My love for physics has truly been strengthened after watching your videos. You are a gentle and encouraging teacher. I don't feel intimidated or stupid. God bless!
Dan, i'd like to sincerely thank you for taking your time helping us out. Also to congratulate you for your didactic. Keep up the good work friend, greetings from Brazil!
it' is SO easy to realize that I am 65 years old when I am at home on a Saturday Night in January of 2020 and TRULY ENJOYING a Class "A" VIDEO on PHYSICS !!! Thank you Dan !!! Physics RULES...... I enjoy your methods used in your videos. You leave nothing to the Imagination and are so Thorough from beginning to end..... Back in the 1970's, when I studied Physics in college,.. there was NO internet or RUclips... we students either solved these problems or asked for help from the Teacher or T.A.... but Today the Internet is POWERFUL..... do you even remember something called the WORLD BOOK ENCYCLOPEDIA ??? lol.. that was our GO TO reference if we needed to research something... THANKS DAN !!! Keep up the great work and know that your Videos are Truly the best...
Thank you very much Philip... mighty kind of you to say, and just the pick-me-up I needed on a challenging day. So glad you're enjoying physics and that I was able to help in some small way. All the best to you and yours!
Need to say, if i had these materials by the start of my studies i would have struggled much less with the understanding of these basic physical principles. Great work sir, your videos are of utmost quality, you explain the theory and you immediately use it on an example so that it gets fully understood. Keep it flowing! Thank you so much. Greetings from Slovakia
Hi Jocelyn -- great question. If you're referring to the "Energy Conservation Problem 5 minutes into the video, it's just a theoretical construct, not a practical problem. In actuality, you're right, some energy would be lost to friction (internal energy) in a practical application.
My God bro, you're really gonna make my dynamic rotation exam rocks!! It's very useful to those who likes learning with listening poeple explaining . Thanks a lot :D
He meant the moment of force. The Moment of Inertia is the rotational analog of mass, while the moment of force is the rotational analog of force (torque).
Imagine the force the string must be exerting on the pivot... down and to the left, correct? Therefore, the force that the pivot exerts back must be equal in magnitude and opposite in direction, therefore up and to the right! Make it a great day.
They are not. Torque is a force causing a rotation. Moment of inertia describes how hard it is to give an object a rotational acceleration. Similar to, in the translational regime, force and mass.
Wow Dan.... that was a GREAT video.... I had to watch the BOWLING Ball segment Twice to truly Understand it.... lots of Equating going on.... lol ... I'll have to try NOT to think about the ball SLIDING the next time I go BOWLING... otherwise I may bet getting GUTTER Balls... THANKS FOR An Excellent Video!!....
+Philip Y My pleasure. That bowling ball problem is a bit of a bear -- sorry you had to go through it twice, but if it makes you feel better, I think I took about 5-6 takes to get that one down correctly in the video! :-)
I have a question regardings the term. So rolling without slipping is when it basically doesn't skid, and there's rotation + translation? So this would use static friction? and rolling while slipping is just purely translation? and this would use kinetic friction? Also for the rolling while slipping problem, you can use the constant acceleration kinematics because it's being applied constant force by friction?
Hey Dan, For the rolling with slipping problem, the torque created by kinetic friction would have been negative. Why is it that we did not have to account for this when writing out our net torque equation? Thanks in advnace! It was a great video.
what a great video and explanation :) thanks so much you saved my life .. i was struggling for weeks with this subject but you made it so easy to understnad ...keep making videos like this :)
First of all, great video thank you so much! Second, in the last question, why is it that the ball starts rolling when translational velocity equals angular velocity?
+Blaine Brown Hi Blaine. When v=(omega)r, that's the point when the ball rolls on the floor without slipping. The edges of the ball touch the ground at the same rate as the translational velocity. Best way I can think to help is to say try to picture what happens when you throw a bowling ball with spin. For a while the ball spins as it travels over the floor, but it spins faster than its translational velocity (spinning really fast, not really "catching" the floor). The point where it catches the floor is v=(omega)r.
Hey Dan, what if friction did work for the problem where the ball rolls down the incline and you used energy methods to figure out the final velocity? Would we just include the work done by friction on the left side of the energy equation or is it more complicated than that?
