Rotational Motion: Force on Rod, Translation vs Rotation

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Discussion Overview

The discussion revolves around the effects of force applied to a rod in space, specifically examining the resulting translation and rotation. Participants explore the dynamics of rotational motion, torque, and the relationship between forces and motion in systems like levers and seesaws.

Discussion Character

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

Main Points Raised

  • One participant suggests that applying a force at one end of a rod will cause both rotation about its center of mass and translation of the center of mass.
  • Another participant proposes that the acceleration of rotation and translation can be determined by decomposing the force into components, with one component causing translational acceleration and the other generating torque for rotation.
  • A question is raised regarding whether all the force applied to a lever, such as a seesaw, contributes to rotation.
  • Participants discuss a specific seesaw scenario involving weights and question the force exerted on the fulcrum, considering different weight distributions and net torque conditions.
  • There is a query about the relationship between translation force, net force, and rotational moment, particularly in cases where forces are not balanced.

Areas of Agreement / Disagreement

Participants express differing views on the specifics of how forces translate into motion, particularly regarding the balance of forces and the resulting effects on rotation and translation. The discussion remains unresolved with multiple competing perspectives on the application of forces in rotational systems.

Contextual Notes

Participants' claims depend on various assumptions about the system's configuration, such as the distribution of mass and the point of force application. The discussion includes unresolved mathematical steps related to calculating forces and torques.

Who May Find This Useful

This discussion may be of interest to students and enthusiasts of physics, particularly those exploring concepts of rotational motion, torque, and the dynamics of levers and seesaws.

Moose352
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Imagine a rod in space. If I exert a force at one end, will the rod translate, rotate, or both? How do I determine what it will do?
 
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It will rotate about it's centre of mass, and it's center of mass will move in a translation. Essentially, you are applying a moment and an unbalanced force to the body.
 
But what will be the acceleration of its rotation and translation?
 
Decompose the external force vector into components at the point of application. One componet which passes through the CM of the body the other perpendicular to it. The component through the CM will become a translational acceleration the other component times the distance to the CM will be the torque which cause rotation.
 
So does that imply that when a force is acted upon a lever, like a seesaw, not all of the force acts in the rotation?

Okay, if I had a seesaw of 2 kg, which was 10 meters long, with a child (4kg) at each end, then what would be the force exerted on the fulcrum. Would it not be 2g + 4g + 4g?

What would be the force be if the seesaw became to rotate (that is, the net torque is not 0).
 
Originally posted by Moose352
Okay, if I had a seesaw of 2 kg, which was 10 meters long, with a child (4kg) at each end, then what would be the force exerted on the fulcrum. Would it not be 2g + 4g + 4g?
Yes, it would be.
What would be the force be if the seesaw became to rotate (that is, the net torque is not 0).
Say for example one kid weighs 2kg (small kid). Then the balanced force acting on the fulcrum is 2+2+2 and the rotational force (moment) is 2.
 
So the translation force is equal to: net force - rotational moment = balanced force? In that case, in the earlier experiment, would the translation force be 0 since the force is not balanced?
 

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