Introductory Kinetic Friction on an Incline Problem

[@LSPig]

Physics is the most confusing thing on the planet, thanks for the help!

[@FlippingPhysics]

Sorry it's so confusing. I am doing my best to unconfuse you!

[@lennyadams8275]

This video is BRILLIANT!!! I truly enjoy the way that the instructor played four different versions of himself. Better yet--the delivery of the concepts here is superb! Thank you very much for creating such a helpful video, Flipping Physics! :-)

[@FlippingPhysics]

Wow! What a lovely comment. Thanks for the high praise. 👍

[@ingmanuelleal]

Everybody brought mass !!! Excelent video. Greetings from México

[@FlippingPhysics]

Thanks for the greetings. Glad you enjoyed the video!

[@emilianorodriguez4492]

Q tranza banda😂

[@enderflair1222]

Yes! I'm so glad that this helped me. Thanks for making this! I've thrown in the deep end when I was required to find max static friction and kinetic friction for a h/w report

[@FlippingPhysics]

I am glad to have been able to help you with your report. Hope you learned something!

[@FlippingPhysics]

Any chance you could help me out by doing what I ask people to do in this video? bit.ly/2y4tOCA It would be a great way to show your appreciation!

[@farina8121]

At first, I watched this because I was doing my lab report but then I start enjoying your videos. Thanks! Haha!

[@FlippingPhysics]

That is awesome!

[@4gr8ness12]

Laughed hard and learned at the same time. Awesome video!

[@FlippingPhysics]

I don't think I could hope for more. Thanks!

[@aasdasdsad9776]

Even after 7 years, these videos are still incredibly helpful, thanks so much for these quality content - Physics can get quite challenging when we go to Tension and Newton's laws of motion.

[@ahmadkarim1144]

i love you man, i was wondering why my equation was not working but i realized i had my a backwards like your explanation

[@hasanpatel904]

Ur style of teaching is so good

[@FlippingPhysics]

Thank you!

[@dustinsmith8341]

Your videos are awesome! Way funner/easier to watch than others where its all pen and paper. Keep it up man! I still have another semester to go!

[@FlippingPhysics]

Currently keeping it up. Just posted another video today! Thanks for the compliments.

[@janejove6995]

I used this example for my class report and my teacher corrected me that the summation of forces in perpendicular direction must be the net force rather. And after my report, I realized that this problem is a little harder because the mass is not given! I think I got my classmates all confused because of the missing mass. Anyway, thank you!!

[@rain_sq]

How do people understand this? Im so confused they go way to fast and skip details that confuses me.. I appreciate the speed and edits but its hard to understand

[@xyliahvortex661]

Watch his video on breaking down the components of gravity

[@jakemogan8628]

Very engaging and to the point video to explain physics, nicely done. I have one question though, why is the acceleration negative? Is it because the book is sliding to the left, which is a negative direction? If this is the case, I don't understand how the coefficient of kinetic friction would change because it is just a matter of perspective on a 3D plane. So basically, why is acceleration negative? Thanks again.

[@FlippingPhysics]

The acceleration is negative because the object is speeding up in a negative direction. This should help: kzbin.info/www/bejne/g5ibf6Z-pcZ3qLsm49s

[@jakemogan8628]

Awesome. Thanks so much!

[@hoanglonglo2900]

I have a question. Is it the last video you said it starts to move at 15 degrees and now it is moving at only 14 degrees? I am writing my report and my measure gives me the same problems. I don't understand why a smaller angle makes the book move which creates the kinetic coefficient. if anyone knows please help.

[@prathamhebbar5800]

For the sum of the forces acting in the horizontal, could you do Fg,x - Ff,k = max? I did it that way and got a friction coefficient of 0.21. Is this wrong? Please let me know. Thank you!

[@marcylatimore7548]

i have a lab tomorrow and we have to write our own procedures and this was mad helpful

[@FlippingPhysics]

I hope it went well!

[@vikramjoshi2177]

There is another way to isolate for the coefficient of kinetic friction, where you would be left with uk = tan(theta) - (a)/gcos(theta)

[@methlokaijuthekaijuexpert]

Great video although I do have a question: wouldn’t the sum of the forces in the perpendicular direction be Fg - Ff since the force of friction is acting against the motion? Thank you!

[@FlippingPhysics]

Nope. The positives and negatives there simply have to do with the direction which the person doing the problem defines as positive. Notice in this video www.flippingphysics.com/static-friction-incline.html I put the incline going the other way and reversed the positive direction along the incline.

