Subjective measurement

Examples of Subjective measurement in the following topics:

• Quality of Sound

  • It can be measured objectively or subjectively.
  • Objective measurement is taken when tools are used to gauge accuracy.
  • Subjective measurement is more of an opinion.
  • When human listeners hear a sound and compare it to another sound they have heard, and decide which one they enjoy more, this is a subjective measurement of sound quality.

• Center of Mass of the Human Body

  • Human proportions have been important in art, measurement, and medicine (a well known drawing of the human body is seen in ).
  • In this Atom, we will learn how to measure the COM of a human body.
  • Now, let the subject lie on the beam.
  • Measure the readings (F1, F2) on the scale.
  • where M is mass of the subject.

• Decibels

  • Although the decibel can be used to talk about a number of different subjects, in this atom we are going to cover its use in acoustics and sound level.
  • Loudness is a measure of sound intensity taking frequency into account, and is called a A-weighted decibel, dB(A), or a phon.

• Biological Effects of Radiation

  • The acute effects of radiation were first observed in the use of x-rays when Wilhelm Röntgen intentionally subjected his fingers to x-rays in 1895.
  • Stochastic effects can only be measured through large epidemiological studies in which enough data have been collected to remove confounding factors such as smoking habits and other lifestyle factors.

• Photon Energies of the EM Spectrum

  • Hertz found the waves and was able to infer (by measuring their wavelength and multiplying it by their frequency) that they traveled at the speed of light.
  • In 1895, Wilhelm Röntgen noticed a new type of radiation emitted during an experiment with an evacuated tube subjected to a high voltage.
  • In 1914, Ernest Rutherford (who had named them gamma rays in 1903 when he realized that they were fundamentally different from charged alpha and beta rays) and Edward Andrade measured their wavelengths, and found that gamma rays were similar to X-rays, but with shorter wavelengths and higher frequencies.

• The Simple Pendulum

  • Example:Measuring Acceleration due to Gravity: The Period of a Pendulum.What is the acceleration due to gravity in a region where a simple pendulum having a length 75.000 cm has a period of 1.7357 sStrategy: We are asked to find g given the period T and the length L of a pendulum.
  • When a pendulum is displaced sideways from its resting equilibrium position, it is subject to a restoring force; after it reaches its highest point in its swing, gravity will accelerate it back toward the equilibrium position.
  • If the length of a pendulum is precisely known, it can actually be used to measure the acceleration due to gravity.

• Volume

  • Volume is a measure of the three-dimensional space an object occupies, usually taken in terms of length, width and height.
  • Volume is measured geometrically by multiplying an object's three dimensions—usually taken as length, width and height.
  • Thus a measuring cup can accurately measure the volume of a liquid, whereas a gas will always fill the entire container, more or less uniformly, no matter how little gas there is.
  • A measuring cup can be used to measure volumes of liquids.
  • This cup measures volume in units of cups, fluid ounces and millilitres.

• Measurements: Gauge Pressure and the Barometer

  • Gauge pressure is much more convenient than absolute pressure for practical measurements and is widely used as an established measure of pressure.
  • Barometers are devices used to measure pressure and were initially used to measure atmospheric pressure.
  • Such pressure measuring devices are more practical than hydrostatic barometers for measuring system pressures.
  • Many modern pressure measuring devices are pre-engineered to output gauge pressure measurements.
  • While the aneroid barometer is the underlying mechanism behind many modern pressure measuring devices, pressure can also be measured using more advanced measuring mechanisms.

• Length

  • Length is a physical measurement of distance that is fundamentally measured in the SI unit of a meter.
  • Length can be defined as a measurement of the physical quantity of distance.
  • Many qualitative observations fundamental to physics are commonly described using the measurement of length.
  • In order to describe length in a standardized and quantitative manner, an accepted unit of measurement must be utilized.
  • As such, a standard unit of measurement that is internationally accepted is needed.

• Null Measurements

  • Null measurements balance voltages so there is no current flowing through the measuring devices that would interfere with the measurement.
  • Null measurements balance voltages, so there is no current flowing through the measuring device and the circuit is unaltered.
  • A potentiometer is a null measurement device for measuring potentials (voltages).
  • Many so-called ohmmeters measure resistance.
  • The potentiometer is a null measurement device.