Make note that he has taught this lecture numerous times, but every time, for every audience, he delivers energy, excitement, anticipation and joy at the realities of physics. He is one in a billion!
Last comment 6 years ago.... wow. I am a design engineer in the UK, and I just want to say Prof. Lewin, I watch many of your lectures and they have helped me take my understanding, and my career to the next level. I love your lectures. I often fall asleep with one playing in the background. Much love and respect to you always. An inspiration. Thank you so much. Ade
First time(I'm in 11th grade) seeing a physics teacher who is very very clear to his thoughts. The clarity of his thought process and analytical thinking for problem solving has inspired me very much. All my physics teacher mess up every concept they teach, so i dont get a sharp picture of the concept. But watching his videos have made me to love physics. I wanna do research in physics
Sir, I'm an IIT aspirant and always loved physics. just now because of my new physics teacher I felt a little boring while studying physics. but since the time i began watching your lectures, my love for physics has grown to new heights and I'm able to understand the concept to the very core. just want to thank you for what you've done. I'm religiously following your channel these days.
JEE aspirants are blessed and very lucky to have dear professor Walter Liwen helping them with down to earth explanation keeping Philosophy of Nature in the front not mathematics to which many professors succumb to Thank you very much sir and God bless you
Bestest lecture in Physics (of Friction), I have ever seen in my life..!!! Respected Walter Lewin Sir you are Great, simply amazing..!!!💯💯 I am 16 years old JEE Apsirant from India, your lectures give me the realistic feel of Physics, of what is taught in books..!!! Sir please read my comment and if possible please reply, It will make my day..!! 🙏🙏❤❤❤
I sincerely thank you for the explanation on mu, I'm through 3 mechanics classes and 1 physics class, in each one we used mu for loads of different problems but noone explained it to me before what the mu actually is.
I am a 15 years old guy from India.... And we are taught these things for IIT preparation...... In my class... Many students were facing problems.. In this topic and we were crying literally while solving questions of friction combined with pseudo force.... Lift and acceleration..
How lucky are the students of today . They have the internet and have access to great lecturers. During my days as a engineering student in the eighties we had to read all these physics concepts from a book, solve the problems at the end of the chapter to prepare for recitations.
Since the Friction Force = mu * mgcos(alpha) , won't the fictional force also depend on mgcos(theta) = N ? And N also depend on Mass m? I have never found a physics teacher like you , both in knowledge and the ability to explain physics! Truly you are a great teacher !
watch at 5:20 The friction coefficient is independent of mass. That means that if you take 2 objects with very different mass, they will start to slide at the very same angle alpha - *Thus when these 2 objects start to slide you cannot tell what there masses are* Thus the sliding behavor (sliding angle) is NOT a function of mass.
Sir in few lectures, Whenever I watch a new lecture I strongly feel this is your best lecture. But now I realise your every lecture is a best lecture. ❤❤just mind blowing
8.01 Physics Hans C. Ohanian 2nd edition W.W. Norton & Company ISBN 0-393-95748-9 8.02 Physics for Scientists & Engineers by Douglas C. Giancoli. Prentice Hall ISBN 0-13-021517-1 8.03 Electromagnetic Vibrations, Waves and Radiation by Bekefi and Barrett. The MIT Press ISBN 0-262-52047-8
I have the sixth edition and I think it is quite good. One big advantage with the US system using syllabus is that it differs very little between different textbooks. The question and problems from Ohanian is quite easy to find on the internet. The big problem is that you have to study hard between the lessons no matter what textbook you use 😊
I am a 11th class student of PHYSICS WALLAH .And I am revising the lecture. And my teacher Rajwant Sir has made me understand all the concept perfectly that I can understand every words prof. speaks.🙏🙏🙏💓💓
You know I always can't help but watch every lecture of yours that I come across even when they are on a subject that I'm clear with but your demonstration is even more insightful. Thank you so much also for quickly responding to our comments in the comments section. I doubted you'd be able to do that.
I just got into 11th grade and i was feeling down vut after i watched your last lecture in mit i got super motivated ...... thnx for helping sir ..... btw i am from india
I know all the formulas and calculation but don't know how to apply then in real scenario... But when I see your lectures sir this helps me imagining and observing comparing it with real world.🙂😇😇 Genuine Thank You Sir..
It's really nice to see that at the beginning you where apologizing about your voice, but later on you can hear your love for physics as you get more and more enthousiastic about it and you almost don't hear your cold anymore! :D
I just wasted my 2 yrs of jee prep but at last i found sir walter lewin i just got my 90percent syllabus completed through his lectures thanks to a living legend of physics
Thank you so much Sir Walter Lewin. I can't thank you enough, I wasn't able to understand this topic, thanks alot sir I don't have words to explain you're a marvellous teacher. You're literally helping me in my NEET preparation. May God bless you with lots of happiness!