[@swophonorious4127]

Thanks, Mr. P. This is much clearer now!

[@tutstorial8474]

what's that app? that u use on your phone to get the angle of inclination??

[@FlippingPhysics]

It is an iOS app called "Measures".

[@mr.grapefruit3624]

Thank you, this helped me on physics homework so much!

[@HamzahAlHashemi]

Guys just BIG FAT THANKS to you, I've vainly tried to understand how to measure the static and kinetic friction coefficient, but you have fairly explained it. Can I ask that refer to the static video, it shows the angle was 15 degrees, and here it is 14 degrees, why it's reduced? Is it a statistical error only, the book or ramp is different than the previous example, or something else? Thanks you once again

[@FlippingPhysics]

You are certainly welcome. It is the same book and ramp. I believe Billy alludes to the answer to that question at 5:52 when he states that the coefficient of kinetic friction should be less than the coefficient of static friction. It is because the coefficient of kinetic friction is less than the coefficient of static friction that the incline angle is smaller.

[@HamzahAlHashemi]

Flipping Physics Thanks for your prompt response. I honestly not understand it very well, I thought the kinetic coefficient is smaller because of the negative acceleration only. I'm wondering that l, if it's the same book and ramp, how it moves here at 14 degrees, while in the previous vedio it starts to move at 15 degrees? Sorry bothering you 😊

[@FlippingPhysics]

No worries. I'll try again. 1) I would suggest you watch this video about the coefficient of friction. www.flippingphysics.com/mu-intro.html 2) It is subtle, however, notice the slight turning of the book on the way down the incline. This is caused by me at the very start when I let go of the book. I give it a very slight turn to make sure the book is moving relative to the ramp to make sure it is kinetic friction, not static. Hope that helps!

[@HamzahAlHashemi]

Flipping Physics Indeed thanks a lot. I can use the same concept for granular soil particles, ya? I'm actually conducting a research to compare the results of Angle of Repose of granular dry sand obtained from hollow cylinder test with DEM simulation result, so the DEM Simulation requires the friction coefficient as an input. I'm really grateful for your clarifications.

[@FlippingPhysics]

Good luck. Sounds interesting.

[@tiffanyminer5084]

Yall are saying this confusing but my textbook explains it as "Once the block starts to move at theta > or = theta c, it accelerates down the incline and the force of friction is fk = uk n If theta is reduced to a value less than theta c, however, it may be possible to find an angle (theta)' c such that the block moves down the incline with constant speed as a particle in equilibrium again (ax = 0). In this case, use Equations (1) and (2) with fs replaced by fk to find uk: uk = tan (theta c)' , where (theta c)' < theta c." Its not even English, so thank you for those who only have shit textbooks to learn from

[@alaaali7347]

Hi

[@phantom_drone]

How do I practice this?

[@Aer01614]

Nicely done I enjoyed your teaching method, thank you !

[@isaacmcauley6616]

Can someone explain to me why he made the displacement negative when he corrected a mistake?

[@WolfganGt3]

Thanks for the flipping help maannnn!

[@1qpfc]

Something that is confusing me... in the static friction incline example, you said the book does not slide until an angle of >15 degrees is reached. Now we are saying the book is sliding at an angle of 14 degrees, how can this be?

[@FlippingPhysics]

This is because the coefficient of kinetic friction is less than the coefficient of static friction.

[@1qpfc]

@@FlippingPhysics Okay, but how does the book slide at 14 degrees if previously it didn't slide until it reached 15 degrees? The book is starting from rest in both examples?

[@FlippingPhysics]

I give the book a very slight turn as I let go of it so the friction will be kinetic and not static.

[@ryan-ik3rq]

two words: Awesome. Video.

[@FlippingPhysics]

Thanks!

[@abeleshetu4715]

how come acceleration isn't negative when were solving for the coefficient of kinetic friction?

[@sue_yang]

why the distance is zero here?

[@weichen9720]

Then if its the acceleration is moving to the right side then the acceleration is positive but my static friction i got will be less than my kinetic friction

[@ya2ze3]

Thank you that was very helpful💙 ,but can i ask you about the app you used in iphone to determine the angel (14)?,greeting from saudi arabia✋

[@FlippingPhysics]

Glad you found the video helpful. The app is the "Compass" iOS app. If you swipe to the right when you see the compass, you get an inclinometer.

[@Roadrin]

Super helpful and easy to understand. Thank you so much.

[@FlippingPhysics]

You are welcome!

