Professor, after watching your content I have become more confident in exploring and decoding the subtleties of physics in everyday life. Regards from India.
thank you for letting me understand physics! it felt nearly impossible until I was directed to watch your videos by my professor at community college amidst covid-19.
I hope your channel can come to more people in my country A lot of students in my country don’t know how to learn physics correctly. Therefore they can not know the beauty of physics. Last 1 year, i hate physics and don’t know how to learn. But now you light up my light, my best teacher. I hope i can continue your job in order to make physics shine again in my country.
I am feeling like taking up a career in research in physics, instead of engineering now....after watching your wonderful lectures. Thank you Professor...
Dear Professor I really would like to thank you so much, your lectures and your way of teaching impressed me from the first time I saw your lectures a few years ago, and each time I see them again, I feel the same excitement as the first time when I saw them. So I hope to be like you someday.
Thank you, how can I ever thank you!! My jee exams are coming, and this topic was ghastly for me, as is for most students I believe. And honestly the first lecture series I watched from you. Thank you. I am crying.
You do! We all do. Right here. What I really like is stoping the video, going back. I just wish RU-vid gave finer controls. I usually spend quite a bit longer on the lectures. My wish is for a USB slot in my skull that I could just insert Angular Momentum. At the moment it's like swallowing an elephant. I've gone back to this lecture to try to sort it out. Maybe starting with the tail wasn't the best way...
I'm currently an 11th grader, I find physics an interesting subject and wish to be a physicist but a majority of people from my area view physics only as a subject where they need good score to either become a doctor or an engineer, before watching this lecture, I was learning about classical mechanics from another teacher from my country, and to my shock all he did was show some mcqs on the screen and tell the answer without even explaining how he got them, all he said was"This is a very important question which will be definitely coming in your exams, learn it by heart, note it down or take a screenshot", like dude, are we only studying for the sake of exams? I got really frustrated and then remembered about Walter Lewin's lectures. I'm so glad to have remembered about it and very grateful for these amazing series of lectures.
How good is this guy!?? His talent, passion and attention to detail is something i will aspire to achieve. Thank you so much for sharing these lectures
"Thank u sir for making the lecture so good" THERE IS SOME SPECIAL FEELIN YOUR LECTURES THAT MAKES PHYSICS LOOK MORE BEAUTIFUL. 😊😇😊 "You made my day, because i was struggling to understand these topics" LOVE FROM INDIA🇮🇳
Hi, I'm in the high school where we don't learn much, so I watch your lectures which they taught me that physics is even more wonderful than I taught. Thanks for sharing them for free! Best regards, not from India, but from Slovenia!
Its really gobsmacking that you are so equivocal about the contents and the way you teach ,that exhilaration in you is just amazing sir.Hats off!!!! Love from India! Will really love to meet you some day
It would be a perfect world if teachers did one solid and always supported the theory they present with actual practical examples, just like professor Lewin. This is how you teach physics, you predict, you show, there you go!
Wow I just found this channel after I search on google best physics professor bcz my favourite subject is physics and it's really best lectures and best teaching way ❤️. Thanks walter lewin for this. Now I'm gonna watch whole videos. So much respect from india🙏.
Watch all my 94 MIT course lectures. Start with 8.01, then 8.02, then 8.03. Do all the homework and take all my exams. *I guarantee you that you will then do very well on the Physics portion of any freshman college or JEE exam*
38:52 that derivation made my day, i am very satisfied i always use to wonder how people simulated motion of 3D objects , but now i know if i can parameterize the surface of 3D object i can simple calculate a higher integral and find the center of mass and translate that origin of the object with respect to only the force at center of mass of the object :)..very interesting.
Dear Walter, Thank you for these video lectures. I don't understand the math ( mostly at all ) but I feel I'm learning. This Is the Power of Walter Lewin... :)
the example of the two cars bound together by a spring is AWESOME, because it shows a system that doesn't behave like a rigid solid, where the cm is not an actual point of the two cars. So let cm be a point that behaves so that M*r_cm=sum(m_i*r_i) where m_i are held together by bond forces, not necessarily rigid ones. Beautiful example!
@@lecturesbywalterlewin.they9259 Human’s life is limited but what they contribute to the world is eternal. Your lectures in Physics will change the world and eternal existence. Thank you so much.!
