An object is a physical entity and so a thing that has mass and occupies space.

  • Objects can be described based on their properties such as size, shape, texture, and colour.
  • The perception of an object is a result of the brain’s interpretation of sensory information received from the physical entity.
  • All objects are composed of atoms or molecules, which are the building blocks of matter.
  • The properties of the atoms and molecules that make up an object determine its physical and chemical properties.
Is a rainbow an object?
About the colour of objects
  • Objects are composed of atoms, which bond together to form molecules, elements, and compounds. These different combinations of atoms give objects their unique properties and determine how they react to light.
  • Objects appear to have different colours because they absorb some wavelengths of light and reflect or transmit others. The wavelengths that are reflected determine the colour of an object seen by an observer.
  • In physics, the absorption and reflection of light are explained as follows:
      • Atoms are composed of protons, neutrons and electrons. Protons and neutrons form the nucleus and electrons orbit the nucleus.
      • The orbit, or energy level, of an electron in an atom can change when the electron gains or loses energy.
      • When an electron absorbs a photon of light, it gains energy and moves to a higher energy level so a higher orbit.
      • The difference between the initial and final energy levels of the electron is equal to the energy of the absorbed photon.
      • When an electron moves to a higher energy level it is in an unstable state and eventually returns to its original lower energy level.
      • When the electron returns to its original lower energy level, it emits a photon of light with a frequency and wavelength corresponding to the energy difference between the two levels.
      • The difference between any two energy levels of an electron is specific to the type of atom and can be thought of as being equal to a “quantum” of energy,  where a quantum is understood to mean an indivisible unit of energy.
      • Every type of atom has a unique set of energy levels, and so it emits or absorbs photons of light at specific wavelengths or colours.
    • The colour of objects perceived by an observer can be affected by the lighting conditions in which they are viewed and so by the spectral power distribution of the light source.
    • The surface texture of objects affects how light interacts with them. Smooth and polished surfaces reflect light in a regular pattern, while rough and textured surfaces scatter light and colour in many directions.
    • Transparent objects allow much of the light that strikes them to pass through. The colour seen by an observer is affected by impurities or defects in the material and by the colour of the background against which they are viewed.
    • In the case of opaque objects, the surface of the object reflects, absorbs or scatters light, which determines what is seen by the observer.

An object is a material thing that can be seen and touched.

  • An object is intuitively assumed to exist and to be responsible for a unified experience, consisting of visual and other sensations and perceptions.
  • Every object, material, medium or substance that we can see is made of matter of one kind or another. The key differentiating factor is the elements and molecules they are constructed from.
  • You will have come across the elements that make up the periodic table.
  • A close look at molecules reveals that they are made up of atoms composed of electrons surrounding a nucleus of protons and electrons.
  • Light illuminates objects. In a nutshell, different elements and molecules react to light in different ways because of their atomic structure and the particular way they combine to form mixtures or compounds.
  • In the case of an opaque object, it is the molecules that form its surface that determine what happens when light strikes it. Translucent and transparent objects behave differently because light can travel through them.
  • Another factor that needs to be taken into account when light strikes an object is surface finish. A smooth and polished surface behaves differently from one that is rough, textured or covered in ripples.