IGCSE 0625 · MECHANICS · 1.1

Physical quantities & measurement

SI units, measuring length, volume, and time, careful technique, and the Extended idea of scalars and vectors. This is the foundation that every other measurement in the course rests on.

TOPIC 1.1: PHYSICAL QUANTITIES & MEASUREMENT CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON Numeracy & units LEADS TO 1.2 Motion 1.5 Forces Every measurement PHYSICAL QUANTITIES 1 · SI UNITS & QUANTITIES Every measured quantity has a number and a unit. Length is measured in metres (m). Mass is measured in kilograms (kg). Time is measured in seconds (s). Derived units are built from these: m/s for speed, kg/m³ for density. Prefixes scale a unit up or down: kilo (k) ×1000 milli (m) ÷1000 centi (c) ÷100 micro (µ) ÷1 000 000 2 · MEASURING LENGTH, VOLUME, TIME Length: a ruler; small widths with a micrometer or calipers. Liquid volume: a measuring cylinder, read at the bottom of the meniscus. Time: a stopwatch; a pendulum beats steadily. ruler cylinder 3 · MEASURING WELL Careful technique keeps errors small. Repeat a reading and take the average. Measure many together, then divide: time 20 swings of a pendulum, or measure a stack of 100 sheets of paper. Read scales straight on, with no gaps. measure the stack, divide by 100 4 · SCALARS & VECTORS EXTENDED A scalar has size only. A vector has size and a direction. Scalars: distance, speed, mass, time, energy. Vectors: displacement, velocity, acceleration, force, weight, momentum. Two perpendicular vectors combine by a scale drawing or Pythagoras: A B R
TOPIC 1.1: PHYSICAL QUANTITIES & MEASUREMENT CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON Numeracy & units LEADS TO 1.2 Motion 1.5 Forces Every measurement PHYSICAL QUANTITIES 1 · SI UNITS & QUANTITIES Every measured quantity has a number and a unit. Length is measured in metres (m). Mass is measured in kilograms (kg). Time is measured in seconds (s). Derived units are built from these: m/s for speed, kg/m³ for density. Prefixes scale a unit up or down: kilo (k) ×1000 milli (m) ÷1000 centi (c) ÷100 micro (µ) ÷1 000 000 2 · MEASURING LENGTH, VOLUME, TIME Length: a ruler; small widths with a micrometer or calipers. Liquid volume: a measuring cylinder, read at the bottom of the meniscus. Time: a stopwatch; a pendulum beats steadily. ruler cylinder 3 · MEASURING WELL Careful technique keeps errors small. Repeat a reading and take the average. Measure many together, then divide: time 20 swings of a pendulum, or measure a stack of 100 sheets of paper. Read scales straight on, with no gaps. measure the stack, divide by 100 4 · SCALARS & VECTORS EXTENDED A scalar has size only. A vector has size and a direction. Scalars: distance, speed, mass, time, energy. Vectors: displacement, velocity, acceleration, force, weight, momentum. Two perpendicular vectors combine by a scale drawing or Pythagoras: A B R
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