Lesson Notes By Weeks and Term v4 - SHS 3
KINEMATICS
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KINEMATICS
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Subject: Physics
Class: SHS 3
Term: 1st Term
Week: 10
Grade code: 3.1.1.LI.2
Strand code: 1
Sub-strand code: 2
Content standard code: 3.1.1.CS.3
Indicator code: 3.1.1.LI.2
Theme: MECHANICS AND MATTER
Subtheme: KINEMATICS
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This lesson bridges the gap between the formal study of motion (Kinematics) and the ancient wisdom of our ancestors. We often apply kinematic principles to cars, falling objects, and projectiles. However, the most magnificent examples of motion occur in the heavens above us. For thousands of years, before telescopes and modern physics, Ghanaians and other indigenous peoples were expert astronomers. They observed the predictable motion of the Sun, Moon, and stars—the very essence of kinematics—to navigate, farm, tell time, and structure their societies. This lesson will show that kinematics is not just a classroom topic; it is a fundamental tool that has shaped our culture and survival.
Part A: A Quick Review of Kinematics
Kinematics is the branch of mechanics that describes the motion of objects without considering the forces that cause the motion. Displacement (s): The change in position of an object. It is a vector quantity. For a planet, its displacement over one full orbit is zero, but the distance travelled is the circumference of the orbit. Velocity (v): The rate of change of displacement. It is also a vector. For celestial bodies in a stable orbit, we often talk about orbital speed, which is the magnitude of the velocity. Acceleration (a): The rate of change of velocity. An object moving in a circle (like a planet in a near-circular orbit) is always accelerating towards the centre of the circle. This is called centripetal acceleration. Part B: The Kinematics of Celestial Motion
The sky is a giant laboratory for observing kinematics. The key motions are rotation and revolution. Apparent Daily Motion: From our perspective on Earth, the Sun, Moon, and stars appear to move across the sky from East to West. This is a direct result of the Earth's rotation on its axis. The kinematics here is about relative velocity. The celestial objects are not actually circling us daily; we are spinning. Orbital Motion (Revolution): Planets revolve around the Sun, and the Moon revolves around the Earth. We can describe this using kinematics. For a simplified circular orbit: Orbital Period (T): The time taken to complete one full revolution. (e.g., for Earth around the Sun, T ≈ 365.25 days). Orbital Radius (r): The average distance from the centre of the orbit. Orbital Speed (v): The speed of the object as it moves along its orbit. Since speed = distance/time, for one full orbit: Distance = Circumference = 2πr Time = Orbital Period = T Therefore, v = 2πr / T