Evolving Models of Gas Behaviour (AQA A Level Physics)

• Our knowledge and understanding of the behaviour of gases has changed significantly over time
• The gas laws were developed by many scientists over thousands of years

Democritus (2000 years ago)

• Ancient Greek and Roman philosophers, such as Democritus, had some ideas about gases, some of which are quite close to what we now know to be true
• Democritus thought that if you cut an object in half, and each half has the same properties as the original object, that you can continue to cut the object into smaller and smaller pieces until it can no longer be divided
• He named the infinitesimally small pieces of matter atomos meaning 'indivisible'
  • This is the etymology of the word 'atom'

• Both of the two most well-known Greek philosophers, Aristotle and Plato, rejected his theories
  • Due to their influence, Democritus's theories were not accepted until almost 2000 years later

Robert Boyle (1662)

• Robert Boyle discovered the relationship between pressure and volume at a constant temperature
• This came to be known as Boyle's Law

Guillaume Amontons (1699)

• Amontons, and later also by Joseph Louis Gay-Lussac (1809), discovered the relationship between the temperature and the pressure of a gas at constant volume
• This came to be known as the Pressure Law

Jacques Charles (1787)

• This was then followed by Charles who discovered the relationship between the volume of a gas and its temperature at constant pressure
• This came to be known as Charles's Law

Daniel Bernoulli (18th Century)

• Bernoulli assumed that gases were made up of tiny particles which sparked the beginning of kinetic theory
  • However, kinetic theory wasn't widely accepted for at least another couple of hundred years

• Bernoulli is also known for the Bernoulli's Principle of fluid dynamics, which is a statement of the conservation of energy appropriate for flowing fluids

Robert Brown (1827)

• Brown was an English botanist who discovered Brownian Motion, the random motion of particles in a fluid, which helped support kinetic theory
• This is because Brownian Motion gave evidence that air is made up of tiny atoms or molecules that move very quickly and randomly

Albert Einstein (1905)

• In Einstein's miracle year of 1905, he produced a paper on how kinetic theory was used to make predictions for Brownian motion
  • Only then did the atomic and kinetic theory of particles start to become more widely accepted

• His publication of Brownian Motion became one of his most cited papers of all time, due to its far-reaching implications in both chemistry and physics

• Scientific ideas are rarely accepted immediately and require a rigorous process validation process
• Other scientists must repeat experiments and obtain the same conclusions for a theory to be accepted
• The theory that gases are made up of randomly, fast-moving particles may seem obvious now, but the existence and nature of particles was ground-breaking in all the scientists and took many centuries to completely understand