A gas enters a tank through a valve that is being manipulated in a particular way - Leaving Cert Chemistry - Question 3 - 2016

The relationship between pressure and volume is described by Boyle's Law, which states that the pressure of a given amount of gas is inversely proportional to its volume when temperature is held constant. This can be expressed mathematically as:

$P \times V = k$

where $k$ is a constant. For example, if the volume of a gas is halved, the pressure will double, assuming the temperature remains constant.

'Fluid' is a broad term that encompasses both liquids and gases. Fluids are substances that can flow and do not have a fixed shape, meaning they take the shape of their container. In a fluid, the particles are free to move past one another, allowing the substance to adapt to the shape of the environment.

The behavior of a fluid as a liquid or a gas is influenced by several factors:

1. Compressibility: Gases are highly compressible due to the large spaces between particles, while liquids are virtually incompressible.
2. Viscosity: Liquids generally have higher viscosity than gases, resulting in greater resistance to flow.
3. Density: Gases have lower density compared to liquids, which affects buoyancy and flow behavior.
4. Temperature and Pressure: Changes in temperature and pressure can significantly affect the state of the fluid, causing transitions between liquid and gas phases (e.g., boiling, condensation).