Ukraine 8 клас Physics
Chapters: 2
1. Thermal phenomena
Structure of matter and molecular motion · Temperature and thermal equilibrium · Internal energy and heat transfer · Quantity of heat and specific heat capacity · Thermal expansion · Liquids: surface tension and capillarity · Evaporation, boiling and humidity · Melting and solidification · Fuel combustion and energy conservation · Heat engines
- The Particle Model of Matter – All matter is made of tiny particles that are always moving. In a solid they are close and only vibrate; in a liquid they are close but slide past each other; in a gas they are far apart and move fast in all directions. Heating gives particles more energy: either they move faster (temperature rises) or the forces between them are broken (the state changes while the temperature stays the same). Gas pressure comes from particles hitting the walls.
- Heat Transfer: Conduction, Convection and Radiation – Heat moves in three ways. In conduction, heat passes from particle to particle while the particles stay in place; the rate through a slab is H = kA(T₁ − T₂)/L, where k is thermal conductivity. In convection, the fluid itself moves: hot fluid is lighter and rises, cool fluid sinks. In radiation, heat travels as electromagnetic waves and needs no medium. A blackbody absorbs all radiation and is the best emitter. Its peak wavelength falls as temperature rises (Wien: λmT = b), and its total emitted power grows as T⁴ (Stefan: P = σAT⁴). Newton's law of cooling says a body cools at a rate proportional to its temperature excess over the surroundings.
- Specific Heat Capacity and Heat Balance – Different materials need different amounts of energy to warm up. The specific heat capacity c of a material is the energy needed to raise the temperature of 1 kg of it by 1 °C (or 1 K). Its unit is J/(kg·°C) or J/(kg·K). The energy needed to heat any amount is Q = m × c × ΔT. Water has a very high c (about 4200 J/(kg·°C)), so it heats and cools slowly. When a hot and a cold body touch and nothing is lost, the heat given by the hot body equals the heat taken by the cold body (heat balance). A calorimeter uses this idea to measure c.
- Changes of State: Melting, Boiling, Evaporation and More – A substance can change between solid, liquid and gas when we heat it or cool it. Melting, boiling, evaporation and sublimation need heat. Freezing, condensation and deposition give heat out. While the state is changing, the temperature stays the same, because the heat is used to break (or is released by making) the pull between particles. This hidden heat is called latent heat. Evaporation happens at any temperature, only from the surface, and it cools things down. Changes of state are physical changes: no new substance forms and the mass stays the same.
- Conservation of Energy – Energy cannot be created or destroyed. It only changes from one form to another, or moves from one object to another. The total energy of a closed system stays the same. When there is no friction, mechanical energy (potential + kinetic) stays constant: mgh + ½mv² = constant. With friction, some mechanical energy turns into heat (thermal energy), but the total is still the same. Efficiency = useful energy out ÷ total energy in × 100%.
- Heat Engines – A heat engine is a machine that turns heat into mechanical work. Fuel burns and releases heat Q = q × m, where q is the heat value (heat of combustion) of the fuel and m is its mass. Hot gas expands and pushes a piston or spins a turbine. A four-stroke engine repeats intake, compression, power and exhaust. Only part of the heat becomes useful work; the rest leaves as waste heat. Efficiency η = W ÷ Q × 100%. Engines also release CO₂ and other gases that harm the air and warm the planet.
2. Electrical phenomena
Electric charge and electrification · Interaction of charges and Coulomb's law · Electric current and conductors · Electric circuit: current and voltage · Resistance and Ohm's law · Series and parallel connections · Work and power of current
- Static Electricity – Rubbing two different materials moves electrons from one to the other. The one that gains electrons becomes negative; the one that loses them becomes positive. Charge is never made or destroyed, only moved. Like charges repel and unlike charges attract. A charged object can pull a neutral one by induction. Earthing lets extra charge flow safely away.
- Coulomb's Law: The Force Between Two Charges – Charged objects push or pull each other without touching. Like charges repel and unlike charges attract. For two small (point) charges, the force is F = k·q₁·q₂ / r², where k ≈ 9 × 10⁹ N·m²/C². Double a charge and the force doubles; double the distance and the force falls to one quarter. Charge is never made or destroyed, only moved.
- Ohm's Law – At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V = I × R. R is the resistance, measured in ohms (Ω); 1 Ω = 1 V/1 A. The V–I graph of an ohmic conductor is a straight line through the origin.