Lesson Notes By Weeks and Term v4 - SHS 2
DYNAMICS
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DYNAMICS
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 12
Grade code: 2.1.4.LI.2
Strand code: 1
Sub-strand code: 4
Content standard code: 2.1.4.CS.1
Indicator code: 2.1.4.LI.2
Theme: MECHANICS A ND MATTER
Subtheme: DYNAMICS
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Friction is a force that is all around us. It is the reason we can walk without slipping, why car brakes work, and why it is difficult to push a heavy wooden box across a rough concrete floor. In our daily lives in Ghana, from the grip of a trotro's tyres on a dusty road to the way we grind pepper in an "asanka" (earthenware bowl), friction is at play. In this lesson, we will explore this essential force, understand what causes it, and learn how to measure its effect through a hands-on experiment. Understanding friction is fundamental to understanding how and why objects move or stay still.
A. What is Friction?
Friction is a force that opposes the motion, or the tendency of motion, between two surfaces in contact. Imagine pushing a heavy bag of charcoal across the floor. You feel a resistance. That resistance is friction. Friction always acts in the direction *opposite* to the direction of motion or intended motion.
B. Types of Friction
There are two main types of friction we will study: Static Friction (Fs): This is the frictional force that exists between two surfaces when there is *no relative motion*. It prevents an object from starting to move. Key Idea: Static friction is a *variable* force. It increases as you apply more force, up to a certain maximum value. Limiting Static Friction (Fs, max): This is the *maximum* value of static friction that must be overcome to start the motion. Once your applied force exceeds this value, the object will start to move. Kinetic (or Dynamic) Friction (Fk): This is the frictional force that exists between two surfaces when they are *sliding* against each other. Key Idea: Kinetic friction is generally *constant* for a given pair of surfaces, as long as the object is moving. Important Note: The kinetic friction (Fk) is usually *less than* the limiting static friction (Fs, max). This is why it is often harder to *start* pushing a heavy object than it is to *keep it moving*.