Plank Movement in Empty Space: Rotate or Move?

  • Context: Undergrad 
  • Thread starter Thread starter adjacent
  • Start date Start date
  • Tags Tags
    Movement
Click For Summary

Discussion Overview

The discussion revolves around the motion of a plank in empty space when a force is applied to it. Participants explore whether the plank will rotate, translate, or both, and consider the implications of applying forces at different points on the plank. The conversation touches on concepts from Newton's laws of motion, including translation and rotation, as well as the moment of inertia and torque.

Discussion Character

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

Main Points Raised

  • Some participants question whether the plank will rotate or move straight when a force is applied to the side.
  • Newton's second law for translation and rotation is suggested as a framework for analysis.
  • There is confusion about the terms "moment of inertia" and "torque," with some participants seeking clarification.
  • One participant proposes that the motion of the plank will involve both translation of the center of mass and rotation about the center of mass.
  • Another participant inquires about where to apply a force to achieve straight-line motion without rotation, leading to the suggestion that the force should be applied at the center of mass.
  • Concerns are raised about the behavior of the plank after the force is removed, with one participant stating that the center of mass will continue moving in a straight line at constant speed while the plank rotates about its center of mass.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the plank's motion when a force is applied, particularly regarding rotation and translation. While some agree that applying force at the center of mass results in straight-line motion, there is no consensus on the overall behavior of the plank after the force is removed.

Contextual Notes

Participants reference Newton's laws but do not fully resolve the implications of applying forces at different points on the plank. There is also a lack of clarity regarding the definitions and applications of torque and moment of inertia.

adjacent
Gold Member
Messages
1,552
Reaction score
62
Here is a plank in empty space(There are no forces except one) .Someone is pushing it on a side.Will it rotate or Move straight in the direction of the force?
 

Attachments

  • egjlfk.png
    egjlfk.png
    477 bytes · Views: 487
Physics news on Phys.org
adjacent said:
Here is a plank in empty space(There are no forces except one) .Someone is pushing it on a side.Will it rotate or Move straight in the direction of the force?
What do you think? Apply Newton's 2nd law for translation and for rotation.
 
Doc Al said:
What do you think? Apply Newton's 2nd law for translation and for rotation.
I don't quite understand that.:confused:
 
Write down ##F = ma## and ##\tau = I\alpha## for the system you drew.
 
WannabeNewton said:
Write down ##F = ma## and ##\tau = I\alpha## for the system you drew.
OMG!What's ##\tau = I\alpha## ?
 
adjacent said:
OMG!What's ##\tau = I\alpha## ?


Something that doesn't easily hit in google :)
Try googling for "moment of inertia" and "torque"
 
Doc Al said:
See: Newton's 2nd Law: Rotation
I have not heard about anything about the moment of inertia or angular acceleration.Anyways,The plank will rotate,Am I right?
 
adjacent said:
I have not heard about anything about the moment of inertia or angular acceleration.Anyways,The plank will rotate,Am I right?
The motion of the plank will be a combination of the translation of the center of mass plus rotation about the center of mass. It will rotate as well as translate.
 
  • #10
Doc Al said:
The motion of the plank will be a combination of the translation of the center of mass plus rotation about the center of mass. It will rotate as well as translate.
Then where should I apply a force so the plank will only move straight without rotating?On the center of Mass?
 
  • #11
adjacent said:
Then where should I apply a force so the plank will only move straight without rotating?On the center of Mass?
Yes, at the center of mass.
 
  • Like
Likes   Reactions: 1 person
  • #12
When I apply the force on the sides it will rotate and translate,What will happen if I remove the force.Will the plank keep rotating and translating or Move in a constant velocity in a straight line?
 
  • #13
adjacent said:
When I apply the force on the sides it will rotate and translate,What will happen if I remove the force.Will the plank keep rotating and translating or Move in a constant velocity in a straight line?
When you remove the force, the center of mass will continue moving in a straight line at constant speed. And the plank will continue to rotate about its center of mass with a constant angular velocity.
 
  • #14
Thank you So much Doc Al
 

Similar threads

Undergrad How Does Centrifugal Force Affect Objects on a Rotating Disk?
  • · Replies 18 ·
Replies
18
Views
3K
High School Busting the myth about achieving artificial gravity by rotating a body
  • · Replies 38 ·
2
Replies
38
Views
3K
Undergrad How does an object know how far to move when it's moving?
  • · Replies 7 ·
Replies
7
Views
2K
Correct statement about movement of curve ball in a fluid
  • · Replies 9 ·
Replies
9
Views
1K
Undergrad Is it possible to "violate" momentum at the expense of more energy?
  • · Replies 2 ·
Replies
2
Views
1K
High School Newton's Third Law in space
  • · Replies 20 ·
Replies
20
Views
3K
Graduate Rectilinear movement seen from a rotating reference frame
  • · Replies 17 ·
Replies
17
Views
3K
High School Move in Space without mass exchange
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Newton's second law for rotations
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Stuck in understanding Newton's 3 laws
  • · Replies 18 ·
Replies
18
Views
3K