Rigid Bodies Impulse and Momentum Dynamics (Learn to solve any question)

[@guilhermepereira2752]

I don't know if you are going to see this since this video is already more than a year old, however, I'd like to thank you so much for helping me and my housemates get through Applied Mechanics II. I can't express how much you've helped me by simplifing everything, making incredible explanations and pairing them with killer animations, I can't thank you enough really. I wish you the best in life and I want you to know that, eventhough your channel isn't pulling millions of views, by spending your time and effort on KZbin you are helping others and that thousands of people appreciate your honest work. Love from Portugal

[@QuestionSolutions]

I do my best to look through all the comments I get and answer questions, so far so good :) Thank you so much for such taking the time to write such a lovely comment, made me really happy and made my day! Really glad to hear these videos helped you out, and I also wish you the absolute best in your life and all your future endeavors. Keep up the great work!

[@Joedex1625]

hey can you consider providing an equation sheet and then referencing it in your videos? that way I can print it off and study it while i watch and get the concepts better. @@QuestionSolutions

[@QuestionSolutions]

So these videos are just supplementary to your textbooks/course work. They aren't meant as replacements. All the equations used will always be in your textbooks and course materials. The books used are mentioned in the description. @@Joedex1625

[@revaldonkwinika1800]

With this video, you've now covered the entire syllabus of my dynamics course. I should be ready for my exam. Thank you so much

[@QuestionSolutions]

I just need to do one more, the conservation of linear impulse and momentum. Then it'll be the end of main dynamics videos since that should cover everything needed. :)

[@Caleepo]

The 3blue1brown of engineering dynamics/statics

[@QuestionSolutions]

Many thanks!

[@ابراهيمبنعبداللهالسيف]

In this whole semister I have seen your videos multiple of times, very very very well excuted not only the way you simplify things but the visual and these edits are insane and no one can be compared to you, thank you so much

[@QuestionSolutions]

Wow, this was a really nice comment, thank you so very much! I really appreciate it, made my day :) I wish you the absolute best on your studies and future endeavors.

[@Fahimsy3d]

Man honestly thank you so much for creating these videos! Theyre extremely helpful during these uncertain times.

[@QuestionSolutions]

Thank you for taking the time to write a comment like this. I truly appreciate it. You're very welcome and I wish you the best with your studies!

[@Fahimsy3d]

@@QuestionSolutions Not a problem brother. Thank you as well. With exams around the corner, this is beyond helpful. Much love.

[@QuestionSolutions]

@@Fahimsy3d Best of luck with your exams!

[@Fahimsy3d]

@@QuestionSolutions

[@lxnn320]

2 AM right now, studying for a final at 8AM. This channel might single-handedly help me pass. My only grievance is that I didn't find this channel sooner. Thank you so much for the help! :D

[@QuestionSolutions]

You got this! I wish you the best on your final. Do the best you can and I hope all of these videos helped you out. :)

[@lxnn320]

@@QuestionSolutions I got a freaking B in that class and I thought I was gonna fail 😭 All thanks go to You!!!

[@QuestionSolutions]

@@lxnn320 I am super happy to hear that! Well done and keep up the great work :)

[@ginjaturtle]

About to take my dynamics final and this is honestly the best prep I could do, thank you so much!

[@QuestionSolutions]

You're very welcome! I wish you the best on your finals, give it your all 👍

[@ethankinkade4345]

3 years later and this video is helping me pass the class. I have my final exam in 2 weeks that is determining my final grade. This taught me everything we did this whole semeter, and because of this I will pass this damn Dynamics class! Thank you for the time you put into this video, and all your previous ones, subsribed.

[@QuestionSolutions]

Thank you for taking the time to write such a nice comment. I hope you did really well on your exam and I wish you the best in your future endeavors.

[@kinjalchauhan3111]

something i couldnt learn in the entire semester i learnt in 13mins, thank you very much

[@QuestionSolutions]

Glad to hear :) You are very welcome!

[@Lautechh]

usually i never comment, but man, you're the best!

