Germany Jahrgangsstufe 9 Physics
Chapters: 4
1. Energy as a conserved quantity
Mechanical energy, work and power · Electrical energy and power
- 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.
- Electric Power and Electrical Energy – Electric power is the rate of using electrical energy: P = VI = I²R = V²/R, in watts. Energy used = power × time. At home energy is measured in kilowatt-hours: 1 kWh = 1 unit = 3.6 × 10⁶ J. Bill = units × rate.
2. Atoms
Photons, spectra and atomic energy levels
- Structure of the Atom – An atom has a tiny, heavy, positive nucleus made of protons and neutrons. Electrons move around it in fixed shells K, L, M, N. The number of protons (Z) tells the element; protons + neutrons give the mass number (A). Outer electrons decide valency. Isotopes share Z; isobars share A.
3. Heat and thermodynamics
Particle model of heat and gases · Heat transfer and the greenhouse effect
- 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.
4. Profile area (science-technology school)
Physics of climate change · Applied energy topics and pressure
- Climate Change and the Greenhouse Effect – Climate is the average weather of a place over about 30 years. Greenhouse gases like carbon dioxide and methane trap some of the heat the Earth gives off. Humans have added a lot more of these gases by burning fossil fuels and cutting forests, so the Earth is warming. This causes melting ice, rising seas and more extreme weather. We can cut emissions (mitigation) and prepare for changes (adaptation).
- Minerals and Energy Resources – Minerals are natural substances found in rocks. They are metallic (ferrous or non-ferrous), non-metallic, or energy minerals. Energy comes from conventional sources like coal, petroleum, natural gas and electricity, and from non-conventional sources like sun, wind, nuclear, biogas, tides and heat from the Earth. Both minerals and energy must be conserved.