Poland Szkoła podstawowa, klasa VII Physics
Chapters: 5
1. Cross-cutting skills
Working with information and phenomena · Measurement and experiments
- Data Analysis – Data analysis means turning raw data into answers. It follows a cycle: ask a question, collect data, clean it (remove errors, repeats and blanks), organise and transform it, analyse it with summaries such as mean, median, range and patterns, show it with a good chart, and draw a careful conclusion. Watch for outliers, small samples and bias, and remember that a correlation between two things does not prove that one causes the other. Data must also be stored safely and used with permission.
2. Motion and forces
Describing motion and speed · Accelerated motion · Forces and Newton's laws · Gravity and free fall · Experiments: motion and forces
- Motion: Distance, Speed, Velocity, Acceleration and Graphs – An object is in motion when its position changes with time. Distance is the full path length (a scalar); displacement is the straight gap from start to finish with a direction (a vector). Speed = distance ÷ time; velocity = displacement ÷ time. Acceleration = change in velocity ÷ time. The slope of an s–t graph gives velocity, the slope of a v–t graph gives acceleration, and the area under a v–t graph gives the distance. For uniform acceleration: v = u + at, s = ut + ½at², v² = u² + 2as.
- Force and Laws of Motion – A force is a push or a pull. Balanced forces (net force zero) do not change motion; an unbalanced force changes speed or direction. Friction opposes sliding. First law: a body keeps its state of rest or uniform motion unless an unbalanced force acts (inertia; heavier bodies have more inertia). Momentum p = mv. Second law: F = ma (rate of change of momentum), 1 N = 1 kg m/s². Third law: forces come in equal and opposite pairs acting on two different bodies. For a system with no outside force, internal forces cancel and total momentum is conserved.
- Free Fall – A body is in free fall when gravity is the only force acting on it. Near the Earth every freely falling body speeds up by about 9.8 m/s every second, whatever its mass. This is the acceleration due to gravity, g ≈ 9.8 m/s². For a body dropped from rest: v = g t and h = ½ g t². Air resistance makes light, wide things like feathers fall slower. Weight is the pull of gravity: W = m × g.
3. Energy
Work and power · Forms of mechanical energy and conservation
- Work, Energy and Power – Work is done when a force moves an object: W = F × s, measured in joules (J). Energy is the ability to do work. A moving body has kinetic energy ½mv²; a raised body has potential energy mgh. Energy is never made or destroyed, only changed from one form to another. Power is how fast work is done: P = W ÷ t, in watts. Simple machines like levers and pulleys let a small effort move a big load.
4. Thermal phenomena
Temperature and internal energy · Heat transfer · Changes of state · Experiments: thermal phenomena
- Temperature – Temperature tells us how hot or cold something is. Inside every object, tiny particles are always moving; temperature measures their average kinetic energy (how fast they jiggle on average). We measure it with a thermometer, in degrees Celsius (°C), kelvin (K, the SI unit) or degrees Fahrenheit (°F). K = °C + 273 and °F = 9/5 × °C + 32. The lowest possible temperature is absolute zero, 0 K = −273 °C. When a hot and a cold object touch, heat flows from hot to cold until both have the same temperature (thermal equilibrium).
- 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.
- 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.
5. Properties of matter
Mass and density · Pressure in fluids · Buoyancy and molecular forces · Experiments: properties of matter
- Density – Density tells how much mass is packed into each unit of volume: ρ = m ÷ V. Its SI unit is kg/m³; in the lab we often use g/cm³ (1 g/cm³ = 1000 kg/m³). Water has density 1 g/cm³. An object less dense than a liquid floats in it; a denser one sinks.
- Pressure in Fluids and Pascal's Law – A fluid (liquid or gas) pushes on every surface it touches. Pressure is this normal force per area, P = F/A. Because of gravity, the fluid above a point has weight, so pressure grows with depth: P = P₀ + ρgh. Points at the same depth in a still liquid have the same pressure, whatever the vessel's shape. Pascal's law says an extra pressure applied to an enclosed fluid reaches every point equally. The hydraulic lift and brakes use this: a small force on a small piston becomes a big force on a big piston, F = f × A/a.
- Archimedes' Principle: Why Things Float or Sink – Any object in a liquid (or gas) is pushed up by a force called upthrust or buoyant force. Archimedes' principle says this upthrust equals the weight of the liquid the object pushes aside: F = ρ g V. An object floats if its density is less than the liquid's, sinks if it is more. A floating object sinks just deep enough that upthrust equals its weight.