I sell material handling equipment and we sell machinery mover that uses a compressor that blows air underneath and you can push tons around with one hand.I also sell electric forklifts and you lectures on batteries have helped me immensely.Next hydraulics and I will have good working knowledge of those machines far in excess of the manufacturer manual
Wider tires are normally made of a softer compound which has a higher friction but needs to be wider in order for the side wall of the tire to be able to support the weight of the vehicle. So the extra width is necessary because the rubber is softer(so you need more to keep the side wall from buckling)and offers more traction. Also reduces wear because you have a greater contact area. Hope I paraphrased that correctly and clearly.
SIR I AM YOUR BIGGEST FAN FROM INDIA...SIR I ALWAYS WANTED TO LEARN PHYSICS FROM YOU...SIR I AM IN CLASS 11 AND PREPARING FOR IIT JEE...AND I HAD WATCHED ALL YOUR LECTURES FROM THIS CHANNEL...SIR I WISH IN FUTURE I MEET YOU AND HAVE SOME KNOWLEDGE ABOUT THE ULTIMATE LOVING PHYSICS YOU TEACH...REALLY SIR I ASSURE THAT I WILL MEET YOU..AND YOU WILL BE HAPPY TO SEE ME....LOTS OF RESPECT FOR SIR WALTER LEWIN ( THE MAN WHO MADE PHYSICS MUCH EASIER THAN ANYTHING)
I was searching to find a video to help my 2nd year degree s oil m echanics students to understand better the Coloumb's theory (the same French engineer who is also known for the electrical discharge theory) and I've co me across this video. To be very honest, Civil Engineering is nothing but Newtonian Mechanics. We Engineers are applied physicist. Prof ., I really enjoyed your video and will share it with my students if you allow.
hello, i want to ask question, i try to solve assignment (35:00) but i couldn't , because i don't know acceleration and static friction , also WALTER LEWIN shows the formula but i dont understand which one (1) or (2)
I am in 9 grade i started facinating about physic and i am studying from our lecture sometime it is little fast but i slow the video and unterstand the concept here my interestin physic is increasing more and more with the increase in knowlege about physic
According to me race cars have wide tires so that friction applied on tyres is large and avoids slipping(it has a close relationship with velocity) as it allows friction to act in more area as illustrated in your lecture
5:38 Hi sir. I think that it is intuitive that the friction coefficient is independent of the mass of the object. Because if you double the mass, friction will become twice as big, but gravitational force will become twice as big too so the effects cancel out.
first you need to know about traction. traction- traction is force used to generate motion between a body and a tangential surface. So it's like friction between RIGID bodies.(rigid bodies-all points on a perfectly rigid bodies have a relative velocity 0 with each other). Traction can also refer to the maximum tractive force between a body and a surface, as limited by available friction. NOW wider tires have better traction. So there's a misconception that -"wider tires have better traction because of surface area". Soft compound tires are required to be wider in order for the side-wall to support the weight of the car. softer tires have a larger coefficient of friction, therefore better traction. you canjust search it up if you want more details. BUT here a much more complex answer i found on internet when i searched it up - (this copy pasted )- Wide tires were innovated at the request of the legendary Micky Thompson. Thompson had a design for a 1963 Indy Special*, a clever car designed to lower the aerodynamic drag by reducing the frontal area of the car. He made the car as low as possible with the gas tanks on either side between the front and rear wheels and with special ultra low profile tires that barely protruded above the gas tank frontal exposure. The tires were about 50 series at a time when racing tires were all about 80 or 90 series. IIRC, only one manufacturer would build tires like that for him, I think it was US Royal, (UniRoyal), one of the lesser tire companies. The unforeseen benefits of wider tires included a shorter sidewall for less carcass deflection with lower air pressure and a more compliant structure and more rubber surface exposed to the cooling of the road surface and air. Tires like that can run softer compounds without overheating the tread, allowing greater coefficients of friction. The contact patch is relatively shorter and with a more compliant tread, proportionately less contact area is undergoing inferior sliding friction as opposed to superior static friction. LOTS more grip. I don’t believe all these benefits were appreciated with Thompson’s tires, but the manufacturers soon recognized them. By 1965 the wide tire revolution was on! *Indy Special denotes cars built exclusively for the Indy 500 race. They were innovative turbine cars, steam engine cars, tandem wheeled (long before Tyrrell), winged cars (long before Jim Hall) and low-profile tires. Some of them were weird like the Kolbe “Curvebank” car. The early 1960s were the heyday of innovative Specials. NOTE pressure decreases as air molecules in side the wider tire don't collide with as much force as in less wider tire, also the heat from tire expands the tire so wider tires wouldn't burst as easily. ALL THESE WERE FROM DIFFERENT PERSPECTIVES. an engineer's and physicist.