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 Vibrations and Waves by Anthony French CRC Press ISBN 9780748744473 8.03 Electromagnetic Vibrations, Waves and Radiation by Bekefi and Barrett. The MIT Press ISBN 0-262-52047-8
*8.01x Lecture 15* ---- 0:05 momentum 4:30 conservation of momentum 6:30 example 1 11:00 about kinetic energy before & after (Real big deal in Physics) 20:00 never confuse momentum vs kinetic energy 23:10 hold m1&m2 by a compressed spring 28:00 air track 36:00 centre of mass 41:20 find centre of mass 46:13 motion of centre of mass 50:00 tennis racket trajectory *see more here:* zyzx.haust.edu.cn/moocresource/data/20080421/U/01220/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/detail/Video-Segment-Index-for-L-15.htm ----- *We love the way you make Physics interesting!*
First of all, thank you for the awesome lecture on momentum, Dr. Lewin! I absolutely love your lectures and you really do make physics exciting (especially with your examples of momentum in both particles (tiny) and stars (humungous)) It really helps to know the application of momentum. I have a quick question: in the 1D example with the two objects going in the same direction, why does KE decrease again? It makes sense mathematically, but I don't get why that would be the case conceptually? Thanks again.
Two questions concerning the center of mass of the racquet you threw upwards: 1) Wouldn't we take gravity as an external force on the badminton racquet? 2) The center of mass of the racquet follows a smooth parabola and changes direction over the course of time. How is the velocity of the center of mass constant?
1. yes gravity is action on the racquet 2. The velocity of the center of mass is NOT constant. The component in the x direction is constant but not in the y direction.
So technically Energy is not " destroyed ", but dispersed in a different form. I think the terms are really important in order to not create confusion.
Hey there professor! I really loved your videos. However, can we really say energy is destroyed? I thought energy only can be transformed and transferred.
Life Lyrics you could say that mechanical energy is destroyed (since it’s not conserved), but you’re correct that it’s not really destroyed. Rather, it’s transformed into internal thermal energy and transferred to the surroundings as heat and sound waves.
@@dustinl2375 In the real world, this would be the case. However, here we are doing the calculations based on ideal conditions, and so there should be no energy loss. I can understand when the energies get cancelled out due to opposite direction, but getting cancelled in the same direction confuses me.
I always had something special feeling for physics, and Professor Walter Lewin sir, you have amplified it entirely, now I love physics and wanna persuit a career in it... Sir but I have been confused of its job market, please sir give me some advise❤
@@lecturesbywalterlewin.they9259 please sir I need a Professional like you to give me an honest advise😢 Shall I not go for it even I love it? Btw, thanks for your reply... Love from Bangladesh ❤❤
Sir, if a ball in projectile motion hit the ground and lost half of its kinetic energy . Will the momentum be conserved in x direction ( since there is no external force in x direction)
Humble hello hello hello Sir, horizontal velocity is same in projectile motion , now after collision force acts normal to the ground so total exernal force in x direction is zero so momentum in x direction should be conserved..
The experiment at 46:23 CENTRE OF MASS may seem to defy 'physical law' and the prof. BUT it's the irregular camera panning that gives this impression. The poor camera operator was distracted by the bonkers motion of the two cars. It may have been better to keep the camera still, and not zoom in so much. Physics works and I'm still amazed !
two spheres A and B of masses M1 and M2 respectively collide.A is at any rest initially and B is moving with velocity V along x-axis after collision B has a velocity V/2 in a direction perpendicular to the original direction The Mass A moves after the collision in the direction A) theta = tan-¹ (1/2) to x-axis B) theta = tan-¹ (-1/2) to x-axis
Lectures by Walter Lewin. They will make you ♥ Physics. Sir i broken the momentum into x and y axis and took out the required velocity in x-direction and y separately. Then put tan theta = y/x. So the masses cancelled out. And further my y axis velocity came out negative. Am i wrong?
masses cannot cancel out as M2 is not M1. I solved the problem for you which I rarely ever do. *tan(alpha)=M2/2M1* alpha is the angle with the x-axis. This is my last msg on this topic.
Hello Professor Do the velocities of the cars on the airtrack depend on where along the spring you cut? Supposing you cut the spring at a position closer to one car than the other, what effect does it have on the measurements? I realized you cut the spring at the centre all the time. Any reason?
Well, Sir I am guessing that if there are no external forces then the dp/dt is 0 and the centre of mass will be at rest (if initially at rest, as it follows newton's 1st law) and it will not move irrespective of whatever the particles of the system are doing. Am I right professor?
It is not necessarily "no external forces". Ultimately what matters, in order for us to use conservation of momentum is that there is no net impulse from external forces, or it is negligible. This can be accomplished several ways: 1. There really are no external forces, or they are negligible. 2. External forces add up to zero. Such as normal force and gravity, when we study collisions in the horizontal plane. 3. The interaction happens so quickly that impulses from external forces are insignificant compared to impulses involved in the interaction. Example: the ballistic pendulum. Gravity and tension in the strings do act on the system, and do not add up to zero, but the bullet lodges in to the block a lot quicker than the block can rise along the circular arc.
