Measurement

• A physical quantity is a scientifically measurable quantity that consist of a numerical value and a unit.
• The base quantities are the seven physical quantities of the SI system by which all other physical quantities are defined.
• The seven base quanities consists of length { metre ; m }, mass { kilogram ; kg }, time { second ; s }, electric current { ampere ; A }, thermodynamic temperature { kelvin ; K }, luminous intensity { candela ; cd } and amount of substance { mole ; mol }. (Hint: base quanitity { SI unit ; Symbol })
• Base units are the seven units of the SI system, related to the base quantities, whose magnitude is defined without referring to other units.
• Derived units are units that are derived from base units and can be expressed in terms of products and quotients of base units.
• Derived quantities are physical quantities that are derived from base quantities and can be expressed in terms of products and quotients of base quantities.
• What are the derived units of Force (N)?

  kg m s^-2
• What are the derived units of Energy (J)?

  kg m^2 s^-2
• What are the derived units of Power (W)?

  kg m^2 s^-3
• An equation is homogenous if the base units of all the terms in the equation are the same.
• What's the prefix used for the unit measurement of 10^-12?

  pico
• What's the prefix used for the unit measurement of 10^-9?

  nano
• What's the prefix used for the unit measurement of 10^-6?

  micro
• What's the prefix used for the unit measurement of 10^-3?

  milli
• What's the prefix used for the unit measurement of 10^-2?

  centi
• What's the prefix used for the unit measurement of 10^-1?

  deci
• What's the prefix used for the unit measurement of 10^3?

  kilo
• What's the prefix used for the unit measurement of 10^6?

  mega
• What's the prefix used for the unit measurement of 10^9?

  giga
• What's the prefix used for the unit measurement of 10^12?


  tera
• What is the estimated mass of a ping pong ball (in kg)?

  0.003 kg
• What is the estimated mass of an apple (in kg)?

  0.2 kg
• What is the estimated mass of a human male (in kg)?

  70 kg
• What is the estimated mass of the Earth (in kg)?

  6x10^24 kg
• What is the estimated diameter of hair (in m)?

  0.0002 m
• What is the estimated length of a football field (in m)?

  100 m
• What is the estimated radius of the Earth (in m)?

  6x10^6 m
• What is the estimated speed of the fastest runner (in m s^-1)?

  10 m s^-1
• What is the estimated speed of sound (in m s^-1)?

  330 m s^-1
• What is the estimated speed of light (in m s^-1)?


  3x10^8 m s^-1
• Scalar is a quantity that has magnitude, not direction. It is completely specified by its numerical value and unit.
• Vector is a quantity having both magnitude and direction. It must be specified with its value, unit and direction.
• Uncertainty is the range of values on both sides of a measurement in which the actual value of the measurement is expected to lie.
• Uncertainties in measured quantities arise from:

  • Limitations of the observer
  • Limitations of the measuring instrument used
  • Limitations of the method used
• Error is the difference between the measured value and the true value.
• Systematic errors are present when the measured values produced errors of the same magnitude and sign.
• Examples of Systematic Errors:

  • Due to apparatus
  • Due to poor experimental techniques
  • Due to external factors
• Random errors are present when the measured values produced errors of different magnitudes and signs. These readings are scattered about the mean value with no fixed pattern.
• Examples of Random Errors:

  • Due to inability of observer to repeat his action precisely
  • Due to environmental conditions
  • Due to the limited sensitivity of instruments
• The precision of a measurement is how close the experimental value are to each other.