Well friction may be the same but it’s very different when it comes to contact area. Friction generates heat which is produced within the contact area of the tyre, so the larger the tyre, the larger the contact area and thus the heat is generated by a larger surface and will keep the consequent temperature relatively low, so the tyre will not “burn” due to overheating.
i don't know if I'm commenting on the right video but the reason why tires of F1 cars have large surface area is to distribute the weight hence reduce friction, hence fast cars
there was this jee adv question(2010) where they asked to select the graph of force vs friction as one changes force on a block on inclined plane.Thanks to your lecture that i now have the concept to tackle the problem.
It shows that without out resistance , gravity is not pulling stuff directly to the center of the Earth its more resistance that is directing that .And then equal so there must be a cushion of no resistance were it is purely gravity that governs the track of the Moon around the Earth, which they are floating as such
I’m not sure I understand your demonstration of the objects sliding down the incline plane. Clearly, as you show, when the object first moves, mg sin alpha = mu*N = mu*mg*cos alpha. This allows you to compute mu (the coefficient of friction) for a specific object (made of some material) on a specific incline plane (made of some material). Thus, I agree that for a specific object, the surface area of the object that rests on the incline plane does not matter. However, won’t different objects have different coefficients of friction and so the angle at which they start to slide be different? Also, won’t different masses of two objects made of the same material have different coefficients (as mu*N changes) of friction and therefore start to slide at a different angle? In essence, what I am positing is that the experimentally determined coefficient of friction may very well be determined by tangent alpha, but the mu derived only applies to the specifically chosen objects in the experiment. PS. I am one of your biggest fans and you are a stimulant to critical thinking.
Thank you Dr. Lewin. At 5:45 you pointed out that the coefficient of friction is not at all dependent on the mass of the object. I was surprised to notice that your calculation also canceled out g, so that the friction coefficient is also independent of the gravitational acceleration. So I suppose that means that the tires of a truck would have the same grab on a road on the moon, or for that matter on Jupiter, as they would on the earth. Would you agree with that? It seems strange.
+luvinthe jazz The maximum frictional force is proportional to the normal force acting on an object. If you place an object on a table (with friction coeff mu) on Earth the normal force is mg. If you place it on a similar table on the Moon the maximum frictional force is therefore 6 times lower.
+Lectures by Walter Lewin. They will make you ♥ Physics. OK, so the coefficient is the same anywhere, but the different gravitational acceleration will result in a lesser force on the moon, a greater force on Jupiter.
luvinthe jazz these all lectures support that gravity,weight in universe can change but there is one fundamental thing in mechanics that never change and that is mass. It's my point.
@@lecturesbywalterlewin.they9259 Why is there a reforming force? Why do molecules want to regain its position? One more thing, How about a book balanced on a vertical nail?
@@lecturesbywalterlewin.they9259 Still could not understand the physical origin for that restoring force? What if we balance a book on a vertically placed nail? The book will also get deformed.
I am studying Engeneering in Mexico. Now I realize why in the Engineers of the USA are one of the top qualified in the World. And it is because of his teachers.
i would really appreciate if you could answer me this sir Walter lewin; how about the coefficient of static friction for a body moving horizontally and not on an inclined plane
My thoughts nearly exactly Hahaha Nearly ;) Good job And the man's gauntlet on his wrist is true as is necessary for the amount of amazing knowledge he has
I am preparing for IIT JEE but i don't understand physics this leads to getting me down i always be in stress due to this i dont know why i am not able to solve numericals
hello, i want to ask question, i try to solve assignment (35:00) but i couldn't , because i don't know acceleration and static friction , also WALTER LEWIN shows the formula but i dont understand which one (1) or (2)
Sir I am a jee aspirant and I find your lectures really helpful. Can you please tell in which lecture you have covered constrained motion and pseudo force as I have been struggling with that topic. Sir can you also please tell in which lecture you have explained the nature of tension and normal force as despite solving problems and watching lectues on these forces I am not able to understand these forces as clearly as I would like
@Lectures by Walter Lewin, I have watched through the Vedio a lot of times, but I still cannot understand why as the mass increases, the angle it slides down didn't change, because according to the equation: Fmax=muN, as the mass of the object increases, the N must have been also increases, and so mu didn't change, N increases, and so Fmax must increases, this means that it needs more force in order to let in move, as a result the angle should increases in this way of thinking. May you help me to explain the question? Thankyou.
