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## Main Question or Discussion Point

**Confusion over derivation of angular momentum equation**

Hello, I'm a little confused over the relation between torque and angular momentum.

When [tex]L=r×mv[/tex]

[tex]\frac{dL}{dt}=r×m\frac{dv}{dt}+mv×\frac{dr}{dt}[/tex]

According to Wikipedia,

[tex]v=\frac{dr}{dt}[/tex]

[tex]mv×\frac{dr}{dt}=mv×v=0[/tex]

So [tex]\frac{dL}{dt}=r×m\frac{dv}{dt}=r×F=τ[/tex]

But isn't [tex]v=r\frac{dθ}{dt}≠\frac{dr}{dt}[/tex]

This is the part which bugs me. I hope someone can clarify it.

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