f1_mud - Lecture F1 Mud: Intro Concepts &...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Lecture F1 Mud: Intro Concepts & Definitions (40 respondents) 1. Explain PRS #1 (1 student) For a fluids situation to b e Hydrodynamic or Aerodynamic in nature, the fluid must b e moving relative to an object. In the PRS question, the water does not move past the buoy. So that’s an example of Hydrostatics. 2. Why is p = lim �Fn /�A, and not just F /A ? (1 student) This is just notation convention. The definition is similar to that of a derivative, where �A b ecomes dA in the limit. Later in the course we will write dFn = p dA when integrating all the pressure forces on a wing. 3. If the observer frame changes, wouldn’t p(x, y , z , t) be different functions? (6 students) Very good question. I think I was unclear on what I meant by “same” or “different”, b oth on the PRS question and in the discussion. Yes, the two observers will see different p(t) time traces at each observer’s origin (x, y , z ) = (0, 0, 0), for example. But at the instant when the two origins cooincide (obesrvers are momentarily on top of each other), the two p(t) values will be numerically equal. Likewise for the two �(t) traces. But the V (t) and po (t) traces will not be numerically equal. 4. How can you tell when a scalar field is the same for different observers? (1 student) There’s no guaranteed litmus test. You have to look at the physical situation and decide. This is one job of a physicist. 5. If po is a “pressure quantity”, why does it depend on the observer, unlike p? (1 student) It’s partly b ecause po is a somewhat hypothetical quantity which isn’t directly measur­ able at a p oint, unless you intentionally bring it to rest (drive V � 0). One observer’s definition of “at rest” is different from another’s. We’ll cover this more later. 6. In which frame will po b e most useful? (1 student) Great question! In most cases, po is most useful in that frame in which the flow is steady. It’s useful to an observer moving with the airplane (steady flow). It’s less useful to a stationary observer who sees the plane fly by (unsteady flow). 7. No mud (29 students) ...
View Full Document

This note was uploaded on 01/28/2012 for the course AERO 16.01 taught by Professor Markdrela during the Fall '05 term at MIT.

Ask a homework question - tutors are online