Lesson 2.9 • Competency 2.6Complete Lesson
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Uniform Circular Motion

Angular kinematics (θ, ω), centripetal acceleration (a = v²/r = ω²r), centripetal force, banked roads, conical pendulum, and vertical circular motion.

Marking a lesson complete represents finishing your study of the topic; it does not denote tested mastery.

Learning Objectives

  • Relate linear velocity to angular velocity (v = rω) and centripetal acceleration (a = v²/r).
  • Analyze banking angle conditions on curved roads (tan θ = v² / rg) and critical speed in a vertical loop.

Core Theory & Concepts

An object moving along a circular path of radius r at constant speed v experiences continuous inward directional change. This centripetal acceleration requires a real net inward centripetal force to sustain rotation.

Centripetal Acceleration & Force

Acceleration is directed towards the circle center: a_c = v² / r = ω² r. Centripetal force: F_c = m v² / r = m ω² r.

F_c = m v² / r = m ω² r

Banking of Curved Roads

To prevent vehicles skidding without relying on tire friction, roads are banked at angle θ: tan θ = v² / (rg).

tan θ = v² / (rg)

Common Misconceptions

Misconception

Treating "centrifugal force" as a real physical force acting on an object in an inertial frame.

Physical Clarification:In an inertial frame of reference, only the inward centripetal force exists. Centrifugal force is a fictitious pseudo-force that arises only in the rotating non-inertial reference frame.

Syllabus Topic Outline

Competency 2.6
  • 1Angular displacement θ and angular speed ω = dθ/dt
  • 2Centripetal acceleration derivation a_c = v²/r = ω²r
  • 3Banked roadway design for friction-free curving: tan θ = v²/rg
  • 4Motion in a vertical circle: critical apex speed v_min = √(gr)

Practice Problems

1

A stone tied to a string of length 0.9 m rotates in a vertical circle. Taking g = 10 m s⁻², what is the critical minimum speed in m s⁻¹ at the highest point?