[@QuestionSolutions]

Thank you for the comment! Glad it helped :)

[@menna11954]

at 09:35 why did we add ( mvr) in the angular momentum when we took the mass moment of inertia about point O which is the centre of rotation ? also at 06:30 why didn't we put the final momentum in negative since the gear moves in -ve x-direction?

[@QuestionSolutions]

We need to account for the 40 kg block 👍

[@alishad9777]

Thank you for all these excellent videos! I have a question, if you don't mind. @ 11:14 would it be more precise to show H_o = I_Gw +rmv since the moment of inertia that is used is about the center of gravity of the bars? When I saw I_o I thought you would use 1/3 ml^2 instead of 1/12ml^2.

[@QuestionSolutions]

You are very welcome, and yes, I agree with you, it probably would have been better to use a different notation :)

[@anilerdemulusoy]

I can't put words to explain how much this video helped me. I mean it

[@QuestionSolutions]

Really glad to hear that :)

[@ravirajac]

I really appriciate you efforts and time put into these vidoes. I am gonna go through all the videos on Dynamics for a revision

[@QuestionSolutions]

Glad you like them. I wish you the best with your studies.

[@JulianJArens]

This channel has helped me so much in my education!

[@QuestionSolutions]

I am really happy to hear that. I hope you succeed in all your future endeavors. :)

[@alperenkurt2892]

09:12 , I wish to recommend you to take ccw direction as + for consistency with the lecture books. much more suitable.

[@QuestionSolutions]

Thank you for the recommendation, but years of experience tells me that it's not efficient to do so. You should pick clockwise or counterclockwise based on the equations you need to write. The less you deal with negatives, the faster and easier it is to get to an answer. Pick whichever direction you like, you will get the same answer.

[@alperenkurt2892]

@@QuestionSolutions thank you, all respect to your experince.

[@QuestionSolutions]

@@alperenkurt2892 😅 Best wishes with your studies!

[@oscardegheldere1471]

My man, you are an absolute legend ! Thx so much for the help, your video's are amazing!!

[@QuestionSolutions]

Thank you very much! :)

[@kevinshibu7939]

At (06:48), why did you/ how did you know to use the angular momentum and impulse equation? What was your process of thinking to do this? Why do we not consider the x axis impulse momentum for the wheel, for example?

[@QuestionSolutions]

So there are two ways to know. First, this whole chapter was about momentum and impulse, which makes those equations a given. Second method takes more intuition. When you do a lot of questions, you can, in your mind, come up with a rough idea of how to get the answer you want. Usually, it works out, but if it doesn't, then you try something else. Generally speaking, it's based on a bunch of factors like the givens, what's required, easiest method to get an answer, etc.

[@kevinshibu7939]

@@QuestionSolutions Thank you for the insight, I'm struggling to sometimes comprehend the processes that take place. Hopefully with some more practice questions will make more sense to me. One final question I have is, the 3 equations given at 3:19, are they always applicable regardless of question? Thank you so much for the fast replies!

[@QuestionSolutions]

​@@kevinshibu7939As long as you have the proper givens, yes, they are applicable. It's important to know that most questions can be solved in more than one way. The question is which method will get us the answer the fastest. If speed doesn't matter, use any method you're comfortable with, again, as long as you have enough givens to use that method. And don't worry too much now, the more questions you do, the better you will get at it. You will gain the insight and intuition 👍 Keep up the good work!

[@kevinshibu7939]

@@QuestionSolutions Thank You so much, I really appreciate your dedication and willingness to help.

[@QuestionSolutions]

@@kevinshibu7939 You're very welcome! Let me know if you have any questions.

[@IzzuddinAsj]

thank you so much for this video. honestly the way you explain is so good and easy to understand compare to my lecture class

[@QuestionSolutions]

You're very welcome. Very happy to hear that it was easy to understand :)

[@tylerlim2787]

Good day Sir! Your video is really helpful, it helped me understand the concepts more compared to reading the textbook. I just want to clarify something in Problem No. 1. At (08:09), I noticed that F was equals to 102.04 N. But when I calculated the equation, I ended up with F equals 122.50 N, which I divided it with 200 and got the same time. I hope you can help me out on where I got the equation wrong. Thank you and more power!

