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rgirard413

Physics Question(deriving)

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I dont want the answer, just a step in the right direction. I have to derive an equation, but im not really sure i understand what that means. Can anyone help me in the right direction? The equation i have is: static coefficient of friction = tan(theta) again i dont want the answer, just what exactly does it mean that i have to derive this equation? thanks

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Google for "Derivative of tan" or for "Derivatives of Trigonometric Functions"

Edit: Scratch what I said. Despite the vague question, CombatWombat's got his English down better. :D Yeah in that case it would mean "show your deduction process step by step". I still wonder if "derive" can't sometimes mean to take the derivative though, some vague memories from math class keep tugging at me.

[Edited by - lightbringer on November 28, 2005 12:18:57 PM]

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Deriving and a derivative are two different things, I think.

Deriving can mean 'taking a bunch of forumalas and plugging them together to form a new useful formula'. Or by taking some physical meaning and associated formulas and combining them to create an equation which solves for something you want.

If the equation you have there is for friction it is apparently related by the tangent of an angle theta. So you would have to draw the figure and show how you ARRIVE AT u = tan(theta).

If you really need a derivative (the calculus operation) then yes, you will have to look up the derivative of the tan function. You will also need to know what you are taking the derivative in respect to.

I assume you are talking about the first case though.

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that seems like an awful lot of info for just the coefficient of friction.
the coefficient of friction is denoted by a mu symbol in physics (no way to find it on this keyboard, look it up) and is simply the force of "drag" you get on the surface of any object being held down to another object; in our case, earth and gravity are our culprits. it's a really simple number to obtain.
as far as getting it from gathering the derivative of a trigonometric function, that doesn't seem proper, although it may provide a 0.0 - 2.0 result(between air and some adhesive material), which seems likely for a number involving friction.

what are you working on that demands this?

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Guest Anonymous Poster
I think the theta in this formula might refer to the angle an incline must be raised to in order for an object on the inclide to slide off. Deriving it just means showing that this equation is true, using simpler theories that you know are true.

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AP is correct. Draw a diagram of the problem (e.g. a block on an inclined plane that's just steep enough that the block is about to start to slip) - and some lines that have their length proportional to the forces (e.g. friction, gravity, the supporting force normal to the plane etc), and you should be able to derive this relationship based on the physics (in this case, that the limiting friction tangential force is proportional to the normal force).

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