Physics Forces and Newton’s Laws: Free-Body Diagrams, Weight, and Motion

Force

A push or pull on an object.

System

An object or group of objects being studied.

Free-Body Diagram

A drawing showing all external forces acting on an object.

Net Force

The vector sum of all forces acting on an object.

Newton's Second Law

Acceleration equals net force divided by mass (a = F/m).

Newton's First Law

An object maintains its velocity unless acted on by a net force.

Inertia

The tendency of an object to resist changes in its motion.

Equilibrium

When the net force on an object is zero.

Weight

The gravitational force acting on an object.

Gravitational Field

A region where an object experiences gravitational force.

Apparent Weight

The support force exerted on an object, often measured by a scale.

Weightlessness

When an object's apparent weight is zero.

Drag Force

A fluid force opposing an object's motion.

Terminal Velocity

Constant velocity reached when drag balances other forces.

Interaction Pair

Equal and opposite forces acting on two different objects.

Newton's Third Law

For every action force, there is an equal and opposite reaction force.

Tension

The pulling force transmitted through a rope, string, or cable.

Normal Force

The perpendicular contact force exerted by a surface.