[@QuestionSolutions]

I recalculated and I still got the same values shown on the screen. Please see: www.wolframalpha.com/input/?i=%28x%29%28y%29%3D200y-60%2C+0.15%28x%29%28y%29%3D0.46875%2820%29 Could be a numerical error? Not sure 😅

[@tylerlim2787]

@@QuestionSolutions Thanks a lot for the clarification. That was bugging me for a bit, but now it’s all good. Thank you!

[@apexgoblin]

Hello, I'd like to say that your explanations and video-making style is really helpful. It is helping me understand the concepts being taught at school. I wanted to ask is there an online book which you'd suggest for mechanics? A book with derivations to all sorts of topics in classical mechanics with preferrably a mathematical approach. Thank you.

[@QuestionSolutions]

Thank you and I am really happy to hear this style of videos are helpful to you. I am not too sure if there is a single book that covers every derivation of topics on mechanics. The one I like best is Mechanics for engineers by R. C. Hibbeler and K. B. Yap, they have both dynamics and statics as one book, and as 2 separate books. I find their approach to solving problems, their diagrams, and the overall ease of teaching to be the one I list best. In the end, it's hard to say if there is one best book, it depends on how to learn, so my suggestion is to go to your local library and look through the books they have. I find that using multiple books to learn a topic is better than using a singular book, especially with hard concepts because each author takes a different approach.

[@rod8763]

You are a life saver, friend. I don't suppose you plan on doing eccentric impact of rigid bodies, do you?

[@QuestionSolutions]

Thanks! I don't have any plans in the near future to do eccentric impact of rigid bodies. This video does cover impact in some examples: kzbin.info/www/bejne/d5PTipqMhcaYeqs And this video covers the coefficient of restitution. Maybe they will help: kzbin.info/www/bejne/q6vJlpyYaLKefJo Best of luck with your studies!

[@katyar4883]

I'm curious how long it takes to make these videos. Thanks for your effort. My final is in two days and I couldn't have done it without these :)

[@QuestionSolutions]

Quite some time actually :) Glad to hear these helped though, I wish you the best on your finals.

[@ishaanmondal4546]

Lot of thanks buddy your videos save my semester 💕

[@QuestionSolutions]

Glad to hear that! :)

[@jovanmagtoto1682]

thank you sir. Clear and precise. :) I will share it to my classmates

[@QuestionSolutions]

Thank you so much for sharing, really appreciated. :)

[@bell8758]

at 9:30, would that formula on the right side of the equation be the same on the left if it didn't start from rest? H0= Iow +r(mv)?

[@QuestionSolutions]

Yes, but you would need the initial velocities. Everything else would be the same.

[@onatuzkan]

Hello, at the last question why I of rod AB is not considered as fixed axis? I mean rod AB is fixed to point A so instead of 1/12 constant, couldn't we have used 1/3(ml^2) for moment of inertia calculation?

[@QuestionSolutions]

Can you please give me a timestamp so I can take a look and answer your question better? Thanks!

[@onatuzkan]

​@@QuestionSolutionsAt 11:10 when you are calculating moment of inertia;

[@QuestionSolutions]

@@onatuzkan Whether it's fixed or not does not matter here. It's a simple rod, so you can use 1/12mL^2, as long as you find I about the center.

[@s4nti-c-as]

in th gear and rack question what is the intuition behind starting analysis with the rack? is it possible to get the correct answer by analyzing the linear and angular momentum/impulse of the gear?

[@QuestionSolutions]

You can start at any point you like as long as you can keep going. Sometimes, you start somewhere and you get stuck without having enough information, then you need to start somewhere else :)

[@drshspkt2012]

In the energy method where there were two gears we used to equate the change in energy of the system as a whole while in this case we take the change in momentum of two parts individually. Why is that? Is it different when there is a gear and a rack or due to the change in methods?

[@QuestionSolutions]

Please kindly give me timestamps to the places you're referring to.

[@justnapalm392]

Just in time for my Exam!

[@QuestionSolutions]

Best of luck with your exam!

[@mazinalrasbi1356]

at 7:24 why didn't you write the force P=200 and multiply it by the time for the impulse.

[@QuestionSolutions]

Please try it and let me know if you get the same answer. Thanks! :) Keep in mind that we are looking at the gear wheel, not the rack.

