Dynamics · Physics

Equilibrium and Net Force

Equilibrium means ΣF = 0. Learn to solve stable systems and interpret “constant velocity” correctly.

This topic includes

Subtopics to master

Understand equilibrium, then solve real FBD + equation problems cleanly.

Equilibrium
Translational Equilibrium
If the net force is zero, acceleration is zero (rest or constant velocity).
  • ΣF = 0 meaning
  • a = 0 consequence
  • Graph interpretation
Start subtopicCore definition.
Types
Static vs Dynamic Equilibrium
Static: at rest. Dynamic: moving with constant velocity (still ΣF=0).
  • Rest case
  • Constant-velocity case
  • Misconceptions
Start subtopicSame ΣF rule.
Conditions
Conditions for Equilibrium
For translation in 2D: ΣFx=0 and ΣFy=0 (torque later in rotation).
  • Component equilibrium
  • Axis choice
  • Multiple unknowns
Start subtopic2D readiness.
Solve
Solving Equilibrium Problems
Draw an FBD, write ΣF equations, solve simultaneously for unknown forces.
  • FBD → equations
  • Algebra workflow
  • Check reasonableness
Start subtopicSystematic method.
Applied
Applications to Real Structures
Use equilibrium to analyze supports, hanging signs, and simplified structural systems.
  • Support forces (intro)
  • Tension in cables
  • Statics intuition
Start subtopicReal-world modeling.
Practice
Practice & Exercises
Equilibrium drills with FBDs, components, and solving for unknown forces.
  • ΣF=0 quick checks
  • Static/dynamic sorting
  • 2D equilibrium equation sets
  • Cables + supports problems
  • Exam-style multi-step statics
Open practiceConfidence builder.