[@akaace77]

i type this equation into my calculator and i keep getting .19 not .21. do you have any idea what im doing wrong

[@albertohernandezandrade8919]

How we know that the acceleration is constant?

[@FlippingPhysics]

Newtons' Second Law. The net force is constant, so the acceleration is constant. (The mass is also constant.)

[@rorymoran429]

Outstanding video helped me immensely, thank you very much!

[@FlippingPhysics]

You are very welcome

[@Caitlinoh]

hi, i was wondering why you didn't include kinetic energy in your equation?

[@zaidhussain9123]

because kinetic energy is not needed to find the coefficient of kinetic friction.

[@newtube553]

It was really cool. More uploads please

[@FlippingPhysics]

Always working on videos. They take time though. flippingphysics.com/making-a-video.html

[@josephs.7960]

Wish I had these guys next to me in class

[@harryjamespotter9437]

Thank you sir, Video is so helpful!

[@kennethmcneil9540]

At point 2:16 in the video it is stated that, ma = m(0) =0, how is acceleration 0 when that book is in motion in the beging of the expariment?

[@FlippingPhysics]

The acceleration of the book perpendicular to the incline is zero. The book never moves in a direction perpendicular to the incline.

[@kennethmcneil9540]

​ @Flipping Physics Ah, I know this may be really nerdy but is there a way I can send you a PDF? I just finished my Lab 4 Exercise and I am very proud of it. I have been using all of you'r videos to teach me in the college PHY 201 class. So I kind of am looking at you as my teacher right now vs. the proctor of the class. Haha. I just want to show off how amazingly I imported my equations into my Lab Report.

[@FlippingPhysics]

You can always send me an email [e-mail]

[@ronak859]

Hey I need help with this! Why exactly does the co-efficient of kinetic friction increase with the angle of inclination. I'm using this in my report and I'm getting some pretty confusing answers online. I am on a deadline so it would honestly mean the world if yoou could reply Asap

[@ronak859]

At first I thought that the prosperity of the object would increase increase(steeper = more willing to go down the slope)

[@FlippingPhysics]

The coefficients of friction are independent of incline angle. They only depend on the properties of the two surfaces in contact with one another.

[@FlippingPhysics]

Also be aware that there is a lot of uncertainty in coefficients of friction. www.flippingphysics.com/uncertainty-mu.html

[@ronak859]

@@FlippingPhysics perhaps the uncertainty plays a large role but I conducted an experiment in which I concluded that the angle is indirectly co-related with the co efficient friction and I identified the relationship as being indirectly polynomial.(i have included the uncertainties in my investigation) I'm not exactly sure why but I believe it may be because of the unproportionate decline between the normal force and the force of kinetic friction. I'd be happy to share the paper with you! My argument uses substance from this video too.

[@karenwaggoner4214]

Love this! Super entertaining and educational!

[@FlippingPhysics]

Wonderful!

[@rogerdodger8813]

If down the plane is negative why isn't SumF down the plane negative??? making it -mgsin(thetat)+Fr=-ma. making the final formula have a "-a" not a "+a"???. So final formula would mu=(gsin(theta)-a)/(gcos(theta))???

[@ces9180]

Does anyone know how to find the coefficient if you don't have the acceleration of the object? Is it possible to find the coefficient of the net force with using only the mass of the object and the angle of the inclined plane?

[@ronak859]

I think the correct equation is mgsin(x)- Uk(mgcos(x))= ma As the downward force is greater (mgsin(x)) This results in a final equation of (gsinX - a )/(gcosX ) = Uk Uk- co efficient of friction

[@ronak859]

Wait, nevermind. Why am I wrong though?

[@FlippingPhysics]

You have to be very careful with directions. I made down the incline and to the left negative, therefore the acceleration, which is also down the incline and to the left, has to be negative. Your description seems to assume down the incline and to the left is positive, which is not the approach I would suggest.

[@ronak859]

@@FlippingPhysics Thank for clearing that up!

[@bradley7499]

One thing I don't get... please respond... at 2:45 it says that the net force horizontally would be the kinetic friction minus the parallel component of weight. Shouldn't it be the other way around because it moves down the ramp? So it'd be Weight parallel minus kinetic friction? - Thanks!

[@FlippingPhysics]

The force of gravity parallel is both down and to the left, generally those are considered to be negative directions, which is why the Force of Kinetic Friction is positive (up and to the right) and the Force of Gravity parallel is negative (down and to the left).

[@FlippingPhysics]

@@mariconnell5575 Did you watch the whole video?

