- #1

- 2

- 0

## Main Question or Discussion Point

Trying to teach myself physics and I've run into a problem I don't quite understand.

"The magnitude of dA/dt can be found by the following geometrical argument. The change of A in the time interval t to Δt is"

Δ

And then somehow it gets to

|Δ

I just can't see how those are equal. Especially where theta/2 comes in.

This comes out of Kleppner pages 25 and 26, if that helps. Supposedly there's a sketch, but I can't see one.

"The magnitude of dA/dt can be found by the following geometrical argument. The change of A in the time interval t to Δt is"

Δ

**A**=**A**(t + Δt) -**A**(t)And then somehow it gets to

|Δ

**A**| = 2Asin(Δ[itex]\theta[/itex]/2)I just can't see how those are equal. Especially where theta/2 comes in.

This comes out of Kleppner pages 25 and 26, if that helps. Supposedly there's a sketch, but I can't see one.