Lesson Notes By Weeks and Term v4 - SHS 2
KINEMATICS
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KINEMATICS
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 10
Grade code: 2.1.3.LI.3
Strand code: 1
Sub-strand code: 3
Content standard code: 2.1.3.CS.1
Indicator code: 2.1.3.LI.3
Theme: MECHANICS AND MATTER
Subtheme: KINEMATICS
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This lesson explores the physics behind a common experience for every Ghanaian: travelling in a vehicle around a bend or a roundabout. We see tro-tros, taxis, and motorbikes navigate curves every day, from the roundabouts in our local towns to major interchanges like the Tetteh Quarshie Interchange in Accra. Why do some vehicles skid, especially on rainy days? And how do road engineers design curves on highways like the Accra-Tema motorway to make them safer? We will investigate the forces at play when an object moves in a circle, focusing on the problem of skidding and the engineering solution of banking roads.
Part 1: The Problem – Skidding on a Flat Curve
Imagine a car or a tro-tro turning at a roundabout on a flat road. To follow a curved path, an object must have a net force acting on it that is directed towards the centre of the circle. This net force is called the centripetal force (Fc). Key Question: On a flat, horizontal road, what force provides this necessary centripetal force? Answer: The force of static friction (fs) between the vehicle's tyres and the road surface. This friction acts horizontally, pointing towards the centre of the curve.
From Newton's Second Law applied to circular motion, the required centripetal force is: `Fc = mv² / r` where: `m` = mass of the vehicle `v` = speed of the vehicle `r` = radius of the curve
The maximum static friction available is given by `fs(max) = μs * N`, where `μs` is the coefficient of static friction and `N` is the normal reaction force. On a flat road, `N = mg`. So, `fs(max) = μs * mg`.