Hello World I can't introduce the concepts of hydrodynamics into my mind,such as the streamline. I can't imagine what is a streamline? What makes us say that the flow is turblant or the flow is steady? --------- "the direction of the tangent drawn at any point on the streamline represents the direction of tangential velocity" so what is tangential velocity? [PLAIN]http://img265.imageshack.us/img265/9021/unled11e.jpg [Broken] I imagine that,this means ,if the fluid particle was to leave the streamline,it will move in the direction and with this tangential velocity.Is that true? --------- "the rate of flow is constant along the path of the flow,since fluids are incompressible" I don't understand.What is the rate of flow? --------- why is the blood flow in aorta faster than the other arteries? I know how to explain this biologically,it is because aorta is the nearest to the heart but if we look at this in a physical point of view,We will find that the cross sectional area of aorta is bigger,so the speed of blood flow in the aorta should be smaller.then how could we explain this physically?may be because the speed of blood flow in Aorta is distributed among those arteries so the speed becomes less in smaller arteries. ----------- I can't imagine at all,what is viscosity? [PLAIN]http://img36.imageshack.us/img36/4862/unled123j.png [Broken] If we imagine a liquid between two plates ,plate A is moving while plate B is not moving Why does the speed of the fluid decreases as we go down from A to B? what is the force of viscosity?and why is this force inversely proportional to the vertical distance between the the moving layer and the layer that is not moving? After answering my questions,could you recommend some good websites about fluids? my favourite website "the physicsclassrooms" usually uses a very simple language I used this website to understand many concepts about waves but misfortunately,there's no tutorials about fluids in this website. P.S I'm really serious in learning and understanding new ideas in the correct way,so please don't let me down.. another P.S my physical knowledge is very basic Thanks in advance..