF. DAVE !!!

[@SamuelGebrehiwot-lx3tu]

I fucking love the intro its catchy as fuck😂😂🎉

[@akashbehera1465]

most welcome Dave

[@rhiannonlarsen5805]

Great explanations!!

[@michaelodom7023]

yes atomic is the root of the constact known as friction. its all part to understand as a whole like an ecosystem. so u can build with perfect natural law in harmony and then we can multiply this to sustain energy. but all this is to be equated in order by function amd presence naturally according to purpose relative to said application. its constant. like anything u cant have just peices and parts but as a whole .

[@abiubelo2763]

Someone can help explain where does 112.4 N comes?

[@kazuhiramiller7752]

mg sin 35° = 20 (9.8) sin 35° Here value of sin 35 is irrational. He has taken it till 4 to 5 decimal places I think which is 0.5735. So we have 20 (9.8)(0.573)= 112.4(approx) Actually the problem with this question is that how we can find the values of trigonometric ratios of angles like 35°.

[@georgemwanza7466]

Sir why are we subtracting friction forces from mgsin35 to have friction net force instead of adding to satisfy the static condition of forces in the x- axis

[@f-22raptor25]

Friction is in another direction it must be taken away

[@xboydubose7254]

What is the maximum coefficient of friction?

[@heinrichpreussen]

Metals on themselves usually have a high coefficient.

[@biggerthaninfinity7604]

What do you think the roughest surface is Professor Dave?

[@plutoniumisotope205]

Cactus

[@24week61]

HOLY SHIT you just taught 45 mins in 7 mins and I actually understood everything

[@SuperCarbohydrate]

Thank you, Prof Dave! One quick question, As you mentioned Fnet = Ff +mg sinθ But in the last example The solution is Fnet = mg sin 35° - Ff I want to know why it is negative (or you subtract Ff in stead of add) Is it because mg sin 35° and Ff is in opposite direction so that you make it negative? Thank you very much for your effort and I am looking forward to complete the whole series of 43 videos!!:D

[@maynur1]

As you know, F=MA And the block travels downwards with acceleration "a". Frictional force always opposes the motion of a surface over another surface. So as the frictional force increases, the acceleration of the block decreases. Therefore, the friction force will be negative because it affects the acceleration. And when acceleration is affected, the force will also be affected. This means Fnet = mg sin 35° - Ff.

[@SuperCarbohydrate]

@@maynur1 Thank you so much for your explanation!! Now I understand more about it!:DDD

[@helixczswks111]

thankyou so much bro

[@NewToneProducer]

FYI for people watching this, Fstatic is NOT always greater than Fkinetic. The magnitude of Fstatic depends on how much other force acting parallel to the surface exists. Fstatic can be as much as 0 N if there are no forces trying to slide the object across the surface.

[@carultch]

It is mu_static that is always greater than mu_kinetic. N*mu_static sets the upper limit for how large Fstatic can be. Whereas N*mu_kinetic sets what the friction force will be, in the event that there is existing sliding veocity.

[@MichaelBarr-h6c]

there is no static friction of the force is Zero.

[@aschetos]

Very good

[@lovelyroy2891]

Can anyone explain why add? 6:27

[@ppmp9937]

Thank you sir!

[@kai.acadventure]

Excuse me. At 6:30 is there a mistake in the formula?

[@ahmadhegazy7811]

force is a vector so it has magnitude and direction ( net force could be (negative mg sin cita) + f friction or mg sin cita - f friction )

[@vincent_______dio]

Thank you 💜

[@Rayan-jx3sn]

Thank you so much sir!!!!

[@americanmathematics5478]

I gave my life for Physics

[@DhruvMishra-k8m]

True and false - 1. The limiting force of static friction depends on area and contact and independent of material 2. The limiting force of kinetic friction depends upon area of contact and independent of material 3. The limiting force of kinetic friction is independent of area of contact and it depends on material 4. The limiting force of static friction is independent of area and contact and depends on material. 5. Both limiting friction and static friction depends on area of contact and nature of material

[@riteshbelbase8361]

Sir, how do we calculate the coefficients of friction?

[@carultch]

Given what information? Unless you are given the information that allows you to reverse these formulas and calculate the coefficients of friction, there is no way to calculate it from first principles and only the identity of the materials. This is information you look up in a reference table, in order to determine. Or you experimentally measure it yourself.

[@NAYAN-t3e]

It is either given in the problem data or we have to calculate by using all these formulas. It is actually experimentally determined & calculated value for each & every pair of materials under loading conditions. Found to be with some variations affected under temperature, surface roughness quality & many more factors. At 11th-12th & undergraduate engineering level only its available values are used. But how actually these values are came which is studied in Masters & doctorate levels with the domains of "Tribology" & "Surface Engineering" under the branches of Mechanical, Materials, Civil engineering & all.

[@dumb_lord394]

science should be learned from guys like you