Why does a spinning object change direction before stopping?

In summary, the conversation discusses the phenomenon of spinning a slightly asymmetric piece of plastic on a flat surface. It begins by questioning why the plastic spins in one direction, slows down, and then spins in the reverse direction before stopping. The reason for this is due to the asymmetry of the plastic, causing it to lean and rebound in the opposite direction. This is not related to static electricity, as initially thought. The conversation then delves into a more thorough explanation, discussing forces, torque, and the use of static friction to keep the plastic in motion. The actual mechanism is complex, but it ultimately results in the plastic spinning in the reverse direction before coming to a stop.
  • #1
americanforest
223
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.
 
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  • #2
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.
 
  • #3
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?
 
  • #4
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.
 
  • #5
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
 

1. What is rotational motion?

Rotational motion is the movement of an object around an axis or center point. It involves the rotation of an object rather than its linear movement.

2. What is the difference between rotational and translational motion?

The main difference between rotational and translational motion is the type of movement. Rotational motion involves spinning or rotating around an axis, while translational motion involves moving in a straight line without rotation.

3. How is rotational motion measured?

Rotational motion is measured using angular displacement, angular velocity, and angular acceleration. These measurements are typically expressed in radians or degrees per unit time.

4. What are some examples of objects that exhibit rotational motion?

Objects that exhibit rotational motion include spinning tops, wheels, planets rotating around the sun, and the Earth rotating on its axis.

5. How does rotational motion affect the stability of an object?

Rotational motion can affect the stability of an object depending on its center of mass and the distribution of mass around the axis of rotation. Objects with a lower center of mass and a more centralized distribution of mass are typically more stable.

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