"Music is a hidden practice of the soul, which does not know that it is doing mathematics."
-- Leibniz
The class on Monday, October 31, will be a review for the test. It will be all PowerPoint based. You may access a pdf of the PowerPoint with the button to the right. |
We discussed forces on the hip. Supplementary Notes in pdf format are available on this topic. |
We asked only one "clicker" question today. |
The distribution of your answers is shown to the right. Only about one-quarter of you got this correct: C. The mass of the meter stick is one kg. As usual, it is better we found out about this mis-understanding now instead of on the test. In class I discussed two ways of arriving at the correct answer. |
You may wish to check your understanding with the following.
In class we discussed the answer by talking about the torques acting about the actual pivot point. However, since the meter stick and rock are in equilibrium the torques can be evaluated about any point. To analyse about any other point you will need to think about the force exerted on the meter stick by the pivot. The total vertical force acting on the meter stick plus rock is equal to zero.
We used two Flash animations today.
It is perhaps worth emphasising something I tried to stress in class today. Symmetry considerations lead us to assign the direction of the angular velocity vector to lie along the axis of rotation. Then which of the two possible directions it can point is just a convention.
Pdf version of the PowerPoint on the side screens. | |
Today's Journal. |
The arrows let you jump to the previous/next class summaries. |