Energy and Electricity Fundamentals

Energy is never created or destroyed - it just moves from one form to another, which is brilliant news because it makes physics predictable! You'll encounter different energy stores like gravitational potential energy (mgh), kinetic energy (½mv²), and elastic potential energy (½ke²). When something falls, gravitational potential energy converts to kinetic energy - simple as that.

Electrical circuits work in two main ways: series and parallel. In series circuits, current stays the same throughout $I₁ = I₂ = I₃$, but voltage adds up. In parallel circuits, it's the opposite - voltage stays constant whilst current splits up. This is why Christmas lights used to go out completely when one bulb failed (series), but modern ones keep working (parallel).

Power measures how quickly energy transfers $P = E/t$, and efficiency tells you how much useful energy you actually get out compared to what you put in. Real-world devices always waste some energy, usually as heat - that's why your laptop gets warm when you're gaming.

Quick Tip: Remember that Ohm's Law $V = IR$ only works for resistors at constant temperature - filament bulbs get hot and their resistance changes!

States of Matter and Forces

Matter exists in three main states - solid, liquid, and gas - with particles that have different amounts of kinetic energy and different forces between them. Heating a system gives particles more kinetic energy, making them move faster until they have enough energy to break bonds and change state.

Density calculations $ρ = m/V$ help you work out whether objects will float or sink. For gases, there's a really useful relationship: pressure and volume are inversely proportional when temperature stays constant (PV = constant). This explains why a balloon shrinks in the fridge.

Forces come in two types: contact forces (like friction and air resistance) and non-contact forces (gravity, magnetism, electrostatics). Weight is different from mass - mass is how much stuff you have, whilst weight depends on gravitational field strength. On the Moon, your mass stays the same but your weight becomes much less.

Moments and equilibrium are about turning effects. A moment equals force × distance from the pivot $M = Fd$. Levers work by increasing the distance from the pivot where you apply force, so you need less effort to get the same turning effect.

Real-World Connection: Understanding pressure $P = F/A$ explains why drawing pins have sharp points and why you sink into sand but not concrete!