Japan 中学3年 Science
Chapters: 6
1. Field 1 (5): Motion and energy
Balance, composition and resolution of forces · Laws of motion · Mechanical energy
- 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.
- 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.
- 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.
2. Field 1 (6): Chemical change and ions
Solutions and ions · Chemical change and batteries
- Acids and Bases: Properties, Indicators and Reactions – An acid gives H⁺ ions in water and a base gives OH⁻ ions. Indicators show which one is present by a colour or smell change, and when H⁺ meets OH⁻ they make water, leaving a salt behind.
3. Field 1 (7): Science, technology and humans
Energy and materials · Environmental conservation and use of technology
- 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.
- Environmental Stewardship: Caring for the Planet as We Use Technology – Environmental stewardship means using the Earth's resources carefully so they last, and fixing harm where we can. Every product, from a phone to a hospital machine, has a life cycle: raw materials, making, transport, use and end of life. Each stage uses energy and makes waste. Good stewards keep products longer, choose efficient machines, follow the waste hierarchy (refuse, reduce, reuse, recycle, then dispose), send e-waste to proper recyclers and support laws and company practices that protect nature. Technology can harm the environment, but it can also help: solar panels, LEDs and smart sensors cut waste.
4. Field 2 (5): Continuity of life
Growth and reproduction · Heredity and genes · Diversity and evolution
- Reproduction in Human Beings and Reproductive Health – At puberty, hormones from the brain make the testes and ovaries start working. The male system makes and carries sperm; the female system makes eggs and provides a place (uterus) where a baby develops. Fertilisation happens in the oviduct, and the embryo is fed through the placenta. Reproductive health includes safe choices, contraception, avoiding female foeticide, and preventing sexually transmitted diseases such as HIV/AIDS.
- How Do Organisms Reproduce? DNA Copying and Asexual Reproduction – Reproduction makes new individuals by copying DNA. The copies are never perfect, and these small changes (variations) help a species survive when its surroundings change. In asexual reproduction a single parent makes offspring by fission, fragmentation, regeneration, budding, vegetative propagation or spores.
- Sexual Reproduction in Flowering Plants – Sexual reproduction joins a male and a female gamete, mixing DNA from two parents and creating more variation. In a flower, pollen from the anther reaches the stigma (pollination), grows a pollen tube to the ovule, and the male gamete fuses with the egg (fertilisation). The zygote becomes the embryo, the ovule becomes the seed and the ovary becomes the fruit.
- Heredity and Mendel's Laws – Heredity is the passing of traits from parents to children through genes. Each parent gives one copy of every gene. A dominant copy hides a recessive one, which is why Mendel saw 3:1 in a monohybrid cross and 9:3:3:1 in a dihybrid cross. Genes are pieces of DNA that make proteins, and proteins build the trait.
- Evolution: How New Kinds of Living Things Arise – Variations arise during reproduction. Nature selects those that help survival, so over many generations populations change: this is evolution. Only inherited (DNA) changes pass on; acquired changes do not. Separated populations can become new species. Homologous organs, analogous organs and fossils help us trace who is related to whom, and complex organs evolved step by step.
5. Field 2 (6): Earth and space
Motion of celestial bodies; rotation and revolution · Solar system and stars
- Rotation and Revolution of the Earth – Earth has two main motions. Rotation: it spins on its axis from west to east once in about 24 hours, giving day and night, the daily path of the Sun, local time (15° of longitude per hour) and the bending of winds and currents (Coriolis effect). Revolution: it travels round the Sun on an elliptical orbit once in about 365¼ days. Because the axis is tilted 23.5° from the perpendicular to the orbit plane (the ecliptic) and always points the same way, the overhead Sun moves between the Tropics of Cancer and Capricorn, day length changes, and we get seasons, solstices and equinoxes.
- The Solar System – The Solar System is the Sun and everything its gravity holds: 8 planets, their moons, dwarf planets, asteroids, comets and dust. The inner four planets (Mercury, Venus, Earth, Mars) are small and rocky. After the asteroid belt come the giants: gas giants Jupiter and Saturn, ice giants Uranus and Neptune. Gravity pulls planets towards the Sun while they move sideways, so they travel in orbits; closer planets move faster and have shorter years. It all formed about 4.6 billion years ago from a spinning cloud of gas and dust.
6. Field 2 (7): Nature and humans
Living things and environment · Environmental conservation and use of technology
- Ecosystem, Food Chains and Energy Flow – An ecosystem is all the living things in a place plus the non-living things around them, working together. Energy enters as sunlight, passes one way up a food chain, and only about 10% moves to each next level.
- Environmental Stewardship: Caring for the Planet as We Use Technology – Environmental stewardship means using the Earth's resources carefully so they last, and fixing harm where we can. Every product, from a phone to a hospital machine, has a life cycle: raw materials, making, transport, use and end of life. Each stage uses energy and makes waste. Good stewards keep products longer, choose efficient machines, follow the waste hierarchy (refuse, reduce, reuse, recycle, then dispose), send e-waste to proper recyclers and support laws and company practices that protect nature. Technology can harm the environment, but it can also help: solar panels, LEDs and smart sensors cut waste.