Torque and Center of Mass

A torque causes rotation. Torque = force x lever arm (the distance of the force from the axis of rotation). The example shown in the video demonstrates torque well as it shows the two sides of the ruler have the same lever arm and their torques are equal so the ruler is balanced on his finger. When I say the torques are "equal," I mean that the counter-clockwise torque on the left side of the ruler and the clockwise torque on the right side of the ruler are equal to each other so they balance each other out. This video, although it does not go into detail, also shows the center of mass. The center of mass is the average position of all the mass of an object. When gravity acts on this point, it is the object's center of gravity. The object's center of gravity is right where the man is supporting the ruler with his finger, which is another reason why it is balanced. 
I think this video is a good resource because it explains torque very clearly and in a lot of detail. The end of the video is actually more advanced than the material we covered in class; we did not learn about the equations he uses. But despite this, I think the rest of the video is clear and helpful. The demonstration shows torque really well, as well as center of gravity even though it does not explicitly go into detail about center of gravity.