Dynamics of rigid bodies physics

Click For Summary
SUMMARY

The discussion centers on the dynamics of a ruler pinned at its center, exploring its behavior when subjected to a downward force. When the ruler is pushed down and released, it will not return to a horizontal position if the center of mass is perfectly aligned with the pivot point. Instead, it will remain in the position where it stops spinning. The equilibrium position is determined by the center of mass relative to the pivot, emphasizing that both horizontal and vertical balance must be considered for stability.

PREREQUISITES
  • Understanding of rigid body dynamics
  • Knowledge of center of mass and equilibrium concepts
  • Familiarity with rotational motion principles
  • Basic physics of forces and torques
NEXT STEPS
  • Study the principles of rotational dynamics in rigid bodies
  • Learn about the effects of torque on equilibrium positions
  • Explore the concept of center of mass in various shapes
  • Investigate real-world applications of rigid body dynamics in engineering
USEFUL FOR

Physics students, educators, and anyone interested in understanding the principles of rigid body dynamics and equilibrium in mechanical systems.

kyin01
Messages
47
Reaction score
0
So the situation is like this a ruler (of uniform mass) is pinned to a nail through its center. The has very little friction so it will spin but come to a stop. Initially it is at rest and is sitting perfectly horizontal (so that means the center of mass is at the center of the ruler).

Now I slightly push down on the right end of the ruler with my hand.

The main question is, after I release my hand ( no more force) will the ruler return to its horizontal resting place it was initially at or will it just remain at the position where ever the spin stops?

This is confusing because when I try this at home with a ruler rotating about my pencil (pencil is through a hole in the middle of my ruler), the ruler always return to some equilibrium position.

However, when I think about it, I don't see any other forces that will make the ruler go back horizontally (due to the center of mass being at the center) after I remove my hand that was pushing down.

So what is going on here? And what's really suppose to happen with the ruler?
 
Physics news on Phys.org
Point is, if the fixed point is not exactly on the center of gravity of the ruler, there will be an equilibrium position when this center of gravity is exactly below the fixed point, due to gravity.
 
vanesch said:
Point is, if the fixed point is not exactly on the center of gravity of the ruler, there will be an equilibrium position when this center of gravity is exactly below the fixed point, due to gravity.

I see what you mean there. So that means given a perfect condition where the center of mass of the ruler is EXACTLY in the center point (point of rotation) so that means left side of ruler = right side of ruler in terms of mass, given those conditions no matter where the ruler stops spinning that's the spot it will remain at rest right? Even if its not horizontal or vertical under those conditions
 
kyin01 said:
I see what you mean there. So that means given a perfect condition where the center of mass of the ruler is EXACTLY in the center point (point of rotation) so that means left side of ruler = right side of ruler in terms of mass, given those conditions no matter where the ruler stops spinning that's the spot it will remain at rest right? Even if its not horizontal or vertical under those conditions

Yes, but the equilibrium has also to be "up/down", not only "left/right".
 
vanesch said:
Yes, but the equilibrium has also to be "up/down", not only "left/right".

Upper part of ruler and bottom part of ruler, ok I'll keep that in mind.

Thanks it really helped!
 

Similar threads

Undergrad Frame Transformation in rigid bodies
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Why does a free rigid body rotate only about its COM when F(ext) is applied?
  • · Replies 7 ·
Replies
7
Views
2K
Graduate Rigid body motion (RBM) transformation
  • · Replies 3 ·
Replies
3
Views
1K
Undergrad The proportion of kinetic energy of a rotating rigid body?
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Manuscript on elementary rigid-body dynamics
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Rigid body mechanics and coordinate frames
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad What Happens When a Rigid Body with a Fixed Point Moves Along a Closed Path?
  • · Replies 8 ·
Replies
8
Views
2K
Graduate Projectile motion of a two-point rigid body
  • · Replies 8 ·
Replies
8
Views
2K
High School Does a body behave as a point mass even at rest?
  • · Replies 38 ·
2
Replies
38
Views
3K
Undergrad Rigid body physics (machine learning environment)
  • · Replies 2 ·
Replies
2
Views
2K