States of Matter and Physical Properties
Understanding matter starts with three key physical properties. Mass is the amount of matter in an object (measured in kg), while volume is the space it occupies (measured in m³). Density connects these two as mass per unit volume , calculated using the formula density = mass ÷ volume.
Objects interact with fluids based on their relative densities. An object with lower density than a fluid will float, while one with higher density will sink. This explains why ships float despite being made of metal – their overall density is less than water.
The three states of matter have distinct particle arrangements. In solids, particles are fixed in position with strong forces between them. Liquids have particles in random motion while maintaining contact. Gases have particles moving freely with significant space between them and weak attractive forces.
Did you know? When calculating the volume of irregular objects, you can use the displacement method - submerging the object in liquid and measuring how much the liquid level rises.
Changes of State and Energy Transfer
State changes occur at specific temperatures. The melting point is when a solid becomes a liquid (same as freezing point in reverse). The boiling point is when a liquid becomes a gas (same as condensation point in reverse). Sublimation is the direct transformation from solid to gas, bypassing the liquid state.
During state changes, something fascinating happens - temperature stops changing! The energy being added or removed is used to break or form bonds between particles. This is called latent heat - energy transferred during state changes without temperature change.
The specific amount of energy needed varies by substance and process. Specific latent heat of fusion is the energy needed to melt 1kg of a solid, while specific latent heat of vaporisation is the energy needed to boil 1kg of liquid into gas. These values are much higher for vaporisation because particles move much further apart.
Gas pressure results from particles colliding with container surfaces. When temperature increases, particles move faster, causing more frequent and forceful collisions, which increases pressure - a principle vital for everything from car tyres to weather systems.