Matter, Density & States
Explore how matter behaves as solids, liquids, and gases; how it changes state with heating and cooling; how latent heat works; how evaporation causes cooling; and how density explains floating and sinking. Use the interactive particle simulator below to compare solids, liquids, and gases β adjust temperature, particle count, and container volume. Use Launch to start, then Play / Pause and Reset to explore.
- States of matter β solids, liquids, and gases in the particle model
- Change of state β melting, boiling, and flat regions on heating curves
- Latent heat β Q = mL during phase change at constant temperature
- Evaporation β surface escape of high-energy molecules and cooling
- Density & buoyancy β Ο = m/V, upthrust, and floating vs sinking
States of Matter
Particle-level view of solids, liquids, and gases.
Key formulas
Real-world applications
Refrigerators & air conditioners
Cooling systems use evaporation and condensation cycles with latent heat to move energy from inside to outside.
Key insight: Latent heat of vaporisation lets refrigerants absorb large amounts of energy at nearly constant temperature.
Floating ships
Huge ships made of dense metal float because their average density (with air-filled hulls) is less than water.
Key insight: Floating depends on overall density and buoyant force, not just on mass.
Hot air balloons
Heating the air inside the balloon lowers its density compared to surrounding cool air, producing an upward buoyant force.
Key insight: Less dense hot air displaces denser cool air, creating upthrust.
Sweating as cooling
Sweat absorbs latent heat from your skin as it evaporates, lowering skin temperature and cooling the body.
Key insight: Evaporation removes high-energy particles and carries away energy as latent heat.
LPG cylinders
Liquefied petroleum gas (LPG) is stored as a liquid under pressure; when released, it vaporises and cools the surroundings.
Key insight: High latent heat and pressure control allow large amounts of gas in small volume.
Common misconceptions & tips
Floating or sinking depends on density, not just weight. A large, heavy ship floats because its overall density (including the air in it) is less than that of water. A small solid metal ball sinks because its density is greater than waterβs.
π Mass alone does not decide floating; average density and displaced fluid (upthrust) matter.
π’ Ο = m / V and upthrust = weight of displaced fluid
π§ͺ In the density simulator, change mass and volume together and compare with fluid density.
Gases are made of particles with mass. A balloon filled with air is heavier than when it is empty. Gas may be low density, but its particles still have mass and can exert pressure and weight.
π Low density is not the same as zero mass; gas particles have mass and contribute to weight.
π’ Ο_gas = m_gas / V (small but not zero)
π§ͺ Think about the mass of a gas cylinder when full vs empty.
At the boiling point, the temperature of a pure liquid remains nearly constant while it boils. Energy supplied goes into breaking intermolecular bonds (latent heat of vaporisation), not into raising the temperature.
π During boiling, added energy changes the state, not the temperature.
π’ Q = mL_v at (nearly) constant T
π§ͺ On the heating-curve simulator, the flat region at boiling shows constant temperature.
Evaporation occurs at all temperatures. At the surface, some high-energy molecules escape into the air even when the bulk liquid is below its boiling point. Boiling is a rapid bulk process; evaporation is slower and surface-based.
π Evaporation is a surface phenomenon that can occur at any temperature.
π’ Rate of evaporation β with temperature, surface area, and wind; β with humidity
π§ͺ In the evaporation simulator, evaporation occurs even below the boiling temperature.
Tip: Use the simulators above to test your intuition about density, phase changes, latent heat, and evaporation.
Chapter Guide
How to Study This Chapter
- Start with states of matter using the particle model
- Build: change of state β latent heat β heating curves
- Connect evaporation to particle energy and cooling
- Apply density and buoyancy to floating and sinking problems
What You'll Learn
- Describe solids, liquids, and gases in terms of particles
- Interpret heating curves and phase changes
- Use Q = mL and Q = mcΞT
- Use density and upthrust to explain floating and sinking
Subtopics β Matter, Density & States
Each subtopic has a dedicated page with explanations and an interactive particle-based simulator.
States of Matter
Matter exists mainly as solid, liquid, or gas. Particle arrangement and motion differ in each state, but particles themselves do not change.
Read more βChange of State
When matter changes state (melting, freezing, boiling, condensation), energy is absorbed or released, often at constant temperature.
Read more βLatent Heat
Latent heat is the energy absorbed or released during a change of state at constant temperature, given by Q = mL.
Read more βEvaporation
Evaporation is the slow escape of high-energy molecules from the surface of a liquid at any temperature below its boiling point.
Read more βDensity
Density Ο is mass per unit volume: Ο = m/V. It helps explain floating and sinking and is central to buoyancy.
Read more β