Dynamics · Physics

Newton’s First Law (Inertia)

Build the correct intuition: if the net force is zero, motion doesn’t “need” a force to keep going.

This topic includes

Subtopics to master

Learn what inertia really means, and eliminate the most common misconceptions about motion.

Core idea

Concept of Inertia

Inertia is resistance to changes in motion (and it’s tied to mass).

Frames

Inertial Reference Frames

Newton’s laws are simplest in non-accelerating frames.

Result

Motion with Zero Net Force

If ΣF = 0, velocity is constant (could be zero or nonzero).

Pitfalls

Common Misconceptions About Motion

Common errors: “force needed to keep moving,” “motion implies force,” etc.

Examples

Real-World Examples

Connect the law to coasting, stopping, and sliding situations.

Practice

Practice & Exercises

Concept checks and quick reasoning problems for ΣF = 0 scenarios.