What's the "d" in that formula? (work formula)

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  • #4
ZapperZ
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This equation assumes a constant force?
No it doesn't. This is because to find W, you have to integrate F over the appropriate range of dr.

Zz.
 
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  • #5
robphy
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[itex]dW=\vec F \cdot d\vec r [/itex] is an infinitesimal amount work done over the infinitesimal displacement [itex]d\vec r [/itex],
where [itex] \vec F [/itex] is approximately constant during that displacement.

When this is evaluated over a path, then [itex]\vec F[/itex] and [itex]d\vec r [/itex] will vary as you progress along the path.

It's probably not a good idea to think of these [itex]d[/itex]'s as differentials (as in [itex]dW[/itex] is a differential of [itex]W[/itex]
since there is generally no such [itex]W[/itex] because the work done generally depends on the path. In thermodynamics books, this is sometimes written as [itex]đW [/itex].)
 
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