Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Define displacement, velocity, and acceleration.
• Distinguish between scalar and vector quantities.
• Calculate average speed and velocity.
• Solve problems involving uniform acceleration.
• Represent motion using graphs.

Lesson summary

This lesson explores projectile motion, which describes the path of an object thrown or launched into the air, moving only under the influence of gravity. This is a crucial concept in physics that builds upon our understanding of linear motion and vectors. Understanding projectile motion helps us analyze everything from a footballer kicking a ball at the Accra Sports Stadium, to a farmer spraying crops in the Volta Region, to the traditional game of 'ampe'. By breaking down this two-dimensional motion into its horizontal and vertical parts, we can predict the path, range, and flight time of any projectile.

Lesson notes

2.1 What is a Projectile?

A projectile is any object that is thrown, launched, or otherwise projected into the air and then moves under the sole influence of gravity. We make a key assumption in our calculations: we ignore air resistance. Examples: A kicked football, a stone thrown across a river, a javelin in athletics, water from a sprinkler. Not a projectile: A rocket with its engine firing, an aeroplane, a bird flying. (These have other forces acting on them, like thrust or lift).

The path followed by a projectile is a curve called a parabola. 2.2 The Principle of Independence of Motion

This is the most important concept for understanding projectiles. The motion of a projectile can be broken down into two separate and independent parts: Horizontal Motion (x-direction): There is no force acting horizontally (since we ignore air resistance). According to Newton's First Law, this means there is no horizontal acceleration (aₓ = 0). Therefore, the horizontal velocity (vₓ) is constant throughout the flight. Vertical Motion (y-direction): The force of gravity acts downwards. This causes a constant downward acceleration, which we call 'g' (acceleration due to gravity). We take upwards as the positive direction, so the vertical acceleration (aᵧ) is -g. (g ≈ 9.8 m/s² or 10 m/s² for calculations). The vertical velocity (vᵧ) changes continuously: it decreases as the object goes up, becomes zero at the maximum height, and increases in the downward direction. 2.3 Resolving Initial Velocity

Evaluation guide

• Explain the formation of the sun, planets and stars.
• Enquiry learning: Using the internet/reference books let learners research to come out with
• information on the formation of the sun, planets and stars.
• Challenge stereotypes and misconceptions about gender and disabilities in the study of space