Great video, thank you! In the first problem, wouldn't you have to consider the final potential energy as mgR? Because the gravitational potential energy acts on the center of gravity - in this case also is the center of mass - of the disc and it is at height R in the end.
+Caio Vinícius Dallaqua Leal Hi Caio. Great catch. Absolutely, to be perfectly accurate, I should have set the diagram to show H as the height of the ramp, not the height to the center of the disc. Outstanding attention to detail!
I don't understand the difference between your first rolling disc problem and the second rolling disc problem. Is it just that we were not looking for friction that we use the conservation of energy equation? Why are we using FBD and forces in the second?
The first rolling disc "rolling without slipping" turns down the entire ramp -- no slipping or sliding whatsoever. In the following example "rolling with slipping" the ball skids down the alley for a while, then it begins to spin. And I always use free body diagrams and forces to solve these types of problems. All the best! -- Dan
Dan Fullerton You had two rolling without and one rolling with slipping. I understand my issue now, my teacher on Monday says "If you're looking for speed, it's an ENERGY problem. If you're looking for acceleration it's a FORCE problem. If it's a disc then it's a TORQUE problem." (Not that you don't know already, but this helped me a little so maybe it might help someone else who reads this.) Thank you for your videos. So many other videos have a lot of rambling narration and I fall asleep and/or lose attention. I don't even get bored with your videos!
T2R is pulling in the direction we defined as positive, and T1R is pulling in the direction we called negative. Note the beginning of the problem when we picked a direction around the pulley to be called positive. :-)
At minute 25, if you solve for accleration using alpha x R is it two different values. (You get accel=-(mu k)g and accel=5(mu k)g/2R ) These cannot both be true. This makes sense because it is skidding, but then how can you compare rotational velocity to velocity in the same manner.
Hi Chase... in this problem, the first point at which those two quantities are equal is the point at which it is no longer skidding (when v=rw). So if we set those equal to find the time, that time is the exact point at which the ball stops skidding.
@@DanFullerton But then wouldnt the first dirivatives in respect to time have to be equal when you solve for acceleration? Cause you get two different values for acceleration.
@@kaisasong1332 Not all AP physics textbooks cover the same thing, or take 15 chapters to do it. These videos cover a majority of AP Physics C: mechanics. Detailed breakdown here: www.aplusphysics.com/courses/ap-c/videos/APCVidIndex.html (and if you're looking for a guide book, I'd recommend the APlusPhysics books that goes right along with the videos).
Dan Fullerton In the conservation of energy equation we don't take into account work done by friction by subtracting it from the initial gravitational potential energy of the system
No work is done by kinetic friction if the object rolls without slipping, and there's no work done by rolling friction as long as the rolling object and the surface is perfectly rigid.
Dan Fullerton Does this mean that the rotational kinetic energy given by the torque caused by friction multiplied by the distance the disc rolls is already included in the initial gravitational potential energy?
I don't think so... I'm assuming you're talking about 19:28 in the video, when I substitute in for Ma from Newton's 2nd Law... note that little f is the force of friction in this problem, not the net force.
the tensions will provide the torque needed to turn isnt it? since the mass of the pulley acts on the centre of mass of the pulley itself, the torque should be 0. right? im sorry but i am alittle confuse. thanks
Choong Yong Jie The torque due to the weight of the pulley itself is zero, but the torque due to the tension on either side of the rope will not be zero, therefore the pulley will turn. The mass is important. Imagine a 50 gram pulley compared to a 500 kg pulley. The same force exerted on the 50 gram pulley will cause a much larger angular acceleration than that force on the 500kg pulley.
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Wow THANKS SO MUCH for the lesson, much clearer than my teacher! This really helped!
Glad you liked it!
My love for physics has truly been strengthened after watching your videos. You are a gentle and encouraging teacher. I don't feel intimidated or stupid. God bless!
Wow, thanks so much Andrew!
Dan, i'd like to sincerely thank you for taking your time helping us out.
Also to congratulate you for your didactic.
