Which principle asserts that contact between two objects results in an exchange of trace material?

Locard's principle of exchange is a fundamental concept in forensic science which states that whenever two objects come into contact with one another, there is an exchange of trace material between them. This principle underscores the idea that any interaction can leave behind evidence that can be crucial for investigations, such as fibers, hair, or fingerprints.

This principle is particularly significant in criminal investigations, where the presence or absence of trace evidence can help build a case or refute claims made by suspects. Locard's assertion is foundational in establishing the link between a suspect and a crime scene based on the materials transferred during contact.

The other options, while relevant in their own contexts, do not address the concept of trace material exchange between objects. Newton's third law deals with the action and reaction forces, Watson's theory pertains to scientific observations and their interpretations, and Hume's principle focuses on relationships between cause and effect, none of which relate directly to the exchange of trace evidence in forensic contexts.