Why does a spinning object change direction before stopping?

Click For Summary

Discussion Overview

The discussion centers on the behavior of a spinning object, specifically a piece of plastic bent slightly upwards, as it spins on a flat surface. Participants explore the mechanics behind its change in direction before coming to a stop, touching on concepts of asymmetry, forces, and friction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the plastic's asymmetric shape contributes to its spinning behavior, suggesting that the mechanism is complex and direction-dependent.
  • Another participant requests clarification on how asymmetry affects rotational motion and proposes a possible connection to static electricity.
  • A different participant asserts that the effect is unrelated to electricity, explaining that the asymmetry causes the object to lean and jam in its rotation, leading to a reversal in direction.
  • Another contribution challenges the previous explanations, suggesting that a free body diagram and analysis of forces are necessary to understand the motion, emphasizing the role of kinetic and static friction in the process.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms at play, with some emphasizing asymmetry and others focusing on forces and friction. No consensus is reached regarding the primary cause of the observed behavior.

Contextual Notes

The discussion includes assumptions about the shape of the object and the conditions under which it is spun. The complexity of the mechanisms involved is acknowledged, but specific mathematical or physical details remain unresolved.

americanforest
Messages
220
Reaction score
0
Why is it that when you spin a piece of plastic bent slightly upwards on a flat surface, it spins normally for a little while, slows down, and then spins the other way for a bit before stopping? My professor did a demo of this in class and didn't really explain it.
 
Physics news on Phys.org
The plastic has a slightly asymmetric shape. The actual mechanism of the effect is very complicated. It only works if you spin it in one direcction, but not the other. You can observe the asymmetry by looking at the reflection of a light in the curved plastic.
 
Can you explain more thoroughly how asymmetry would affect the rotational motion and cause it to spin in the reverse direction? I was thinking it had something to do with Static Electricity. Is that possible?
 
Nothing to do with electricity. The asymmetry causes it to lean over enough so that it jams in its rotation and rebounds the other way. It only happens when you start spinning it in one direction.
 
omg...this is nth to do with asymmtry...i think u must draw a free body diagram...then list down the forces...assume that the prof gave a force at the top of a cylnder for example...the cynlinder woud start to slide...u know that kinectic friction acts at the bottom of the ball...opposite in direction to the force once applied by the prof...the torque applied by the force of prof would start to reduce while the torque of fric. would increase until one point wen it starts to roll...this is wen STATIC FRICTION comes into the pictor...since the ball is at rest in every point of it's motion since it is rolling...static friction is used...this would go on until once point wen the force exerted by the prof. is zero caused by the friction force...since the cynlider is still moving...the friction torque is still being applied...causing the cynlinder to move in the other direction for some time bfore coming to a stop

phew...hope that explains it...i think i am not very clear with the explanation...but life wut meir achuz...the actual mechanism is a wee bit complicated
 

Similar threads

  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 14 ·
Replies
14
Views
1K
  • · Replies 35 ·
2
Replies
35
Views
5K
  • · Replies 3 ·
Replies
3
Views
8K
  • · Replies 34 ·
2
Replies
34
Views
8K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 20 ·
Replies
20
Views
5K
  • · Replies 131 ·
5
Replies
131
Views
8K