AP Physics 1 · Unit 2, Part 1 · Forces

Newton’s First Law and Equilibrium

Test rest and steady motion, balance forces, and discover why moving at constant velocity does not require a net forward force.

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Learn by doing

Three ideas you’ll put into motion

Observe objects with zero net force while they are stationary or already moving.

Connect opposing force components with zero acceleration.

Use motion evidence to distinguish constant velocity from a change in velocity.

The big idea

Newton’s first law allows an object to remain at rest or continue at constant velocity when the net external force is zero.

Static equilibrium describes rest. Dynamic equilibrium can describe constant-velocity motion; individual forces may still be present.

A quick comparison

Compare a resting object with one moving steadily under zero net force.

Different velocities; the same zero acceleration.

Teaching this topic?Classroom fit, AP connections, and support

Classroom fit: Use for a concept introduction, guided independent practice, or a projected class discussion.
Before students begin: Force diagrams and the distinction between velocity and acceleration.
Built-in support: Prepared scenes, guided prompts, and feedback on lesson questions.
AP Physics 1 connections: Unit 2: Newton’s first law and translational equilibrium.
Check for understanding: Ask students whether a moving object with balanced forces must slow down, and why.
Optional extension: Use the Newton’s First Law experiment for an additional investigation.

The first scene is set up. Start the lesson and explore.