Differences in velocity conceptual question

[Pochen Liu]

Homework Statement

If I want to find the difference in velocities of 2 objects A and B
We know the sum of their velocities is A + B
But but is the difference B - A
Why not A - B?

Homework Equations

This is from the equation of calculating restitution where
(greek letter) = (The difference in the velocities after the collision)/(Difference in the velocities before the collision)

The Attempt at a Solution

N/A other than google which didnt help.

 

[Chandra Prayaga]

Your equation for the coefficient of restitution (if that is what you mean bt restitution) is not quite right. For collisions in one dimension, It is:
e = (v_B - v_A) / (u_A - u_B), where the v's denote velocities after collision and the u's denote velocities before collision. Note the reversal in order of A and B between numerator and denominator.
In two and three dimensions, you define the coefficient of restitution in terms of the components of the velocities along the line of impact.

 

[Pochen Liu]

Ok, see I literally copy and pasted the schools scholarship 'formulae' in here. Good to know the equation actually specifies it in constants.