The porcupine is very different from other rodents in North America because it is so large, has a big head and, of course, because of its long quills. Porcupines have around 30,000 quills, mostly on their backs and rumps. The longest quills are near the tail and the shortest are on their cheeks.
The divergence of a vector field simply measures how much the flow is expanding at a given point. It does not indicate in which direction the expansion is occuring. Hence (in contrast to the curl of a vector field), the divergence is a scalar.he fact that fluid is flowing out of the sphere is a sign of the positive divergence of the vector field. Rotate with mouse to change perspective. You can move the sphere by dragging it with the mouse.
The divergence of a vector field is the scalar measurement of how much a flow field expands or compresses near a point. The gradient of a scalar function is a vector field. It points in the direction of maximum increase of the function, and the magnitude measures the rate of increase. The curl of a vector field is another vector field quantity. The magnitude measures how much the vector field rotates about each point. The direction is normal to the plane of rotation and is determined by the right hand rule.