Physics notes and concept map

Length, volume and time Prefixes: nano (10-9), micro (10-6), milli ( 10-3), kilo(103), Mega(106), Giga (10 9). Degree of accuracy of instruments: Metre rule and measuring tape (0.1 cm), Vernier calipers (0.01 cm), Micrometer (0.01 mm). Types of errors: Zero error, parallax error Mass vs Weight mass is a measure of the amount of substance in a body BUT weight is a measure of gravitational force on a mass W = m g electronic balance: mass (kilogram, kg) spring balance: force/weight (newton, N) Mass remains constant but weight can change because of acceleration due to gravity. Density is mass per unit volume D = m / V (SI Units: kg/m3 ) Density of water is 1 g/cm3 or 1 000 kg/m3) Less dense (lower density): float Denser (higher density): sink Speed and acceleration Speed is the rate of distance travelled S = D/t Acceleration is the rate of change of velocity a = (v-u)/t (Unit: m/s2) Average speed = total distance / total time or = (u + v) / 2 Speed-time graph: gradient = acceleration, area under graph = distance Distance-time graph: gradient = speed MECHANICS Forces F = m a Resultant force = 0 when (i) object is at rest or (ii) object is at constant speed Zero resultant force means that the forces are opposite and equal. Eg. friction = forward force, weight = air resistance. Vector drawing Note: choose an appropriate scale, state both resultant force and direction. Single arrow for forces but double arrow for resultant force. For drawing of parallelogram, all forces point away from the same starting point. Tracing of lines in dotted lines. Centre of gravity It is the point where the whole weight seems to act. For a body to be stable, base area of object must be large and its CG is low. The line of weight through the CG must lie within the base area of the object. Energy is the capacity to do work. (Unit: Joule) Energy stores: chemical potential, kinetic, gravitational potential, elastic potential, internal, nuclear. Methods of transfer: by heating, mechanically, electrically, by propagation of electromagnetic waves/ sound waves. Energy cannot be created or destroyed, but can be transferred from one store to another. The total amount of energy in an isolated system remains constant. Work, energy and power Work done is the product of the magnitude of a force and the distance moved in the direction of the force (Unit: Joule) W = F x // d Formulas of energy: - Kinetic = ½ mv2 - Gravitational Potential = mgh Power is the rate of doing work.(Unit: Watts) Power = Energy / time or Work / time P = E / t or P = W / t Scalar & Vector Scalar quantity is a quantity that has magnitude only. Eg. mass, speed, distnace. Vector is a quantity that has both magnitude and a direction. Eg. force, velocity, acceleration, weight, displacement. Turning effect of Forces Moment is the product of a force and its perpendicular distance from the pivot to the line of action of the force. (Unit: Nm or Ncm) Mom