Understanding about differentials?

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SUMMARY

The discussion focuses on the relationship between arc length and angular displacement in the context of differential calculus. The key formula presented is dl = r dθ, which defines the differential arc length (dl) in terms of the radius (r) and the differential angle (dθ). This relationship is crucial for understanding how small changes in angle correspond to changes in arc length, particularly in physics problems involving circular motion.

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  • Study the derivation of the arc length formula l = rθ
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Homework Statement



Problem 7.29:

http://cas.umkc.edu/physics/wrobel/phy240/Homework 5.pdf

Homework Equations



dr= R d(theta)

The Attempt at a Solution



I don't understand how to get R d(theta) = dr from the last part of the question, any explanation about how it works is appreciated.
 
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It's a formula from radian measure. Basically if you have the angle [tex]\theta[/tex] in radians, you can find the arc length by the formula:
[tex]l=r\theta[/tex]
So if you have a differential amount of [tex]\theta[/tex], you can find a differential amount of arc length which is just [tex]dl=rd\theta[/tex]
 

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