- #1

vjk2

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Off hand this doesn't make sense. But the math seems to suggest it...

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- Thread starter vjk2
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- #1

vjk2

- 90

- 0

Off hand this doesn't make sense. But the math seems to suggest it...

- #2

Doc Al

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Why do you think this?if I spinned a flat blade (eg: no lift) clockwise it should go up, and counterclockwise it should go down in accord with what I've been taught so far about the cross product as it relates to statics.

- #3

collinsmark

Homework Helper

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Off hand this doesn't make sense. But the math seems to suggest it...

I think you might be referring to the

Angular velocity has a direction which is perpendicular to the instantaneous velocity of any point on the object that is actually spinning. In other words, the angular velocity points along the axis of spin. But there still needs to be some convention about which way, along the axis (up or down), the vector points.

There is a convention called the "right hand rule" that says if you put your fingers along the direction of spinning, such that spinning starts at your hand and works its way out to your fingertips, then your extended thumb points in the direction of the angular velocity vector. But this is just a convention.

Hypothetically, the convention could have just as easily been defined using the "left hand rule" such that the angular velocity's direction is always defined using the left hand. If that rule were made instead, and it was

But to ensure that you get the same intermediate answers that your instructor/text book expects, make sure you use the right hand rule (not the left hand rule). Angular momentum, angular velocity, angular acceleration, and torque are all

(By the way, as you've described it, the right-hand-rule applies to your particular blade analogy, only if you are below the blade, looking up at the whole thing.)

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