Nanometre

A nanometre is a metric unit of measurement, which is equal to one billionth of a meter (1 nm = 10^-9 m).

A nanometre is a unit of measurement of the wavelength of electromagnetic radiation.

Nature

Nature, in the broadest sense, refers to the physical universe including all living and non-living thing.

  • In a limited sense, nature refers to interconnected living organisms including plants, insects, and animals, but excluding non-living phenomena such as oceans, continents, and climate.
  • The concept of nature is a complex and multifaceted one, with varying definitions depending on context and discipline.
  • Although humans are part of nature, human activities such as cities, agriculture, and industries are sometimes seen as separate from other natural phenomena.
  • The study of nature has played a significant role in the histories of both science and art.

Neuron

Neurons are the cells that transmit electrical impulses around the brain and the other parts of the central nervous system.

  • Neurons are the electrically excitable cells that are the fundamental building blocks of the central nervous system of human beings.
  • Neurons interconnect the systems and organs that maintain the body’s essential functions.
  • Neurons send and receive signals that allow us to sense the external world, move, think, form memories and much more.
  • Neurons are of three principal types: motor neurons, sensory neurons and interneurons.
  • Neurons connect together via specialized filaments called synapses.
  • In the neocortex (making up about 80% of the human brain), approximately 70-80% of nervous tissue is in the form of neurons whilst the remainder is composed of interneurons.
About the anatomy of neurons
  • A typical neuron consists of a cell body (soma), dendrites, and a single axon.
  • Dendrites and axons form filament-like extensions of the soma.
  • Dendrites typically form into a profusion of branches as they extend from the soma.
  • An axon can be as long as a metre in length.
  • At the farthest tip of the axon’s branches are axon terminals, where the neuron can transmit a signal across a synapse to another cell.
About interneurons
  • Interneurons are also referred to as relay neurons, connector neurons, intermediate neurons and local circuit neurons each of which helps to explain their function.
  • Interneurons form nodes within neural circuits, enabling communication between sensory or motor neurons and the central nervous system.
  • Interneurons can be further broken down into two groups: local interneurons and relay interneurons.
    • Local interneurons have short axons and form circuits with nearby neurons to analyse small pieces of information.
    • Relay interneurons have long axons and connect circuits of neurons in one region of the brain with those in other regions.
  • The interaction between interneurons allows the brain to perform complex functions such as sense-making.
About neurons and the human retina

Neuron anatomy

About the anatomy of neurons
  • Neurons are the building blocks of the nervous system.
  • A typical neuron consists of a cell body (soma), dendrites, and a single axon.
  • Dendrites and axons form filamentous extensions of the soma.
  • Dendrites typically branch profusely as they extend from the soma.
  • An axon can be as long as a metre in length.
  • At the farthest tip of the axon’s branches are axon terminals, where the neuron can transmit a signal across a synapse to another cell.

Neurons & the human retina

About neurons and the human retina

Newtonian mechanics

Newtonian mechanics is a branch of physics that describes the motion of objects under the influence of forces. It is based on the three laws of motion that were developed by Isaac Newton in the 17th century.

The three laws of motion are:

  1. An object at rest will remain at rest, or if in motion, will remain in motion at a constant speed and in a straight line, unless acted upon by an external force.
  2. The acceleration of an object is directly proportional to the net force acting on it, and inversely proportional to its mass.
  3. For every action, there is an equal and opposite reaction.

These laws can be used to describe a wide range of phenomena, from the motion of planets to the behavior of fluids to the propagation of waves. They are also used in many different fields, including engineering, medicine, and astronomy.

Newtonian mechanics is a very successful theory, and it has been used to predict the motion of objects with a high degree of accuracy. However, it has some limitations. For example, it cannot explain the behavior of light at the atomic and subatomic level. This is because light behaves both like a wave and a particle, which is something that Newtonian mechanics cannot describe.

Despite its limitations, Newtonian mechanics is still a very important and useful theory. It is used in many different fields, and it has helped us to understand the universe in a much deeper way.

Here are some examples of Newtonian mechanics in action:

  • When you throw a ball, the ball accelerates due to the force of gravity.
  • When you ride a bike, you need to pedal to keep moving forward because of the force of friction.
  • When you sit in a chair, the chair exerts an upward force on you that balances the downward force of gravity.
  • When you jump off a cliff, you accelerate due to the force of gravity until you hit the water.

Newtonian mechanics is a fundamental theory of physics, and it is essential for understanding how the world works.

Summary

About sections (temp)

References

Non-spectral colour

A non-spectral colour is a colour that is not present in the visible spectrum and cannot be produced by a single wavelength or narrow band of wavelengths of light.

  • While spectral colours are evoked by a single wavelength of light in the visible spectrum, non-spectral colours are produced by a combination of spectral colours from different parts of the spectrum.
  • Colours evoked by a single wavelength of light are often described as being produced by monochromatic light.
  • Magenta, pink, cyan and brown are examples of non-spectral colours produced by combining different wavelengths of light:
    • Blue and red = magenta
    • Red and purple = pink
    • Blue and green = cyan
    • Red, yellow and blue = brown
  • When we look around us, the colours of things we see rarely include pure spectral colours but are more likely composed of narrow bands of contiguous wavelengths.
  • Since both the RGB and CMY colour models mix primary colours from different parts of the visible spectrum, digital screens and digital printers produce non-spectral colours.
    • The RGB colour model generates a complete range of colours on TVs, computers and phones by blending the primary colours (red, green and blue) in varying proportions.
    • The CMY colour model produces a full spectrum of colours by blending the primary colours of cyan, magenta, and yellow in varying proportions.

Normal

If one line is normal to another, then it is at right angles to it.

In geometry, normal (a or the normal) refers to a line drawn perpendicular to a given line, plane or surface.

  • How a normal appears in a geometric drawing depends on the circumstances:
    • When light strikes a flat surface or plane, or the boundary between two surfaces, the normal is drawn perpendicular to the surface, forming a right angle (90°) with it.
    • Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
    • When light hits a curved surface, the normal line is drawn straight up from the point where the light hits the surface.
    • If light travels directly through the centre of a sphere, the normal line also passes through the centre of the sphere.
Remember that:

Summary

Normal

If one line is normal to another, then it is at right angles. So in geometry, the normal is a line drawn perpendicular to and intersecting another line.

In optics, the normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.

  • Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
  • Light travels in a straight line through a vacuum or a transparent medium such as air, glass, or still water.
  • If light encounters a force, an obstacle or interacts with an object, a variety of optical phenomena may take place including absorption, dispersion, diffraction, polarization, reflection, refraction, scattering or transmission.
  • Optics treats light as a collection of rays that travel in straight lines and calculates the way in which they change direction (deviate) when encountering different optical phenomena.
  • When the normal is drawn on a ray diagram, it provides a reference against which the amount of deviation of the ray can be shown.
  • The normal is always drawn at right angles to a ray of incident light at the point where it arrives at the boundary with a transparent medium.
  • Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.