For collision, physical contact is not a necessary condition. Why?

In science, language is specific and unambiguous. That means that terms are defined in ways often different from colloquial usage.

I'll quote Wikipedia on the definition of a collision. "A collision is an event in which two or more bodies exert forces on each other for a relatively short time." Note that there is no requirement for contact.

Of the four fundamental forces, both electromagnetism and gravity are long range. Despite being long range, they both fall with the inverse square of the distance (for simply distributed objects). This means you can mostly ignore the effects of the force at large distances relative to their closest approach.

A charged particle being deflected by another charged particle as they pass by each other is an example of a collision where no contact takes place. A gravitational slingshot where a small object moves around a much heavier object to gain speed is another example.

This may be a somewhat pedantic answer, but I think for the purposes of cultivating clear language, I'd call into question the notion of "physical contact" as implied by the textbook's usage of the word and instead answer as follows: If the "collision" of two or more relatively moving bodies (as it implies) means a mutually wrought-on-one-another change of motion state, then there has been physical contact, by definition. There has been exchange of momentum and or angular momentum and energy by dint of some interaction.

When we say "physical contact" colloquially, we mean a particularly strong interaction wrought by particularly tight nearness of the two bodies to one another, with a cluster of results that evokes our intuitive idea of "physical contact", such as: triggering of the sense of touch, if one of the bodies is a sentient animal, sharp deformation and possibly fracture of some of the bodies at their points of nearest approach, permanent, plastic deformation such as scratching, scoring or warping and clearly hearable "contact" sounds. But, at the most basic level, such an interaction is different from any other interaction through the four basic forces of nature only through the strength of the interaction. There's no real fundamental qualitative difference at all: when we "touch" a body, we're simply feeling the deformations of our own body wrought by fundamental forces - electromagnetism - between our bodies and what we're touching. Whether we're feeling the Coulombic repulsion between our finger and the atoms of the table it is resting on, or the Coulombic repulsion between the charged ball we are holding and a like charged one several centimeters from "physical contact" with the former, there's nothing really different that is happenning at a fundamental level.

When trying to define what makes "physical contact" different from other interactions, we quickly discover there is no rigorous definition that will differentiate it from other interactions.

All scatterings are examples of collisions. You may consider the example of Rutherford's alpha scattering in which there is no physical contact between alpha particle and the nucleus.