At his previous chapters, he mentioned that x= Vcos(angle) while y=Vsin(angle) due to the triangle shape. For the friction force lecture, at a slanting angle, now the y become =Vcos(angle) while x=Vsin(angle). How? Im confused, pls help anyone?
The trigonometry function that decomposes your vectors is problem-specific, and it depends on how you define your angle and your system of axes. It won't always be cosine for horizontal, and sine for vertical. The simple way to know which trig function to use, is to examine the limits of the angle. Do a thought experiment for the extreme cases, when the angle is 0 degrees and 90 degrees. How does the projection of the vector on the axis in question relate to the angle? We know that sin(0) = 0, and sin(90 deg) = 1, and that the exact opposite is true for cosine. If the vector starts with no projection on your axis in question at an angle of zero, and grows to its full value at an angle of 90 degrees, that would make it sine. If it does the opposite, that would make it cosine. If it starts at zero at an angle of zero, and approaches infinity at 90 degrees, that would make it tangent.
Although I see it in experiments , I don't understand how f_fmax is independent of mass . Because, increase in mass increased the normal force, and thus increases f_fmax. So heavier objects on the same material need more force to overcome friction. But that was not the case we saw in the slope experiments. Where am I going wrong?
Amazing lecture. I have two questions: 1) Ok, I agree that μ = tan θ is independent of the mass. But, maximum static friction force is still Fm = μ x N = tan θ x mg x cos θ = mgxsinθ, which is a function of the mass. So, for m2>m1, we have that the Fm2 > Fm1 and the body 2 would fall latter thatn body 1. 2) I agree that the formula tells nothing about the area. But, what if we have a spherical object and a box with the same material both on the inclined plane. How on earth the spherical one will not fall earlier? thanks.
The angle at which any object with static friction coeff mu starts to slide is independent of the mass. The maximum friction is mu*N which is obviously mass dependent (the larger the mass the larger N). But that is irrelevant. If you have 2 objects one with mass m1 and the other with mass m2 both with the same friction coeff mu then they will start to slide at THE SAME angle theta_slide as tan(theta_slide)=mu. Your conclusion is not correct.
Hello professor Lewin. I have been working hard this autumn with tension and friction. It is very interesting but sometimes very confusing. One of the questions in assignment 3, 3:11, about a woman pushing a wooden box of mass 60 kg on a frictionless ramp did me a little confused. If the ramp was frictionless shouldn’t both the lady and the box sliding down? Else it wasn’t hard to calculate if I supposed she had super shoes.
Thank you for your quick answer. I have only a few questions two answer now and then I will get my reward. That is to look at your 10th lecture about Hooke’s Law and Springs. Thank you so very much for your lectures. I really look forward to see them all.
i have a question. If a circular and rectangular body made of same material is put on a plank. Then the circular body will begin to slide at a very low inclination angle but rectangular body will not do so. NOW the value of static friction is independent of area in contact, then why circular body slides at low angle then that of rectangular body.
If you place a circular disc and a rectangular disc made of the same material (same mu) on a plank they will start to slide at the same angle as tan(theta)=mu. Do not confuse sliding wit rolling. The circular disk should SLIDE. You should therefore place the flat part of the disc on the plank.
Professor, In the video you derive that mu(s) = Tan(alpha), which is in indeed very non-intuitive. This suggests that when alpha becomes zero, Mu(s) becomes zero and the force of static friction is zero. This is not possible right, or am i excluding something in my logic ?
>>>This suggests that when alpha becomes zero, Mu(s) becomes zero>>> If the friction coeff is zero then the object will start to slide at any angle larger than ZERO. THINKKKKKKK
Hello Sir. I have a question. If we imagine there is a perfectly frictionless surface, can a man stand still on it, provided that he doesn't exert any horizontal force? (I think yes)
At min 7:32 you say that a bit of water on the surface of the plank or of the objects that you are sliding will make the friction coefficient larger. However a larger friction coefficient would make the maximum frictional force acting against the object greater and thus increasing the angle at which the object will start to slide; this is a bit counterintuitive as I would say that with water the surface is more slippery and the object will start to slide at a smaller angle. So my question is whether you made a mistake, and if instead water on the surface of the plank would make the friction coefficient smaller??,
my plank is made of wood. It's very smooth uniformly sanded. But the wood is not varnished. If you put a drop of water on it locally the friction coeff will go UP. Do not confuse this with hydro-slipping on the road.
Sir what about rolling friction?? Is it different from the kinetic one.. I came across a inequality which states that mu(s) is greater than mu(k) which is greater than mu(r)..
that's interesting one would think for tires you would multiply by 4 not so.the Friction coefficient for one is the same four 4 if I understood properly thanks that would make a good bet
