Why does a spinning object change direction before stopping?

AI Thread Summary
A spinning object with an asymmetric shape can change direction before stopping due to the interplay of forces acting on it. When spun in one direction, the asymmetry causes it to lean, leading to a jamming effect that results in a temporary reversal of motion. The discussion clarifies that static electricity is not involved; instead, the dynamics of friction and torque play crucial roles. As the applied force decreases, frictional torque continues to act, causing the object to spin in the opposite direction briefly. Understanding these forces through a free body diagram can help clarify the complex mechanism behind this phenomenon.
americanforest
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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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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
 

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