College Board-Aligned Original Notes
AP Physics 1: Algebra-Based Unit 2 Topic 4: Newton’s First Law
Newton's First Law connects balanced forces to constant velocity and identifies inertia as resistance to changes in motion.
Unit 2: Force and Translational Dynamics. College Board exam weighting listed for this unit: 18%-23% of multiple-choice exam score.
What to Know
- An object at rest remains at rest if the net force is zero.
- An object moving with constant velocity also has zero net force.
- Mass measures inertia, so larger mass means more resistance to acceleration.
- Always connect this topic back to the larger unit: Force and Translational Dynamics.
Detailed Notes
Newton’s First Law belongs to Unit 2: Force and Translational Dynamics. Newton's First Law connects balanced forces to constant velocity and identifies inertia as resistance to changes in motion. Start by naming the system, choosing axes or a sign convention when needed, and identifying which physical quantity is changing.
Key relationships: An object at rest remains at rest if the net force is zero. An object moving with constant velocity also has zero net force. Mass measures inertia, so larger mass means more resistance to acceleration.
Model to use: Compare a balanced free-body diagram with a motion description showing rest or constant velocity. A strong model should include labels, directions, units, and the reason each relationship applies.
AP-style move: If velocity is constant, the acceleration and net force are zero even when individual forces still act. For free-response work, write the principle first, show the setup, and then interpret the result in the physical context.
Key Vocabulary
Inertia
An object's resistance to changes in its motion.
Equilibrium
A state in which net force is zero.
Constant velocity
Motion with unchanged speed and direction.
Balanced forces
Forces whose vector sum is zero.
Static equilibrium
Equilibrium while the object remains at rest.
Quick Practice
How would you explain Newton’s First Law in one or two AP-style sentences?
Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.
Related Topics in This Unit
- Systems and center of mass
- Forces and free-body diagrams
- Newton’s Third Law
- Newton’s Second Law
Official Alignment
Reference and Attribution
AP Physics 1 concept reference: AP Physics 1: Concise Summary Notes by IITian Academy. EduCompanion used this source as a topic checklist and conceptual reference, then rewrote the study notes in original wording.