When fluid flows over a plate why can't we use the Fourier's Law of conduction ?
Its true that the layer which is just in contact with the plate surface is not moving along with the flow because of the no slip condition. So heat transfer with in that thin layer is actually conduction. But the temperature gradient at the surface changes for different velocity of the fluid, because of which we can not use the Fourier's Law of conduction and have to use different ways to get the Heat Transfer Coefficients.
What is the difference between stream line and streak line ?
In fluid mechanics when fluid flows, their are many ways to visualize the motion of fluid particles. These two terms help in that. Stream line is basically the line on which if we draw a tangent at any point will give the direction of the velocity of the particle at that point or we can say the motion of the particle at the point. Streak lines are the path followed by the particle during flow. In steady flow streamlines and streak lines are same. You tie a paper ball at some place in a river the direction in which it flows will tell you the direction of the particle at the point. Tying many balls at different place and connecting them gives the streamline. If we cut the thread, the path that the ball follows is the streamline.
What is the difference between mass and moment of inertia ?
Mass is basically the property of a matter why tries to resist the acceleration or the change in its state of motion. Moment of inertia is a quantity(not a property) of a body which tries to resist the angular motion of the body. The difference between them is that mass can not be changed(in Newtonian mechanics) where as the moment of inertia can change depending on the distribution of the mass about the axis of rotation. The more is the mass farther away the axis the more is its moment of inertia.