Forces Producing Rotational & Translatory Motion: Exploring Mechanics

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Discussion Overview

The discussion revolves around the mechanics of forces producing both translatory and rotational motion in a rigid rod when a force is applied perpendicularly. Participants explore the implications of this scenario through a thought experiment involving spherical bobs and an elastic string.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why a perpendicular force on a rigid rod leads to both translatory and rotational motion, seeking a mechanical explanation rather than a mathematical one.
  • Another participant argues that applying a force to one end of the rod will cause the center of mass to move, implying that translatory motion is inevitable.
  • A different participant expresses confusion about why rotation occurs specifically about the center of mass, suggesting that centripetal forces must balance at this point for circular motion.
  • One participant requests further analysis of the proposed thought experiment involving two bobs and an elastic string to understand the mechanics better.
  • Another participant challenges the relevance of the thought experiment, suggesting that it would lead to simultaneous translation, rotation, and oscillation, depending on the string's properties.

Areas of Agreement / Disagreement

There is no consensus on the mechanics of the situation, with participants presenting differing views on the nature of motion and the relevance of the thought experiment. The discussion remains unresolved.

Contextual Notes

Participants express uncertainty regarding the mechanics involved, particularly about the role of centripetal forces and the implications of the elastic string in the thought experiment. There are also assumptions about the behavior of the system that are not fully explored.

NANDHU001
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Why does a force applied exactly perpendicular to one end of a rigid rod produce translatory motion along with rotational motion about center of mass?
I know the mathematics F=m(center of mass)*a but I want a mechanical answer.
Please help me analyze the mechanics of it.
I think analyzing the following thought experiment will be of some help though i don't
know how to proceed with it.
Consider two spherical bobs attached to two ends of an elastic string.(rigid rod as a limiting case of elasticity)
When an exact perpendicular force is applied at one bob the bob will accelerate and move along a straight line while the other bob remains at rest. Now due to an increase in length
of the string a tension will be developed and will pull both the bobs toward its center of mass.
I don't know how to proceed with it and can't see why the rotation is about center of mass.
 
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Why do you think it should not produce translatory motion? You push the rod in one direction. After your push, one end moves, the other does not, so the center of mass moves, too.
 


NANDHU001 said:
can't see why the rotation is about center of mass
Because you need a centripetal force for circular motion. At the center of mass the centripetal radial forces of both sides balance.
 


Thanks but please consider analyzing the thought experiment I have mentioned.
 


What is so special about that experiment? You will get translation, rotation and oscillation of the string length at the same time (assuming it has compression forces as well).

If the string does not give any force below a certain length, your objects will come closer, but miss each other until they extend the string again, and the whole thing repeats.
 

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