Keep up the good work friend, greetings from Brazil!
it' is SO easy to realize that I am 65 years old when I am at home on a Saturday Night in January of 2020 and TRULY ENJOYING a Class "A" VIDEO on PHYSICS !!! Thank you Dan !!! Physics RULES...... I enjoy your methods used in your videos. You leave nothing to the Imagination and are so Thorough from beginning to end..... Back in the 1970's, when I studied Physics in college,.. there was NO internet or RUclips... we students either solved these problems or asked for help from the Teacher or T.A.... but Today the Internet is POWERFUL..... do you even remember something called the WORLD BOOK ENCYCLOPEDIA ??? lol.. that was our GO TO reference if we needed to research something... THANKS DAN !!! Keep up the great work and know that your Videos are Truly the best...
Thank you very much Philip... mighty kind of you to say, and just the pick-me-up I needed on a challenging day. So glad you're enjoying physics and that I was able to help in some small way. All the best to you and yours!
From Lebanon (M.E) to America ... I salute you Mr. Dan , you're the best and i really was helped by your videos ... Thank you very much :)
You're welcome, and I'm thrilled you're finding these videos helpful!
Need to say, if i had these materials by the start of my studies i would have struggled much less with the understanding of these basic physical principles. Great work sir, your videos are of utmost quality, you explain the theory and you immediately use it on an example so that it gets fully understood. Keep it flowing! Thank you so much. Greetings from Slovakia
+BLefo You're very welcome. Greetings from the USA!
+Dan Fullerton (APlusPhysics) I think you mean 'Murica
Thanks so much -- I really appreciate the positive feedback... it keeps me making new videos!
Great review before the AP Physics C - Mechanics exam!
Hi Khoi -- yes, though often times you'll even find a different coefficient for "rolling" friction.
Hi Jocelyn -- great question. If you're referring to the "Energy Conservation Problem 5 minutes into the video, it's just a theoretical construct, not a practical problem. In actuality, you're right, some energy would be lost to friction (internal energy) in a practical application.
Thank you Dan. I really appreciate you taking the time to make a video to help people like me out.
You just taught me 4 weeks of college physics i was struggling through. You are the best!
Thrilled to hear the videos helped you out!
My God bro, you're really gonna make my dynamic rotation exam rocks!!
It's very useful to those who likes learning with listening poeple explaining .
Thanks a lot :D
Good luck on the exam, and you're welcome!
I skipped my junior year physics. your videos were enough
Thank u
You, sir, have helped me far more than my own professor.
Thrilled to hear you're finding a way to be successful!
Our school doesn't teach Physics C, only B. Thank you so much for these videos to help me learn for the C exam.
WOAH! Wicked Video! I love how clean and organized your work is!
Thrilled you got something positive out of it. Make it a great day!
Thank you so much! My final is in three days and I was still struggling with this topic. You cleared my doubts
Gravity isn't causing a torque because it is acting at the center of mass. Remember, torque=Fr*sin(theta). If r=0, there's no torque (just a force).
You sir, deserve an award. You are a fantastic teacher!
Thanks Alex, mighty kind of you to say!
He meant the moment of force. The Moment of Inertia is the rotational analog of mass, while the moment of force is the rotational analog of force (torque).
Imagine the force the string must be exerting on the pivot... down and to the left, correct? Therefore, the force that the pivot exerts back must be equal in magnitude and opposite in direction, therefore up and to the right! Make it a great day.
They are not. Torque is a force causing a rotation. Moment of inertia describes how hard it is to give an object a rotational acceleration. Similar to, in the translational regime, force and mass.
Glad to hear it, and you're welcome!
Thanks this is really helpful for ap physics 1 . We had to learn rotation practically on our own
Thanks, and good luck on your exam on Monday!
You can have gravity cause torque if you change the pivot of the object from the center of the object.
Tks from India u r the best teacher I found on RUclips.subscribed :)
Glad you're finding these helpful!
Thanks Neil (trust me, it wasn't that clean on the first attempt! :-) Make it a great day!
You're welcome!
Wow Dan.... that was a GREAT video.... I had to watch the BOWLING Ball segment Twice to truly Understand it.... lots of Equating going on.... lol ... I'll have to try NOT to think about the ball SLIDING the next time I go BOWLING... otherwise I may bet getting GUTTER Balls... THANKS FOR An Excellent Video!!....
