Density and Particle Theory

Density is simply how much mass is packed into a given space - it's mass divided by volume $ρ = m/V$. Think of it like comparing a sponge to a brick of the same size - the brick has much higher density because it contains more mass in the same volume.

The golden rule is simple: higher density objects sink, lower density objects float. This explains why oil floats on water and why helium balloons rise up to the ceiling.

For your practicals, measuring density depends on the object's shape. Irregular objects go straight into a measuring cylinder with water - the volume displaced equals the object's volume. Regular objects use a eureka can where you collect and measure the overflow water.

Gas pressure happens because particles constantly smash into container walls. Heat up a gas and those particles move faster with more energy, creating higher pressure - which is exactly why that balloon might pop in hot weather!

Quick Tip: Remember the density triangle - cover what you want to find, and the formula appears!

States of Matter and Energy Changes

The three states of matter behave completely differently because of how their particles are arranged and move. Solids have particles locked in fixed positions that just vibrate, liquids let particles slide past each other, and gases have particles zooming around freely with loads of space between them.

Internal energy is the total kinetic and potential energy of all particles in a substance. When you heat something, you're pumping energy into those particles - but here's the clever bit: during melting or boiling, temperature stays constant even though you're still adding heat.

This happens because the energy goes into breaking the forces holding particles together (increasing potential energy) rather than making them move faster (increasing kinetic energy). It's like using energy to break chains rather than making the prisoners run faster!

Specific heat capacity tells you how much energy you need to warm up 1kg of something by 1°C, whilst specific latent heat tells you the energy needed to completely change the state of 1kg of material.

Remember: During state changes, temperature stays constant - all that energy goes into breaking particle bonds!

Essential Formulas

These two formulas are your best mates for energy calculations, and they're easier than they look!

For latent heat: E = mL. This calculates the energy needed to change state - like melting ice or boiling water. Just multiply the mass by the specific latent heat value (which you'll usually be given in exams).

For specific heat capacity: ΔE = mcΔθ. This works out energy changes when temperature actually changes. The Δ symbols just mean "change in" - so it's change in energy equals mass × specific heat capacity × change in temperature.

The key difference? Use latent heat when stuff is melting, boiling, or freezing (temperature stays the same). Use specific heat capacity when things are warming up or cooling down (temperature actually changes).

These formulas pop up constantly in physics exams, so practise rearranging them to find different variables. Cover up what you want to find, and the rest shows you the calculation!

Exam Tip: Always check your units match the formula - convert grams to kilograms if needed!