Dynamics · Physics

Types of Forces

Recognize forces by interaction type so your free-body diagrams are always complete.

This topic includes

Subtopics to master

Learn the common force models used throughout introductory mechanics.

Gravity
Gravitational Force Near Earth
Model weight as a downward force of magnitude mg near Earth’s surface.
  • Direction and point of action
  • When mg is valid
  • Link to free fall
Start subtopicMost common force.
Contact
Normal Force and Surface Contact
The normal force is perpendicular to the contact surface (not always equal to mg!).
  • Perpendicular by definition
  • Normal adjusts to situation
  • Inclines + acceleration cases
Start subtopicDon’t assume N=mg.
Ropes
Tension in Ropes and Cables
Tension pulls along the rope; ideal ropes transmit the same tension through segments.
  • Direction along rope
  • Ideal string assumptions
  • Multiple segments
Start subtopicPreps pulleys.
Friction
Static and Kinetic Friction
Friction acts parallel to the surface and opposes relative motion (or its tendency).
  • Static vs kinetic
  • Direction logic
  • μ models
Start subtopicHuge exam topic.
Fluids
Drag and Air Resistance (Conceptual)
Drag depends on speed and shape; it usually opposes motion through a fluid.
  • Opposes relative motion
  • Speed dependence (qualitative)
  • Terminal velocity idea
Start subtopicKeep it conceptual.
Practice
Practice & Exercises
Force-identification drills and FBD mini sets using all force types.
  • Identify forces by interaction
  • Normal/tension direction drills
  • Friction direction reasoning
  • Mixed scenario FBDs
  • Short explanation questions
Open practiceRecognition → mastery.