+Philip Y My pleasure. That bowling ball problem is a bit of a bear -- sorry you had to go through it twice, but if it makes you feel better, I think I took about 5-6 takes to get that one down correctly in the video! :-)
That would seem like a reasonable path to take to me!
I have a question regardings the term. So rolling without slipping is when it basically doesn't skid, and there's rotation + translation? So this would use static friction? and rolling while slipping is just purely translation? and this would use kinetic friction? Also for the rolling while slipping problem, you can use the constant acceleration kinematics because it's being applied constant force by friction?
Hi Dan i just wanted to say that you've got students in Turkey too
Thanks for these great lectures :)
That's awesome, thanks so much for taking a moment to say thank you! Best wishes, good luck, and keep in touch!
You might find the video on "Free Body DIagrams" helpful for answering this question. :-)
great video, do you have any that talk more in detail about the pivot force?
Hey Dan,
For the rolling with slipping problem, the torque created by kinetic friction would have been negative. Why is it that we did not have to account for this when writing out our net torque equation? Thanks in advnace! It was a great video.
Awesome explanation and solving
Glad it's helping! Good luck...
Thank you sir. Excellent video!
what a great video and explanation :) thanks so much you saved my life .. i was struggling for weeks with this subject but you made it so easy to understnad ...keep making videos like this :)
Glad you enjoyed it, and you'll find tons of these videos here and on the APlusPhysics site!
First of all, great video thank you so much! Second, in the last question, why is it that the ball starts rolling when translational velocity equals angular velocity?
+Blaine Brown Hi Blaine. When v=(omega)r, that's the point when the ball rolls on the floor without slipping. The edges of the ball touch the ground at the same rate as the translational velocity. Best way I can think to help is to say try to picture what happens when you throw a bowling ball with spin. For a while the ball spins as it travels over the floor, but it spins faster than its translational velocity (spinning really fast, not really "catching" the floor). The point where it catches the floor is v=(omega)r.
Hey Dan, what if friction did work for the problem where the ball rolls down the incline and you used energy methods to figure out the final velocity? Would we just include the work done by friction on the left side of the energy equation or is it more complicated than that?
Thanks for the video, very helpful!
Glad this has been of help. You might also like the materials under Courses -- AP-C on the APlusPhysics (dot) com site!
You're the man! Thanks
For 9:18 , does anyone know why the force of the pivot is in that direction?
simply fabulous !!
So glad you like it!
Please keep making videos!
Got a couple more in the works!
Great video, thank you!
In the first problem, wouldn't you have to consider the final potential energy as mgR? Because the gravitational potential energy acts on the center of gravity - in this case also is the center of mass - of the disc and it is at height R in the end.
+Caio Vinícius Dallaqua Leal Hi Caio. Great catch. Absolutely, to be perfectly accurate, I should have set the diagram to show H as the height of the ramp, not the height to the center of the disc. Outstanding attention to detail!
great job ,thanks...
How do you know at 15:55 that the bottom is mgcos and the x compenent is mgsin? Sorry my trig is rusty
No problem!
Hello,Shouldn't the torque created from the force of friction be negative due to the right-hand rule?
Sir i shall be obliged if you clarify me the difference between torque & moment of force??
Are these two same thing?
thank you so much for posting this
For rolling without slipping problem shouldn't the Inertia be 1/2mr^2 + mr^2 because friction force and its center of mass is r apart?
Okay, thanks for the help!
At 23:18 why is the net torque not - Fk R?
Hey! I think, For Rolling With Slipping You Cannot Use V=RW , Because for Rolling With Slipping V is not Equal to RW .. Can you please double Check ..
Thank you soo much for posting this!!
You're very welcome!
thank you this is so good
My pleasure!
thank you so much for this video!!
You might find the torque video helpful...
I don't understand the difference between your first rolling disc problem and the second rolling disc problem. Is it just that we were not looking for friction that we use the conservation of energy equation? Why are we using FBD and forces in the second?
