Advance Illustrations – A Bead Sliding on a String | Newton's Laws of Motion #5 for JEE Advanced

Questions asked in JEE Advanced are based on critical thought processes rather than direct application of concepts. For preparation of JEE Advanced, students have to focus on problems based on multi concept applications.

Ashish Arora Sir has taken up a case of A Bead Sliding on a String which is important for select in IIT.

Watch Advanced Illustrations Kinematics videos on various concepts:

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[iliyanparin_iitism]

Simply look it as an action reaction pair, string causes f on bead in upward direction, bead causes f on string downward in the form of tension.

[physicsgalaxyworld]

@shivam, when bead is sliding in downward direction, it experiences friction in upward direction which is generating tension in string so on string this force is in downward direction and on bead friction(or Tension) will act in upward direction...

[SidhRockPhysics]

As the string is not tied with the bead of mass m, so if there were no friction between the string and bead, the tension in the string would be zero and as a result both the bodies will have free fall motion. Obviously, in the given problem, it is the friction force exerted by the bead on the string, which becomes the tension in the string.

[arshitadawra]

Wonderful question and explained beautifully, also the comment section helped me clear all of my small doubts, thankyou for this youtube channel!

[vaibhavsinha]

I am a really big fan of your videos they help me sleep

[OneStopMusic.]

sir why u have equaled tension and friction force and also why you considered tension on bead in downward dirn why not in upward dirn.

[thegamegoing]

sir you could have explained f=t in an easy way
like bead can move through the thread so while moving down thread exerts an upward friction force on bead and same friction force is exerted by bead on the thread in downward direction(as bead wiil see that thread is moving this friction force on string will provide tension to the string.... AM I CORRECT????

[RegisteredLate]

A nice question, tests the fundamentals in that T and f part

[marvel]

I was also having trouble understanding the concept of tension on bead but after reading comments it all got cleared

[pranshumehta]

sir, there is no normal force on bead then why we consider friction force?

[ramanavenkat]

advance illustrations and your 700+ Advance problems book are they same sir please reply sir 🙏🙏

[ishankhandelwal]

sir would you pls elaborate that why tension and friction is equal here ?

[adiosx]

Sir, if friction is equal to tension then, I think bead will move upward . Please clear this doubt sir . Feeling confused.

[gurjeetoberoi]

Sir friction always tends to oppose relative motion so it would act upwards for bead but it would also act downwards for string reaction pair am I right?

[rajeevsharma]

Why we consider relative acceleration here...not just simple acceleration

[ChandaJaiswal-zpok]

Sir please explain the need of using relative motion

[raudreyagupta]

Sir, how do you know for sure that the bead moves downward?
Friction acts because of 2 reasons: 1) mg acts downwards on the bead, and 2) the rod moves down and takes the string along with it. Both these will cause relative motion. So, if friction is greater than mg (which is possible because of reason 2), then won't the beat move up?
Also, I know it doesnt matter for the solution of the problem, but just asking for conceptual understanding..

[chandrasekhar]

My mind has travelled through a wonderful question in this 3 minutes 49 seconds. But I don't know the acceleration of my mind.

[tanmayyadav]

Sir since friction on bead is acting in upward direction.This implies that friction at that point on rope should be downward.But net force on that element is zero which will only be possible when tension acts upward and compensates friction on that element.Where am i going wrong sir??

[closetoheart]

sir we consider pseudo force on rod wrt to moving frame i.e bead