[@tarunrajg.mohanraj5885]

thank you! In the last problem, are we assuming the shaft has negligible mass since we don't include its angular momentum?

[@QuestionSolutions]

If the value is not given in the question, it's safe to assume that it's not included/negligible. 👍

[@minmax3160]

I was wondering for angular momentum, when do you use mvr and when do you use Iw, thank you.

[@QuestionSolutions]

Angular momentum will always be with respect to mass moment of inertia multiplied by angular velocity (plus the additional part if its not with respect to the center of mass).

[@dashmoslem]

very informative awesome

[@QuestionSolutions]

Thank you very much!

[@r2k314]

Hello, sir. Is there a way to compute center of mass for the two rods as a single structure and apply the equations. That seems more intuitive. It would be interesting to see if it gives same answer? Thank You.

[@r2k314]

Also, I wholeheartedly agree with last comment by Guilhermeperiera.

[@QuestionSolutions]

Please let me know which question you're referring to. Generally speaking, it's actually easier to find the mass moment of inertia for single objects and add it together than to use it for combined objects, makes it a bit more complicated. Regardless, if you're willing, there is always a way :)

[@r2k314]

@@QuestionSolutions That pretty much answers my question. Thanks.

[@Njabzillah]

In the last question how and why did you assume that the bars are perpendicular?

[@QuestionSolutions]

I actually made a small mistake, there was suppose to be a box symbol at the location where AB and CB meet, indicating it's a right angle. 😅

[@hansvilchez595]

Excellent explanation on the topic. One question: What software do you use for animations?

[@QuestionSolutions]

Thanks! I use after effects for animations.

[@theadel8591]

Why the weight force of the wheel was not included in the free body diagram of the rack ? Why the force P was not included in either free body diagram ?

[@QuestionSolutions]

Force P is shown on the rack FBD (it's the blue force, 200N). The weight of the gearwheel is shown on the gearwheel FBD, but that weight isn't shown on the rack, instead the weight of the rack is shown. We don't add the weight of the wheel onto the rack because the wheel is pinned and only the gears touch, the weight itself isn't added to the rack.

[@xanonymousx6014]

Great job ❤❤❤ I hope if you can do thermodynamics video that will be awesome .

[@QuestionSolutions]

I really want to get to thermodynamics, and a lot of other subjects. I will try to get them as soon as possible. Thank you for your input, I appreciate it.

[@lightningtech8025]

I am struggling to understand where you get the equation for angular momentum about a point outside the rigid body. I don't see it in hibbelers book, after going through about 6 videos I do not see any reference to this equation. Even after going through your video on angular momentum I do not see a reference to it. I also do not see this equation listed in the FE Reference Handbook. I am having trouble deriving this equation and cant find reference to it online, any help is appreciated.

[@QuestionSolutions]

It's under general plane motion, in the chapter that discusses impulse and momentum. See: bit.ly/3Kfep8f

[@Luis-yn8qf]

Wouldn't the moment of inertia of the thin rod connected to the shaft, be (1/3)ML^2 ? I would think this since the rod rotates about its end, not its center of mass

[@QuestionSolutions]

Please provide a timestamp so I know where to look. Thanks!

[@isabelladenooyer9254]

@@QuestionSolutions I had the same question, at 11:30, they can have the same MOI even though their centers of gravity are in different places?

[@franciscoronjansen6563]

good day sir, in the vid 8.05 in wolffrom alpha how did xy=200x-60 become 0=200x-122.5 where did that 122.5 came from?

[@QuestionSolutions]

Sorry, but I don't know where you're referring to. I don't see the -122.5. Where is it?

[@radiatedbug]

Is the mass moment of inertia used for angular momentum always I_G,? (With respect to the center of mass? So no I_o for such problems?

[@QuestionSolutions]

Depends on what the question is asking for. For some problems, it will not be about the center of mass. Especially when it comes to problems with rods, you will find that you might have to calculate it at the edge instead of the center.

[@radiatedbug]

@@QuestionSolutions Makes sense, thank you so muchh!

[@irfnkml..]

hi morning. i want ask you a question. Reaction at pin (Ox and Oy) just only can use at linear impulse ?

