France Première Scientific Education
Chapters: 5
1. A long history of matter
Chemical elements and radioactivity · Ordered structures: crystals · A complex structure: the living cell
- Radioactivity: Alpha, Beta, Gamma and Half-Life – Some atomic nuclei are unstable. They give out radiation at random to become more stable. This is radioactive decay. Alpha (2 protons + 2 neutrons), beta (a fast electron) and gamma (a wave of energy) are the three main kinds. Half-life is the time for half of the unstable nuclei to decay.
- The Solid State – In a solid the particles sit close together and only vibrate in place, so a solid keeps its shape. In crystalline solids the particles repeat in a regular pattern; in amorphous solids (like glass) they do not. The smallest repeating box is the unit cell. Simple cubic holds 1 particle, body-centred cubic 2 and face-centred cubic 4. By the bonds holding them, crystals are ionic, covalent network, molecular or metallic.
- The Cell: Basic Unit of Life – Every living thing is made of cells. Robert Hooke first saw cells in cork in 1665. Cells are prokaryotic (no true nucleus, like bacteria) or eukaryotic (true nucleus). Plant cells have a cell wall, chloroplasts and a big vacuole; animal cells do not. Each organelle has a job. Water enters and leaves cells by osmosis. Cells make new cells by mitosis (growth) and meiosis (sex cells).
2. The Sun, our energy source
Solar radiation · Earth’s radiation balance · Photosynthesis · Heat balance of the human body
- Solar Energy: From the Sun to Your Plug – The Sun makes energy by nuclear fusion: hydrogen nuclei join to make helium, and a little mass becomes a lot of energy (E = mc²). The hot surface (about 5800 K) radiates mostly visible light (Wien's law), and its total power grows as T⁴ (Stefan's law). About 1361 W reaches each square metre facing the Sun at the top of the atmosphere; about 1000 W/m² reaches the ground on a clear day. Sunlight hitting at a slant spreads over more area, which explains latitude and seasons. Solar cells turn light into electricity: P = intensity × area × efficiency × cos(angle). Solar water heaters turn light into heat.
- The Greenhouse Effect – The Sun heats Earth with visible light. About 30% is reflected straight back to space (albedo ≈ 0.30). The rest warms the ground, which gives off infrared radiation. Greenhouse gases – water vapour, carbon dioxide, methane, nitrous oxide – let visible light through but absorb infrared and send part of it back down. Earth settles at the temperature where energy in equals energy out. Without greenhouse gases Earth would average about −18 °C; with them it is about +15 °C. Adding more CO₂ and CH₄ (from burning fuels, farming, landfills) strengthens the effect and warms the planet.
- Life Processes and Photosynthesis – Life processes are the jobs every living body must keep doing to stay alive: nutrition, respiration, transport and excretion. Green plants do nutrition by photosynthesis: using sunlight and chlorophyll, they turn carbon dioxide and water into glucose and give out oxygen.
- Homeostasis – Homeostasis is how the body keeps its internal environment (blood and tissue fluid) steady even when the outside world changes. It controls body temperature (about 37 °C), blood glucose (about 4–6 mmol/L), water and salt, and blood pH (about 7.4). It mostly uses negative feedback: a receptor senses a change, a control centre decides, and an effector brings the level back to its set point.
3. Earth, a singular planet
The shape of the Earth · Dating the Earth · Earth in the Universe
- The Shape and Size of the Earth – The Earth is a slightly flattened sphere about 6,371 km in radius. Eratosthenes found its size by comparing the Sun's shadow angle in two towns: circumference = distance between towns x 360 / angle. Surveyors use triangulation, and latitude and longitude help us find distances on a sphere (1 degree of latitude is about 111 km).
- 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.
4. Sound and music
Sound as vibration · Music and numbers (scales) · Digitising sound · Hearing music
- Sound – Sound is made by vibrating objects. It travels through a medium (air, water, solids) as a longitudinal wave: particles move back and forth, making crowded parts (compressions) and spread-out parts (rarefactions). Frequency (Hz) sets the pitch, amplitude sets the loudness, and speed v = f × λ. Sound cannot travel in vacuum. Humans hear 20 Hz to 20,000 Hz; below is infrasound, above is ultrasound. Reflected sound gives echoes, used and controlled in buildings.
- Mathematics in Music – A sound is a wave. Its frequency f (in hertz) is the pitch, and its period is T = 1 / f. Strings of length ratio 1 : 2 sound an octave apart, 2 : 3 a fifth. A piano octave has 12 equal steps, each a factor of 2^(1/12) = 1.0595. Rhythm splits a bar into fractions, for example 3 + 3 + 2 = 8 beats.
- Data Representation: How Computers Store Numbers, Text, Images and Sound – Data is raw facts; information is data given meaning; knowledge is information we can use. A computer stores all data as bits (0 or 1). 8 bits make a byte, and 1 kB = 1000 bytes, 1 MB = 1000 kB, 1 GB = 1000 MB, 1 TB = 1000 GB. Numbers are stored in binary, where place values double: 1, 2, 4, 8 and so on. Text uses a character set: in ASCII 'A' is 65; Unicode covers every script. A bitmap image is a grid of pixels; size = width × height × colour depth. Sound is sampled: size = sample rate × bit depth × seconds. Vector images store shapes instead of pixels. Compression makes files smaller: lossless keeps every bit, lossy throws some detail away.
- Physics of the Ear – The ear turns tiny pressure waves into nerve signals. The eardrum vibrates, three small bones (ossicles) act as a lever, and because the eardrum is much bigger than the oval window the pressure rises about 20 times. In the cochlea the basilar membrane vibrates at a place that depends on frequency: high frequencies near the base, low near the apex. Hair cells there send signals to the brain. A healthy young ear hears about 20 Hz to 20 kHz and is most sensitive at 2–5 kHz. The threshold of hearing at 1 kHz is I₀ = 1.0 × 10⁻¹² W m⁻². Intensity level is L = 10 log₁₀(I/I₀) dB. Hearing gets worse with age (mostly high frequencies) and with loud noise (a dip near 4 kHz).
5. Experimental and digital project
Measurement and data project
- The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.