Today in class we covered problem 6/216 on page 72 of the notes. Dr. Krousgrill said in class that the angular acceleration when the rod and disk are at the point shown is zero. I agree with that.
However, he said that this means that angular acceleration was then zero for all time. Was he referring to the angular acceleration of the rod/linkage combination? Or was he talking about the disk rotating on it's pin joint on the linkage?
If angular acceleration was zero for all time, how did the disk/linkage combination start moving and obtain a rotational velocity?
Thanks
Alex Taylor
3 comments:
Alex:
In my notes I have that the angular accelaration is 0 for the disk at all times. I also have that the angular velocity is also zero.
I think the reason the angular acceleration for the disk is zero is because the disk itself is no rotating? I think of it as it is not "rolling" down an incline or something of that sort. Since it is released from rest, the angular velocity of the disk is zero. I hope this answers your question.
Garrett
Garrett is correct. The disk does not rotate as the bar moves. The pin connecting the disk to the bar is not able to transfer any torque between the two. From this, you get the FBD's of the bar and disk that I added to the post (I do not know how to add figures to a comment...). Since there is no moment about A acting on the disk, the angular acceleration of the disk is zero for all tiime. Since it starts with no angular velocity, it remains with no angular velocity.
Good question.
All:
Great, thanks. I understand now.
Alex
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