Dynamics · Physics

Forces and Interactions

Understand force as an interaction, identify the system, and learn the diagrams that power Newton’s-law problem solving.

This topic includes

Subtopics to master

These set up every Newton’s-law problem you’ll ever solve.

Concept

Force as an Interaction Between Objects

Forces don’t exist alone — they arise from interactions.

Classification

Contact vs Non-Contact Forces

Recognize which forces require physical contact and which do not.

Setup

Identifying Interacting Objects

List what interacts with your object to list all possible forces.

Modeling

System vs Surroundings

Define your system so you know which forces are external vs internal.

Diagrams

Force Diagrams vs Free-Body Diagrams

Two diagram styles: one shows interactions, the other isolates one object’s forces.

Practice

Practice & Exercises

Train the fundamentals: identify interactions, systems, and forces quickly and correctly.