"Collisions" do not simply refer to objects that come into contact with one another.  Rather, collisions can refer to objects that interact via a non-contact force such as an electrostatic force or gravitational force.  Galaxies passing one another interact and can be referred to as colliding.

Set values for the initial position, velocity, and mass of the two particles, and click on the button "Initialize Animation" to play the animation using your specified values.  Note, if m or v are too large, the particles may actually pass through one another which will seem a little strange.  Note: the interaction between the particles is a "non-contact" interaction, much like the electrostatic force on two charges.  Mathematically, it is actually a Hooke's law interaction.

 

Blue particle Red particle
mblue=kg mred=kg
vblue=cm/s vred=cm/s
xblue=cm xred=cm