[McCoy]

hi folks, apologies first because I don't have the diagram for what I'm talking about here. In atkin 8th edition page 872 , and 9th edition page 834. The authors talk about two colliding molecules, A and B.  "Relative velocity (vrel,A-B) is the magnitude of the relative velocity component parallel to an axis that contains the vector connecting the centres of A and B". Vrel is the relative velocity of  A and B after collision (i guess?) and it makes angle theta with the vrel,A-B (both have their origin at A)....and A is the larger molecule. d is the distance between the two centres and 'a' is the distance connecting the centre of molecule A with the vrel.

In 9th editiion, the authors claim vrel,A-B = vrel/cos (theta) (no problem) = vrel [(d^2-a^2)/d^2]^1/2 (how?). In my calculation, cos (theta) = [(d^2-a^2)/d^2]^1/2 and hence d^2 is the numerator.

In 8th edition, the equation is the same as above, but instead of having division between vrel and cos(theta)...they have a multiplication. This is a serious issue...one has to be wrong...or they are both wrong anyway because I don't think there's a way .vrel,A-B would be equal to vrel*cos (theta) or am I missing something?
I really need your help. My description is not really clear, sorry about that.
Thank you.

[McCoy]

*Ignore me, I am impatient*

[McCoy]

Finally>diagram.


Thanks fellows.

Edit: I forgot to mention that this in the 9th edition Atkin PCHEM.

[McCoy]

okay don't worry...I got helped somewhere. Cheers.