I have a question for you. This question looks at two things, relativity and the conservation of energy. Suppose there are only two objects in the universe, an asteroid and a rocket. The rocket is sitting ontop of the asteroid and they are both stationary relative to each other. Now imagine the rocket accelerates to 99% the speed of light relative to the asteroid (keeping in mind that would require energy to accelerate it). And now lets imagine the asteroid accelerates to 99% the speed of light also and the two objects are now again stationary relative to each other. My question is, now can the rocket once again accelerate to 99% the speed of light relative to the asteroid and can the two objects now repeat this process? If so, now imagine another inertial frame of reference is made, perhaps a planet in the distance, or a moon or even a speck of dust, how would that object view the velocities of the two objects?
Objects, like many faint galaxies in the Hubble Deep field were at a distance of about 13 billion light years from us when they emitted the light. Even though their speeds away from us were a sizable fraction of the speed of light, the light would still travel to us with the speed of light. Since then they have moved substantially due to the expansion of space. They are now 45 billion lyr away from us and their speed relative to us is much larger than the speed of light. The light from them still travels to us with the speed of light but due to redshift, the wavelength is now infinitely high. Thus we see NOTHING!
+Tushar panda Of course the students are allowed to interrupt my lecture. In fact whenever I make a slip on the black board I WANT them to point it out as slips of the pen are difficult to deal with later (slips of the tongue are easy to correct). Yet, no one interrupted me when I made the mistake. However, when I later watched the video I noticed the mistake and I corrected it with some text.
Hi Professor. First of all thank you so much for allowing us to freely view your lectures, in a way your like the physics teacher I never had. I'm am currently learning about momentum and impulse and have a question that I'm getting conflicted answers to from my textbook, and various sources online. The problem the question stems from is a basic conservation of momentum problem, A gun fires a bullet that has a final velocity of V what is the velocity of the guns recoil is and the kinetic energy of both gun and bullet ( Which end up having different KE) . My book explains this by saying the force the gun exerts on the bullet acts over a shorter distance then the equal and opposite force of the bullet on the gun. But this makes no sense to me for equal and opposite contact forces only exists when two object push or pull on each other so how can this force pair act on the bullet for a different distance then the gun. Google explained it by saying that it was because of the mass difference not the distance. However this would still mean that the work done on each object is equal and opposite which isn't the case in the problem
Hi, professor You said that kinetic energy can be destroyed but momentum can not be, so the destroyed kinetic energy will be converted into the potential energy, am I right? Thank you.
momentum is ONLY conserved if there are NO external forces involved in a collision. KE can be destroyed into HEAT and also in PE depending on the collision. If you shoot a bullet into a wooden block the KE of the bullet will all become HEAT.
Namaste 🙏🙏 🙏 sir Remember in 1st lecture you stated that Scaling factor Using femur example Can you please explain me That how thickness of femur of an animal would increase by 1000 times When length of femur is increased by 10 times Or the size of animal is increased by 10 times
Sir, I had a strong temptation to react on this lecture and so am I doing now - you forgot to mention imho a substantial thing and thus where the kinetic energy after the inelastic collison has gone!!! Of course, it decreases but which form it transforms into as the conversation of the total energy always holds!!!
Dear Sir, If I am sitting idle on my chair my momentum is zero. Now if I move forwards or backwards, I have some momentum. This movement was due to internal energy. How is momentum conserved then in this case?
since in vertical direction there is external force mg on mass m then how conservation of linear momentum is applicable I saw a problem of measuring the speed of bullet by firing in vertically suspended Bob of mass m by a string. then applying conservation of momentum principle give the result. but how since there is external force in vertical direction
The net external force in the vertical direction on each "car" is zero. Gravity downward (mg), force from the track upwards (mg). Thus momentum is conserved in the y direction for each car separately and it is conserved in the x-direction for the 2-car system.
Professor Lewin, your lectures have given me a great insight into physics. At 11:12 you asked a question about kinetic energy of the masses. I had a question regarding the same. In the problem, you conserved the momentum of the system. That means that the net external force on the system is zero so the work done by the net force should also be zero and by work energy theorem, the kinetic energy should remain constant. So why did the kinetic energy decrease? Where did the energy go?
total mechanical energy is conserved. PE (spring) + KE of the 2 masses is conserved. Work Energy Theorem on each mass tells you the change in KE of each mass. Net force on the center of mass is zero all the time. Work energy theorem tells you that KE of center of mass never changed; it remains zero throughout.