[@mariconnell5575]

no lol@@FlippingPhysics

[@FlippingPhysics]

@@mariconnell5575 Well, I hope you have now.

[@Deshbhaktii]

How did bo calculated the acceleration = 0.371208 without a calculator and so quickly. ;)

[@dafootlongsub3003]

Thank you! this video was a lifesaver :D

[@FlippingPhysics]

You're welcome!

[@JulienVIDS]

What would you do if you know the final velocity, but not the time?

[@FlippingPhysics]

It is uniformly accelerated motion. You need to know three of the 5 UAM variables to solve for the other two. www.flippingphysics.com/introduction-to-uniformly-accelerated-motion.html

[@JulienVIDS]

Thank you, it was really helpful.

[@FlippingPhysics]

That's great. So glad to help you learn.

[@Hunty69]

this helped so much on my homework, thanks XD

[@FlippingPhysics]

You are welcome!

[@josephelston4101]

This really helped me out! thanks bro

[@FlippingPhysics]

You are welcome!

[@Jason-ke4jf]

Great video as always. :)

[@FlippingPhysics]

Thanks.

[@yarubik]

So Bo just did all of that in his head. Got em

[@adrianmitrousis8407]

Great video!!!!👍👍

[@johngddr5288]

Thank you so much for these videos :) so much fun

[@FlippingPhysics]

Glad you are enjoying them.

[@Hawkman6788]

Awesome video

[@FlippingPhysics]

Thanks for learning!

[@renubaghel7813]

The teacher is op

[@odee9007]

thank you so much!

[@FlippingPhysics]

You are welcome.

[@yajjhajhria3558]

Great video, don't forget to drink water.

[@crimsonfist1408]

are you wearing different color socks? attention to detail... i like it

[@theeht4272]

I don't fully understand it.......but I'm also not completely lost so...progress

[@meriemdz309]

sir u are amazing ^_^

[@FlippingPhysics]

Thanks!

[@hirokinose3901]

Hello sir, can you explain if the angle was on horizontal plane (180 degree). According to you, μk=gsinθ+a/gcosθ is the equation here, but in horizontal plane since sinθ=0 and cosθ=1, does it mean μk=a/g? I would like to do experiment to find COFk (coefficient of kinetic friction) and I am using spring to move the wood block and planning to measure the acceleration. But I am not sure about formula of μk. Plus, I also watched some video from other youtuber before your video as well such as kzbin.info/www/bejne/bJbCfoBnrs-rpZI This one tell me to use formula a=Fnet (50-Ffr)/mass of wood block(10) instead, but does it work it same way? This guy also say that there is sudden drop from static friction to kinetic friction as the push force exceeded the Maximum static friction, which make it to zero. So does it mean Fsf(max)=μsFn have same force as Fkf(max)=μkFn? Sorry for several questions, I really need response asap. Thank you.

[@FlippingPhysics]

A spring will complicate things because the force caused by a spring changes as a function of position (Fspring = -kx) and therefore the net force will not be constant and therefore the acceleration will not be uniform and you cannot us the Uniformly Accelerated Motion Equations: www.flippingphysics.com/introduction-to-uniformly-accelerated-motion.html With regards to the angle, I have a video dedicated to that: www.flippingphysics.com/incline-components.html Please don't just copy other people's equations from other videos, that leads to a lack of understanding. With regards to static vs. kinetic friction, I have a bunch of videos about that: www.flippingphysics.com/algebra.html#newton Best of luck to you!

[@hirokinose3901]

Thank you for quick response, I realised that it is not uniformly accelerated motion. I found other way which is to differentiate the displacement respect to the time twice to find acceleration. Does this work in this case instead? And I understand the body diagram by incline, but my question is that in horizontal plane the angle would be 0, therefore can μk=gsinθ+a/gcosθ be changed to μk=(g+a)/g substitute the value of acceleration from differentiation.

[@gerryboyp.7668]

WTF!!!

[@kamkam1802]

they lost me at 1:58😐

[@mahirpatel1654]

Same we both dumb

[@Tynur1120]

I love you

[@FlippingPhysics]

+TaiCoh It feels good to be loved. Thanks

[@oongaboonga7013]

see this is the thing with physics. at 2:03, that's when I get confused about finding the net force and finding which components equal which. The fact fg parallel equals mgcos0 does not make sense to me

[@FlippingPhysics]

I have an entire video dedicated to that. www.flippingphysics.com/incline-components.html

[@oongaboonga7013]

@@FlippingPhysics your video helped break it down thank you so much