Measurement - U1

• Physical quantity

  One which has both magnitude and a unit
• Physical quantities

  • Length
  • Mass
  • Time
  • Temperature
  • Area
  • Volume
• Length

  Straight line distance between 2 points
• Measurement of length

  • Short lengths can be measured by using rulers and vernier callipers
  • Long lengths can be measured by using metre-rule, measuring tape, trundle wheel, etc...
• Conversion of units

  1. 1m = 100 cm

  2. 1 cm = 10 mm

  3. 1m = 1000 mm

  4. 1 km = 1000 m
• Parallax error

  Occurs when the line of sight of observer is not perpendicular to scale
• To avoid parallax error

  The line of sight must be just opposite and perpendicular to the mark being read
• Zero error

  Occurs when a measurement does not start from zero
• Volume

  The amount of space occupied by a body

  SI unit is m^3
• Measurement of volume

  1. 1m³ = 1,000,000 cm³

  2. 1L = 100 cL

  3. 1L = 1000 ml

  4. 1ml = 1 cm³

  5. 1L = 1000 cm³
• Displacement method to measure volume

  1. Measuring cylinder is partially filled with water

  2. Initial level V1 of water is recorded

  3. Object is tied with thin thread and lowered into water

  4. New level V2 of water is recorded

  5. Volume of object = Difference in volume
• Precautions for displacement method

  • Measuring cylinder must be on flat levelled surface
  • Avoid parallax error when reading scale
  • Lower object gently to avoid splashing
  • Thread must be thin so its volume is negligible
• Displacement can to measure volume

  1. Displacement can is filled up to spout level

  2. Object is tied with thin thread and completely immersed in water

  3. Displaced water overflows through spout into measuring cylinder

  4. Volume of object = Volume of water collected
• Volume of liquid can be measured using a measuring cylinder
• Meniscus is the curved surface of liquid
• Mass

  The amount of matter a substance contains
• SI unit for mass

  • Kilogram (kg)
• Instruments used to measure mass

  • Balance
  • Beam balance
  • Top-pan compression balance
  • Lever balance
  • Electronic balance
• Conversion of mass units

  1. 1kg = 1000 g

  2. 1 g = 1000 mg

  3. 1 tonne = 1000kg
• Time

  A measure of the duration of an event
• SI unit for time

  • Second (s)
• Instruments used to measure time

  • Watches
  • Analogue
  • Digital
  • Clocks
  • Stop watches
  • Electronic timer
  • Pendulum
• Conversion of time units

  1. 1min = 60 s

  2. 1h = 60 min

  3. 1day = 24 h

  4. 1week = 7 days

  5. 1year = 365 days
• Simple pendulum

  • Consists of an object (bob) suspended by a string (thread) about a support
• Periodic time

  The time taken for one complete oscillation
• The periodic time is independent of the mass of the bob, but dependent on the length of the pendulum
• Experiment to measure periodic time of a simple pendulum

  1. Measure time t1 for 20 oscillations

  2. Measure time t2 for another 20 oscillations

  3. Calculate average time tav = (t1 + t2)/2

  4. Periodic time T = tav/20
• Temperature

  The degree of hotness or coldness of a substance
• SI unit for temperature

  • Kelvin (K)
• Types of thermometers

  • Liquid-in-glass
  • Digital
• Liquid-in-glass thermometer

  • Uses mercury or alcohol as the thermometric liquid
  • Range of school laboratory thermometer is -10°C to 100°C
• Clinical thermometer

  • Used to measure human body temperature
  • Range is 35°C to 42°C
  • Has a constriction to prevent mercury from flowing back into the bulb
  • Before using, it has to be shaken
• The human body temperature of a healthy person is about 37°C