Particle Model and Energy

Ever wondered why ice floats or how a kettle works? The particle model explains it all! This model shows how particles behave differently in solids, liquids and gases.

In solids, particles vibrate in fixed positions with a regular structure. Liquids have particles that slide over each other while remaining tightly packed. Gas particles move randomly and are spread far apart. This arrangement affects density - solids are usually most dense, gases least dense.

Density measures how much mass is packed into a given volume: Density = mass (kg) ÷ volume (m³). You can measure mass using a balance and volume either by calculating dimensions (for regular objects) or using water displacement (for irregular objects).

Remember: The internal energy of a substance is the total kinetic and potential energy of all its particles. Temperature specifically measures the average kinetic energy of these particles.

When materials change state, they require energy without changing temperature. This is called specific latent heat - the energy needed to change 1kg of a substance from one state to another at constant temperature $E = mL$. The specific heat capacity tells us how much energy is needed to raise 1kg of a material by 1°C $E = mcΔθ$. Water has a high value $4,200 J/kg°C$, meaning it heats up and cools down slowly.

Gas particles create pressure by colliding with container walls. More particles or faster movement means higher pressure. At constant volume, pressure increases directly with temperature as particles gain energy and collide more frequently.

Required Practicals and Gas Pressure

Measuring density is something you'll likely do in your exams, so make sure you know how! For regular objects, measure the mass and calculate volume using length × width × height. For irregular objects like stones, use water displacement - the volume of water pushed out equals the object's volume.

For liquids, it's even simpler. Measure the mass of an empty container, add a known volume of liquid, measure again, and calculate the difference in mass. Then divide this mass by the volume to find density.

The specific heat capacity practical measures how much energy is needed to heat a material. You'll need to:

1. Set up an insulated metal block with an immersion heater and thermometer
2. Record the starting temperature
3. Supply energy for a set time $E = Pt$
4. Record the highest temperature reached

Practical tip: In the specific heat capacity experiment, some energy always escapes to the surroundings, which causes an overestimate of the material's specific heat capacity.

For those studying single Physics, understanding gas pressure is essential. Boyle's Law states that pressure is inversely proportional to volume (at constant temperature): P₁V₁ = P₂V₂. This means if you halve a gas's volume, you double its pressure.

Temperature affects pressure too - when a gas heats up in a fixed container, the particles move faster and collide more often with the walls, increasing pressure. When you compress a gas (like in a bike pump), you're doing work that transfers energy to the gas, increasing its internal energy and temperature.