Which attains more height and why?

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Discussion Overview

The discussion revolves around the comparison of two disks, A and B, rolling up inclines with different frictional conditions. Participants explore the implications of friction on the conversion of kinetic energy to potential energy, and how this affects the height attained by each disk. The conversation includes theoretical considerations and practical analogies related to physics concepts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that disk A, which experiences friction, converts both translational and rotational kinetic energy into potential energy, potentially allowing it to attain greater height.
  • Others argue that disk B, which rolls on a frictionless surface, will maintain its speed due to the absence of external forces, leading to a different energy conversion scenario.
  • A participant questions where the rotational kinetic energy of disk B goes, noting that without friction, it does not dissipate but continues to rotate at its initial angular velocity.
  • Some participants assert that under ideal conditions, both disks could theoretically attain the same height, as neither is accelerating due to their rolling motion.
  • There is a discussion about the role of gravity and friction, with some suggesting that friction actually aids in achieving greater height for disk A.
  • Mathematical equations of motion for disk A are presented, emphasizing the need to account for the incline's angle in calculations.

Areas of Agreement / Disagreement

Participants express differing views on the effects of friction and the resulting energy transformations, indicating that multiple competing perspectives remain. There is no consensus on which disk attains more height, as arguments for both sides are presented.

Contextual Notes

Limitations include assumptions about ideal conditions, the specific definitions of rolling without slipping, and the effects of friction on energy conversion that remain unresolved in the discussion.

Shahid0072
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Hi..A disk A and disk b are rolling without slipping with same speed on a horizonal surface..Disc a rolls up an incline and disk b rolls up an incline except that it is fricitionless! Which disk attains more height nw why?
 
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Try relating your Physics homework problems to your real life. Maybe you like to bowl. Imagine a bowling lane with an incline at the end instead of pins. Case A - You bowl your ball on a normal bowling lane at normal strength. Case B - You bowl your ball on asphalt at normal strength.

Once you've pictured a real world situation ask yourself simple questions:

(1) Which lane has more friction, Case A or Case B?
(2) Which ball will make it higher up the incline, Case A or Case B?

Put the two together and WahhhhLA. You understand a little bit of Mr. Newton
 
Cute problem... obviously the "without slipping" part is limited.
 
Thanks for replying guys.Are you saying that in Case of disk A Both translational and rotational kinetic energies will be converted into potential energy..But in case of disk b,only translation kinetic energy will be converted to potential energy as there is no friction to support rotation! But where is that rotational kinetic energy go? Will it be wasted? If yes,how? There is no dissipative force present!
 
Shahid0072 said:
But where is that rotational kinetic energy go? Will it be wasted? If yes,how? There is no dissipative force present!
Without friction, the rotational energy doesn't go anywhere. The disk keeps rotating at whatever angular velocity it had when it entered the frictionless surface.
 
theoretically speaking based from the situation disc B would certainly the one that would gain the greater height because according to Newton's 1st law of motion, "a body that stays at rest remains at rest and if it is moving, it will move at a constant speed." in this case disc B will experience no external forces that may cause it to accelerate nor to deccelerate like frictional force which is present on disc A. thus it will move at a constant speed and it will never stop until reaches the highest point.
 
near said:
theoretically speaking based from the situation disc B would certainly the one that would gain the greater height because according to Newton's 1st law of motion, "a body that stays at rest remains at rest and if it is moving, it will move at a constant speed." in this case disc B will experience no external forces that may cause it to accelerate nor to deccelerate like frictional force which is present on disc A. thus it will move at a constant speed and it will never stop until reaches the highest point.
You forgot about gravity. And don't forget that in some situations--like this one--friction can actually help you go higher.
 
Under ideal situations both will attain the same height considering the fact that the disks are not accelerating/de accelerating by virtue of their rotating motion.

When A goes up that slope, it rolls and so there's no friction stopping it's motion...only gravity is doing that. Same is the case with disk B.
 
  • #10
dE_logics said:
Under ideal situations both will attain the same height considering the fact that the disks are not accelerating/de accelerating by virtue of their rotating motion.

When A goes up that slope, it rolls and so there's no friction stopping it's motion...only gravity is doing that. Same is the case with disk B.
When they hit the slope, A experiences friction but B does not. That makes a difference.
 
  • #11
thanks for replying all...doc is right ...friction helps in disc A in attatining more height as rotational kinetic energy is utilised and in case of disk B only translation kinetic energy is utilised...doc Al ..can u please correct me if i am wrong!
when disk A of mass M goes up an incline,equations of motion are (assuming friction is enough for rolling without slipping)
translation:Mg-friction(f)=ma
rotation:fR=mR^2/2 * a/r
 
  • #12
and friction is acting upwards..
 
  • #13
Shahid0072 said:
thanks for replying all...doc is right ...friction helps in disc A in attatining more height as rotational kinetic energy is utilised and in case of disk B only translation kinetic energy is utilised...doc Al ..can u please correct me if i am wrong!
You are correct.
when disk A of mass M goes up an incline,equations of motion are (assuming friction is enough for rolling without slipping)
translation:Mg-friction(f)=ma
rotation:fR=mR^2/2 * a/r
The only change I'd make would be to account for the angle of the incline: Use mg sinθ, instead of mg.
Shahid0072 said:
and friction is acting upwards..
Absolutely.
 
  • #14
oh yea ..mg sinx ..m silly
 
  • #15
thank you so much...
 
  • #16
doc al..sir just in case you are not super busy...it will be great if you could reply to my angular momentum thread..
 

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