Lesson 2: Investigating Force and Motion

Key Idea

Moving from observation to formal physics, a force is strictly defined as a push or a pull resulting from an interaction between two objects. A force cannot exist on its own; it requires a source and a receiver.

Whenever this interaction occurs, it dictates a change in velocity. This definition removes ambiguity: if velocity changes (acceleration, deceleration, or turning), a force is definitively acting. If velocity is constant, no net force is interacting with the object. This scientific definition provides the rulebook for solving the unit's mystery.

Key Idea

Objects possess a natural tendency to resist changes to their state of motion.

A soccer ball on a field remains stationary until kicked. Similarly, a satellite gliding through deep space continues at a constant speed forever unless a thruster fires or gravity acts upon it.