KINEMATICS Objectives • define and use: -distance -displacement -speed -velocity -acceleration. What is kinematics? • It is the study of motion of bodies without consideration of the forces involved. Distance • Refers to how much ground an object has covered during its motion. • The SI unit of distance is the metre (m). Displacement • It is the distance moved in a specific direction. • The SI unit of displacement is the metre (m). Scalar or Vector quantity? • Distance (Scalar quantity) • Displacement (Vector quantity) Example Example • Consider a car travelling in a straight line from point A to B, then back to point A and further to point C. • Calculate: • a) Distance travelled from A to B and back to A [Ans: 12m] • b) Displacement for the motion described in (a) [Ans: 0m] • c) Distance from A to B then to C [Ans: 16m] • d) Displacement for the motion described in (c) [Ans: -10m] Speed • It is distance travelled per unit time. • Or the rate of change of distance. • SI unit: ms-1 a) Average Speed • It is the total distance travelled by an object divided by the total time taken. • Average speed = 𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 b) Instantaneous Speed • It is the speed of an object at a particular moment in time. • If you look at the speedometer in a car, it doesn’t tell you the car’s average speed; rather, it tells you its speed at the instant when you look at it. This is the car’s instantaneous speed. • Instantaneous speed will be equal to the average speed only if the body moves with a uniform speed throughout. Velocity • It is the rate of change of displacement. • The velocity of an object can be thought of as its speed in a particular direction. • SI unit: ms-1 Scalar or Vector? • Speed (Scalar quantity) • Velocity (Vector quantity) Example Solutions a) Average Speed = 0.50m/s b) Average Velocity = 0 m/s Standard symbols and units Acceleration • It is the rate of change of velocity • Acceleration is a vector quantity. • Word equation: • Acceleration = • SI unit: ms-2 𝑐ℎ𝑎𝑛𝑔𝑒 𝑜𝑓 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑡𝑖𝑚𝑒 Example Solution a) Time = 24s b) Acceleration = -5.0 ms-2 Tasks • 1. An airplane flies with a constant speed of 800 km/h. How far can it travel in 75 minutes? • 2. Abigail travels in an airplane a distance of 1440 km. For one-third of the distance, the airplane flies at a speed of 640 km/h, and for the rest of the distance, it flies at a speed of 680 km/h. How long does the trip take? • 3. State and explain whether an object moving in a circle at constant speed is accelerating. • 4. A car accelerates uniformly from a speed of 20ms-1 to a speed of 25ms-1 in 2s. Calculate a. the average speed for this period of 2s b. the distance travelled during this period c. the acceleration
