Lesson 5: Uniform Circular Motion & Centripetal Force
Demonstrating understanding of mechanical principles, motion, forces, and energy for NCEA Level 2 Physics.
🎯 Ngā Whāinga Akoranga | Learning Intentions
Uniform circular motion speed (v = 2 pi r / T), centripetal acceleration (a_c = v^2 / r directed inward), and centripetal force (F_c = m v^2 / r).
Calculate centripetal acceleration and net inward force for vehicles rounding horizontal curves, satellites in orbit, and banked tracks.
🎥 Media Anchor & Pedagogical Scaffold
Uniform Circular Motion & Centripetal Force
Video Clip: Circular motion and centripetal force — IGCSE physics with worked examples (Runtime: 10m 49s).
🧠 1. Before Viewing (Activate & Predict)
Why does an object moving at constant speed in a circle experience continuous acceleration toward the centre?
👁️ 2. During Viewing (Watch With a Job)
- Direction: in circular motion, which direction does the centripetal force always point? Draw a diagram to illustrate.
- Formula: write the centripetal force equation F = mv²/r. Identify what each variable represents and its SI unit.
- Apply: a 2 kg object moves in a circle of radius 0.5 m at 3 m/s. Calculate the centripetal force. Show every step.
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Whirl a bucket of water overhead to demonstrate normal force and minimum critical speed at top of loop.
Immediate Task: Complete Section 5 of your Mechanics Portfolio: Centripetal Force Calculations & Banked Track Physics.
⚡ Whakaoho | Do Now: Physics Mechanics Recall (10 mins)
There is no outward force on you in a turning car. You feel thrown outward. Nothing is pushing you that way.
Two minutes: name what is actually happening to your body (inertia — you continue straight), and identify the real force acting on the car, its direction, and where it comes from. Then say what happens the instant that force is removed on a wet corner. The car does not fly outward; it goes straight.
📖 Activity 1: Mechanical Investigation & Vector Problem Solving (25 mins)
Calculate the requirement (15 min). For a car on three corner radii at three speeds, calculate the centripetal force required. Note what doubling the speed does to that requirement — the v² is the whole reason speed limits tighten on bends.
Where does it come from? (10 min). For four scenarios — car on a road, ball on a string, satellite, rider in a loop — name the physical force supplying the centripetal requirement in each. It is a different force every time; centripetal is a job, not a kind of force.
📝 Activity 2: Level 2 Physics Portfolio Task & Merit/Excellence Scaffolding (20 mins)
Portfolio — Section 5. Submit: (1) nine centripetal force calculations tabulated with the v² relationship stated; (2) four scenarios with the supplying force named in each; (3) a paragraph correcting the 'outward force' misconception using inertia.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 2 Alignment: Direct preparation for Level 2 Physics (Demonstrate understanding of mechanics). Emphasise linking mathematical working directly to physical concept explanations for Merit/Excellence grades.