[@QuestionSolutions]

Please provide me with a timestamp so I know where you're referring to. Thanks!

[@irfnkml..]

@@QuestionSolutions 4:52

[@QuestionSolutions]

Those reactions exist at all times. The gear wheel will exert a force on the pins. @@irfnkml..

[@Olivia-hu8eg]

do u have a video for eccentric impact???

[@QuestionSolutions]

No, but the coefficient of restitution is pretty much the same when it comes to kinetics. kzbin.info/www/bejne/q6vJlpyYaLKefJo And on this video kzbin.info/www/bejne/d5PTipqMhcaYeqs, we go through impact, just without the coefficient of restitution.

[@jasper4671]

Thanks so much! Tomorrow is my final Dynamics exam 0 --- 0

[@QuestionSolutions]

You're very welcome! Best of luck with your exam.

[@jadkhalil9263]

I'm confused as to why you used rotation about a fixed axis for the second question but not the first, Isn't the first question also rotation about a fixed axis?

[@QuestionSolutions]

We did, I actually mention this at 5:32 saying the gear wheel is a rotation about a fixed axis. Maybe I am not understanding your question, could you clarify what isn't clear? Many thanks!

[@assaidnael8843]

when can we use the formula (Ho)1 = (Ho)2 ?

[@QuestionSolutions]

I am not sure I understand what you mean? It's useful whenever you want to compare momentums.

[@NAYAN-t3e]

Why always angular momentum has been defined about a point instead of an axis but torque is defined about axis ??

[@QuestionSolutions]

You can have angular momentum about an axis too.

[@NAYAN-t3e]

@@QuestionSolutions Then what exactly it means about point ?? Have it some special importance ?

[@QuestionSolutions]

@@NAYAN-t3e A point is exactly what it sounds like, a point. A single small area about which a moment can occur. An axis is basically a "line" in which an object can spin around, or a moment can occur about. This video might offer you some insight: kzbin.info/www/bejne/qJWuYZZvjr-Fj9k Please take a look when you get a chance.

[@wakeawake2950]

First😊😊

[@QuestionSolutions]

Yes! 👍😊

[@jackflash8756]

For the gear and rack example , why isn't F also 200N ? Isn't the rack applying a force on the wheel's teeth of 200N? Also , you made a mistake where the radius of gyration should be 125mm not 0.15m.

[@QuestionSolutions]

No mistake. You are confusing radius to radius of gyration. Radius of gyration was used at 7:13, and radius was used at 5:12. Also, we find the value of F at 8:03, and it's not 200 N.

[@jackflash8756]

This is the definition of radius of gyration: "A radius of gyration in general is the distance from the center of mass of a body at which the whole mass could be concentrated without changing its moment of rotational inertia about an axis through the center of mass." So where did you get the equation I =mk*k ? That seems to be the mass MOI for a hoop , not a solid gear.

[@QuestionSolutions]

You are not using the proper equation when the radius of gyration is given in a question. Go to any website, but for your convenience I got one for you www.pw.live/exams/gate/moment-of-inertia-and-radius-of-gyration/ and scroll to the bottom where it talks about the radius of gyration and how to apply that to find the moment of inertia. This is also in your textbook and I encourage you to review your notes. Always keep in mind, if the radius of gyration is given, the equation to use is I = mk^2. @@jackflash8756

[@jackflash8756]

Many thanks for that link as it makes everything a lot clearer for me.

[@QuestionSolutions]

@@jackflash8756 You're very welcome! Best wishes with your studies.

[@sandovstv6515]

EXAM NA NAMO UGMA SA ENS162 HAHAHAhAHAH THANKS BRO

[@QuestionSolutions]

Good luck on your exam!

[@fra2025]

wow wow!

[@QuestionSolutions]

👍

[@hoanglamvu4885]

i fail Dynamics final exam today

[@QuestionSolutions]

I'm sorry to hear that! Don't be too hard on yourself, if you didn't pass your course, retake it. Utilize office hours with your professor, ask as many questions as you need from your TAs, and do your best.

[@chris_masefield]

shoutout?

[@QuestionSolutions]

👋