Collisions

N3 is for systems of 2 or more bodies. F1->2 =-F2->1. The force of object one on two is equal and opposite (vector speak for minus) of object two on one.
A collision is broken into three parts,

1. heading towards each other (N1),
2. touching, scrunching, and restoring (N3) and
3. heading out from each other (N1)

the collision dynamics, or how step 1 leads to step 3 is in the detail of step 2.

TIME - MOMENTUM

In the actual collision the body one and two feel equal but opposite forces for duration of time.

Considering each body (N2) we have F2->1. t = ma1.t for what happens to body 1

and F1->2. t = ma2.t. Use N3 and the formulae v-u =at to derive conservation of momentum (p)

p1= m1.v1. Conservation means momentum before = momentum after.

DISTANCE - Energy

The collision first through a scrunch deformation stage where KE is converted to mechanical deformation. If the mechanical deformation is springy or elastic, the mechanical deformation is PE (potential energy) that then explodes the particles appart. (PE restore KE).

So unlike momentum the direction matters, and the light object travels a greater distance, loosing more and gaining more KE. The maths is tricky so you will only deal with case of objects colliding and sticking together- Completely inellastic collisions.

Homework: Question 10 and 11 page 244 Jacaranda HSC science.