The first rolling disc "rolling without slipping" turns down the entire ramp -- no slipping or sliding whatsoever. In the following example "rolling with slipping" the ball skids down the alley for a while, then it begins to spin. And I always use free body diagrams and forces to solve these types of problems. All the best! -- Dan
Dan Fullerton You had two rolling without and one rolling with slipping. I understand my issue now, my teacher on Monday says "If you're looking for speed, it's an ENERGY problem. If you're looking for acceleration it's a FORCE problem. If it's a disc then it's a TORQUE problem." (Not that you don't know already, but this helped me a little so maybe it might help someone else who reads this.) Thank you for your videos. So many other videos have a lot of rambling narration and I fall asleep and/or lose attention. I don't even get bored with your videos!
Thank you very much....
Thank You
Why is T2R positive and T1R negative in the net torque equation for the massive pulley problem?
T2R is pulling in the direction we defined as positive, and T1R is pulling in the direction we called negative. Note the beginning of the problem when we picked a direction around the pulley to be called positive. :-)
Dan Fullerton haha thank you
At minute 25, if you solve for accleration using alpha x R is it two different values. (You get
accel=-(mu k)g and accel=5(mu k)g/2R ) These cannot both be true. This makes sense because it is skidding, but then how can you compare rotational velocity to velocity in the same manner.
Hi Chase... in this problem, the first point at which those two quantities are equal is the point at which it is no longer skidding (when v=rw). So if we set those equal to find the time, that time is the exact point at which the ball stops skidding.
@@DanFullerton But then wouldnt the first dirivatives in respect to time have to be equal when you solve for acceleration? Cause you get two different values for acceleration.
Keep in mind the accelerations are in different directions... @@chasefitch2245
Beautiful
its been 10 years dang
do you cover everything ? from chapter 1 to chapter 15?
Probably depends upon what book you're referring to
Dan Fullerton uh any AP physics textbook
@@kaisasong1332 Not all AP physics textbooks cover the same thing, or take 15 chapters to do it. These videos cover a majority of AP Physics C: mechanics. Detailed breakdown here: www.aplusphysics.com/courses/ap-c/videos/APCVidIndex.html (and if you're looking for a guide book, I'd recommend the APlusPhysics books that goes right along with the videos).
At 5:57 how can the disc roll down the incline with no friction causing a torque?
What makes you say there isn't friction?
Dan Fullerton In the conservation of energy equation we don't take into account work done by friction by subtracting it from the initial gravitational potential energy of the system
Is any work done by friction in this problem?
No work is done by kinetic friction if the object rolls without slipping, and there's no work done by rolling friction as long as the rolling object and the surface is perfectly rigid.
Dan Fullerton Does this mean that the rotational kinetic energy given by the torque caused by friction multiplied by the distance the disc rolls is already included in the initial gravitational potential energy?
you made a mistake when you set f=ma instade of f=1/2na in the equation of the disc roll down the incline
I don't think so... I'm assuming you're talking about 19:28 in the video, when I substitute in for Ma from Newton's 2nd Law... note that little f is the force of friction in this problem, not the net force.
sorry but why is the mass of the pulley taken into consideration when it passed through the point of rotation. it should not cause any torque right?
But the pulley must turn in order for the system to turn. As the pulley now has some mass, we must take into account its rotational inertia.
the tensions will provide the torque needed to turn isnt it? since the mass of the pulley acts on the centre of mass of the pulley itself, the torque should be 0. right? im sorry but i am alittle confuse. thanks
Choong Yong Jie The torque due to the weight of the pulley itself is zero, but the torque due to the tension on either side of the rope will not be zero, therefore the pulley will turn. The mass is important. Imagine a 50 gram pulley compared to a 500 kg pulley. The same force exerted on the 50 gram pulley will cause a much larger angular acceleration than that force on the 500kg pulley.
Dan Fullerton I can fully understand you now. Thanks a lot. You really cleared all my doubts
isn't it =Mp/2*R*a on the right side in 12:55?
It would be, other than I've divided out the R from both sides in simplifying the equation. Make it a great day!
Omg that's tricky
Ha I'm in 10th grade and I semi get this I'm not even in calculus !
Glad you're enjoying the videos!
I'm surviving!!!!
That's an excellent start!
Thank you very much.