K.E. and P.E. in a Pendulum and Spring

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    Pendulum Spring
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Discussion Overview

The discussion centers on the conversion of kinetic energy (K.E.) and potential energy (P.E.) during the motion of a pendulum and the compression and expansion of a spring. Participants explore the principles of energy conservation in these systems, focusing on the interconversion of K.E. and P.E. as the pendulum moves and as the spring oscillates.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • One participant requests an explanation of the interconversion of K.E. and P.E. in both the pendulum and spring systems.
  • Another participant asks for clarification on which specific aspects the original poster does not understand regarding K.E. and P.E.
  • A participant emphasizes that at maximum deflection of the pendulum, the bob has maximum potential energy, referred to as PEmax.
  • It is suggested that using basic trigonometry, one can calculate the height of the bob and thus the potential energy at any angle of deflection, denoted as PE(theta).
  • There is a mention of applying conservation of energy, leading to the equation PE(theta) + KE(theta) = PEmax, which can be rearranged to express KE(theta) in terms of PEmax and PE(theta).
  • A later reply acknowledges a previous participant's point, indicating a correction or refinement in the discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the explanation of energy conversion, and there are competing views on the level of detail and effort expected from members in understanding the concepts.

Contextual Notes

Some assumptions about the participants' prior knowledge of energy concepts may be missing, and there is a dependence on definitions of K.E. and P.E. The discussion does not resolve the mathematical steps involved in calculating PE(theta).

Haseeb Ali
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Can anyone explain the conversion of K.E and P.E during compression and expansion of spring and during the motion of pendulum ?
 
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Start with the pendulum. Which bit don't you understand? Do you know what PE and KE are?
 
CWatters said:
Start with the pendulum. Which bit don't you understand? Do you know what PE and KE are?
Yes .. i know that. I just want you to explain the interconversion of K.E and P.E as pendulum moves to and fro ,
 
We're not going to do that. We require our members to put more effort than that into their own learning.
 
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At maximum deflection the bob has maximum Potential Energy. Call that PEmax.

Using Basic trig. you can calculate the bob height and hence the PE at any angle of deflection. Let's call that PE(theta) where theta is the instantaneous angle of deflection.

Then applying conservation of energy...

PE(theta) + KE(theta) = PEmax
or rearrange that to give
KE(theta) = PEmax - PE(theta)

Edit: Sorry russ_watters is right. That's why I haven't calculated PE(theta) for you.
 
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