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Newton's Laws Cheat Sheet

The core ideas of Newton's Laws distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Inertia (First Law)

An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by a net external force.

Net Force and Acceleration (Second Law)

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass, expressed as F = ma.

Action-Reaction Pairs (Third Law)

For every action force, there is an equal and opposite reaction force. These forces act on different objects simultaneously.

Net Force

The vector sum of all forces acting on an object. When net force is zero, the object is in equilibrium and does not accelerate.

Free-Body Diagram

A simplified drawing that shows all the forces acting on a single object as arrows pointing in the direction each force is applied.

Mass versus Weight

Mass is the intrinsic quantity of matter in an object (measured in kg) and does not change with location. Weight is the gravitational force on that mass (W = mg) and varies with the local gravitational field strength.

Equilibrium

A state in which the net force on an object is zero. Static equilibrium means the object is at rest; dynamic equilibrium means it moves at constant velocity.

Normal Force

The perpendicular contact force exerted by a surface on an object. It adjusts in magnitude to prevent objects from passing through surfaces and plays a key role in friction calculations.

Key Terms at a Glance

Inertia:The tendency of an object to resist changes in its state of motion. Mass is the quantitative measure of inertia.
Net Force:The vector sum of all forces acting on an object. A nonzero net force causes acceleration according to F = ma.
Mass:A scalar quantity measuring the amount of matter in an object and its resistance to acceleration. Measured in kilograms (kg).
Weight:The gravitational force acting on an object, equal to mass times local gravitational acceleration (W = mg). Measured in newtons (N).
Normal Force:The perpendicular contact force exerted by a surface on an object resting on it, preventing the object from passing through the surface.
Free-Body Diagram:A diagram showing a single object with arrows representing all external forces acting on it, used to analyze the net force and resulting acceleration.
Equilibrium:A condition where the net force on an object is zero, resulting in zero acceleration. Can be static (at rest) or dynamic (constant velocity).
Newton (unit):The SI unit of force. One newton is the force required to accelerate a one-kilogram mass at one meter per second squared (1 N = 1 kg*m/s^2).
Action-Reaction Pair:Two forces described by Newton's third law that are equal in magnitude, opposite in direction, and act on two different objects simultaneously.
Acceleration:The rate of change of velocity with respect to time, measured in m/s^2. Caused by a nonzero net force according to Newton's second law.
Tension:The pulling force transmitted through a string, rope, cable, or similar connector, directed along its length away from the object.
Applied Force:A contact force exerted on an object by a person or another object through direct physical interaction, such as pushing or pulling.

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Newton's Laws Cheat Sheet - Quick Reference Guide | PiqCue