key ideas and revision Physics

Key Concepts of Physics by Chapters 1. Physical Quantities, Units and Measurement • Memorize 7 base SI unites, prefixes • orders of magnitude e.g. Diameter of atom (10-10 m), Diameter of Earth (6 x 106 m) Refer to textbook • Use appropriate measuring apparatus (vernier calipers, micrometer screw gauge) • Pendulum experiment, measurement of diameters of circular objects • Vectors diagrams (vectors, resultant vectors), object in equilibrium (closed vector diagram) • Improve accuracy by taking more measurements at different points and finding the average, take timing for more oscillations 2. Kinematics • Describing of graphs (upward trend/downward trend/horizontal line (no change in y axis), straight line/curve) – at rest, constant, increasing, decreasing speed. Constant, increasing, decreasing acceleration and deceleration.) • Use of graphs (actual reading, gradient and area under the graph) • Always sketch the graph to solve problems. Do not use distance = speed X time (only constant speed) • Memorize definitions of distance, displacement, speed, velocity, acceleration, uniform speed/velocity, uniform acceleration and non-uniform acceleration. • Uniform = increase at a constant rate. • Free fall – an object in the air if without resistance will always be accelerating downwards with a value of g. • With air resistance, if moving up, then decreasing deceleration. If moving down, decreasing acceleration. (weight is constant, air resistance changes with speed. When speed is high, air resistance is high. Thus changing the resultant force. Resultant force is decreasing, hence acceleration is decreasing.) • With resistance, a falling body has an initial acceleration of 10m/s2 but experience decreasing acceleration. Weight is constant, but as speed increase, so is air resistance. Hence resultant force is decreasing. Decreasing till its weight = air resistance therefore terminal velocity. An object with a larger mass will have a higher terminal velocity as it experience greater acceleration before reaching terminal velocity. 3. Forces • Consider net force. Net force = 0, (moving at constant speed / at rest) • If there is a net force, then object moves with acceleration / deceleration. • Acceleration may be obtained from calculation or gradient of speed time graph. • Keywords – increasing, decreasing, constant acceleration, constant velocity and how it affects the resultant force. • Factors affecting friction – independent of surface area • Balanced force diagrams, free body diagrams – normal reaction force perpendicular to surface of contact, friction opposes direction of motion of surface in contact. 4. Mass, Weight and Density. • Definition and difference between mass and weight. Do not be ambiguous. E.g mass is constant, etc. • Define gravitational field strength g as gravitational force per unit mass N/kg. • Define inertia. Keywords = reluctance to change it state of rest of motion. • Convert betwee