What would happen if you could amplify the mass inside of a particle inside of the overall mass that was being exhilarated from outside forces then would it be possible to exaggerated that particle beyond the original mass that it was a part of
Dear sir, A man in a closed boxcar(frictionless wheels) shoots a bullet into a target at the other end.What happens during the three stages of the process: first while the bullet is traveling inside the gunbarrel,then while it is in the air,and finally while it is embedding itself in the target.Could you help me in answering this?.
lecture 14,why bounce ball gives light:When you hold a ball above a surface, the ball has potential energy. Potential energy is the energy of position, and it depends on the mass of the ball and its height above the surface. The formula for gravitational potential energy is PE = mgh where m is the mass of the ball measured in kg, g is the gravitational acceleration constant of 9.8 m/se c2 , and h is the height of the ball in m. As the ball falls through the air, the potential energy changes to kinetic energy. Kinetic energy is energy of motion. The formula for kinetic energy is KE=1/2 mv 2 , where m is the mass in kg and v is the velocity in m/sec 2 . Both potential and kinetic energy have units of Joules (J). As the ball falls through the air, the Law of Conservation of Energy is in effect and states that energy is neither gained nor lost, only transferred from one form to another. The total energy of the system remains the same; the potential energy changes to kinetic energy, but no energy is lost. When the ball collides with the floor, the ball becomes deformed. If the ball is elastic in nature, the ball will quickly return to its original form and spring up from the floor. This is Newton's Third Law of Motion- for every action there is an equal and opposite reaction. The ball pushes on the floor and the floor pushes back on the ball, causing it to rebound. On a molecular level, the rubber is made from long chains of polymers. These polymers are tangled together and stretch upon impact. However, they only stretch for an instant before atomic interaction forces them back into their original, tangled shape and the ball shoots upward. You may be wondering why the ball does not bounce back to its original height. Does this invalidate the Law of Conservation of Energy? Where did that energy go? The energy that is not being used to cause motion is changed to heat energy or sound energy. After playing a game of tennis or racquetball, you will notice that the ball is warmer at the end of the game than at the beginning because some of the motion energy has been changed to heat energy. Because bouncy balls have tightly linked polymers, most of the energy is transferred back to motion so little is lost to heat or sound energy, and the ball bounces well. This is the way the Happy Ball behaves. The Sad Ball has different characteristics. When it is dropped from the same height onto the same surface, it does not bounce even though it has been given the same amount of potential energy as the Happy Ball. It does not bounce because it is made up of a different material. Unlike the Happy Ball which is made of Neoprene, or common rubber, the Sad Ball is made of Norbonene. On a molecular level, Norbonene is different from Neoprene because Norbonene's polymers are more loosely arranged and rub together more when the ball deforms. This additional movement results in motion being converted to heat energy; instead of the ball bouncing, it gets warm. There are several ways to make the Sad Ball happy. One way is to change the temperature of the ball. When the Happy Ball is cooled, its molecules are not as flexible, causing the ball to rebound a smaller distance. When the Sad Ball is cooled, the Norbonene polymer does not deform as much, so less energy is converted to heat energy and the ball bounces. If the Sad Ball is heated, the same process occurs and the ball bounces. Neoprene and Norbonene have many uses besides bouncy balls. Neoprene is commonly used for wire and cable jacketing, automotive gaskets, seals, hoses and tubes, power transmission belts, foamed wet suits, latex gloves and balloons, as waterproof membranes, and for asphalt modification. Neoprene is flexible in its uses because it resists degradation from the sun, ozone, and weather. It performs well when in contact with oil and chemicals and is useful over a wide temperature range. It also resists burning better than exclusive hydrocarbon rubbers and resists damage caused by flexing and twisting. Doping of the Neoprene polymer allows for more versatility and optimal performance. Norbonene rubber has impact absorption uses. It is used as a damping material in shock absorbers and for the protection of conveyor mechanisms. It is used as a padding material in items such as body armor, helmets, sports gloves and mitts, and in the soles of shoes. It is also widely used as an industrial packing material. Stereo speakers make use of Norbonene to minimize resonance and external vibration. Happy and Sad Balls behave differently in a variety of situations. They roll down a ramp at different speeds, they emit sound waves at different decibels, and they bounce different heights on different surfaces. They can be compressed dissimilar amounts when the same force is applied and they are different densities, so they sink in different solutions at variable rates. Allow students to play with the balls for a while and experiment with dropping and rolling the balls to allow them some time to compare and contrast the behavior of the balls and for creative ideas to occur. The time frame for completing the lab is approximately 90 minutes, although this can be modified by reducing the temperatures tested to three instead of five, or splitting the class into 5 groups where each group tests only one temperature and then places their results on a class data table. Achieving exact temperatures is unnecessary; near 00C and near 1000C are easy to get through the use of ice and by boiling water. Room temperature is near 200C.
Hello mr. Lewin Around 10.30, you talk about the decrease of kinetic energy, but where does this energy go? Does it become thermal energy due to the internal force of the collision? Later, you talk about an explosion, which splits a block and increases the kinetic energy, where does it come from?
when KE decreases when negative work is done on an object it can be converted in to PE and/or heat. KE can increase when work is done on an obejct. Work-energy theorem.
