Principle
When a body (such as a sphere or circular cylinder) is spinning in a viscous fluid, it creates a boundary layer around itself, and the boundary layer induces a more widespread circular motion of the fluid. If the body is moving through the fluid with a velocity V, the velocity of the thin layer of fluid close to the body is a little less than V on the forward-moving side and a little greater than V on the backward-moving side. This is because the induced velocity due to the boundary layer surrounding the spinning body is subtracted from V on the forward-moving side, and added to V on the backward-moving side. If the spinning body is regarded as an inefficient air pump, air will build up on the forward-moving side causing higher pressure there than on the opposite side. Another explanation of the Magnus effect is since there is less (forward) acceleration of air on the forward-moving side than the backward-moving side, there is more pressure on the forward-moving side, resulting in a perpendicular component of force from the air towards the backward-moving side. This layer of spinning air, however, is very thin, and it is more likely that most of the Magnus effect is due to the earlier detachment of the air flow on the forward-moving side, which results in a diversion of the flow (acceleration of air) with a perpendicular component towards the forward-moving side, coexisting with an opposing aerodynamic force with a perpendicular component towards the backward-moving side.
Read more about this topic: Magnus Effect
Famous quotes containing the word principle:
“Life is a game in which the rules are constantly changing; nothing spoils a game more than those who take it seriously. Adultery? Phooey! You should never subjugate yourself to another nor seek the subjugation of someone else to yourself. If you follow that Crispian principle you will be able to say “Phooey,” too, instead of reaching for your gun when you fancy yourself betrayed.”
—Quentin Crisp (b. 1908)
“The only principle that does not inhibit progress is: anything goes.”
—Paul Feyerabend (1924–1994)
“If there be one principle more deeply rooted than any other in the mind of every American, it is that we should have nothing to do with conquest.”
—Thomas Jefferson (1743–1826)