Everything grade 8 science expects you to be able to say, in 70 short statements. Read it the night before a test, or use it to decide which skill quiz to take next.
Science and Engineering Practices
- Identify the independent, dependent, and controlled variables before running anything.
- A larger sample and repeated trials make a conclusion more trustworthy.
- Correlation is not causation. Two things can rise together for a third reason.
- Claim, evidence, reasoning: state it, back it, then explain why the evidence supports it.
- Every model has limits. Know what yours leaves out before you trust it.
- Engineering iterates: define, design, test, analyze the failure, redesign.
- Optimize by comparing solutions systematically against the same criteria.
Words to know: Observation, Inference, Hypothesis, Prediction, Variable, Independent variable, Dependent variable, Controlled variable, Fair test, Control group, Data, Evidence, Claim, Reasoning
Matter and Its PropertiesMatter and Its Properties
- The number of protons decides which element an atom is.
- The periodic table groups elements so ones with similar properties line up.
- In a chemical reaction, atoms rearrange but are never created or destroyed.
- Balance the count: the same atoms appear on both sides of a reaction.
- Exothermic reactions release thermal energy; endothermic ones absorb it.
- Adding thermal energy during a phase change breaks bonds instead of raising temperature.
- Synthetic materials are made from natural resources through processes people designed.
- Density is mass over volume, and it identifies a substance regardless of sample size.
Words to know: Atom, Element, Compound, Molecule, Proton, Neutron, Electron, Nucleus (atom), Atomic number, Periodic table, Chemical formula, Chemical reaction, Reactant, Product
Forces and MotionForces and Motion
- An object's motion changes only when the net force on it is not zero.
- Acceleration goes up with force and down with mass.
- Forces come in pairs: equal in size, opposite in direction, on different objects.
- Gravitational attraction grows with mass and falls off with distance.
- Electric and magnetic forces act through fields, without contact.
- Charge is conserved. Like charges repel, opposites attract.
- Motion is always described relative to a reference point.
Words to know: Newton's first law, Newton's second law, Newton's third law, Net force, Acceleration, Velocity, Inertia, Field, Electric charge, Static electricity, Electromagnet, Gravitational force, Reference point
EnergyEnergy
- Energy is never created or destroyed, only transferred or transformed.
- Kinetic energy rises with mass and rises much faster with speed.
- Conduction needs contact, convection needs a moving fluid, radiation needs nothing.
- Thermal energy flows from hot to cold until both reach the same temperature.
- Water's high specific heat is why coasts have milder temperature swings.
- Some energy always escapes as waste heat, which is why nothing is 100% efficient.
- Define your system first, then track energy in and out of it.
Words to know: Law of conservation of energy, Work, Power, Conduction, Convection, Radiation, Thermal equilibrium, Specific heat, Chemical energy, Energy efficiency, System and surroundings
Waves and InformationWaves and Information
- Amplitude carries the energy. Frequency and wavelength set pitch and color.
- Wave speed is set mainly by the medium, not by the source.
- Transverse waves move particles across the direction of travel; longitudinal waves move them along it.
- Sound needs a medium. Light does not, and crosses empty space.
- At a boundary a wave can reflect, refract, be absorbed, or be transmitted.
- Digital signals resist noise and copy perfectly, which is why they replaced analog.
Words to know: Frequency, Crest, Trough, Transverse wave, Longitudinal wave, Medium, Electromagnetic spectrum, Transmission, Analog signal, Digital signal, Wave speed
Cells, Structures and Life ProcessesCells, Structures and Life Processes
- All organisms are made of cells, and new cells come only from existing cells.
- The cell membrane controls what enters and leaves; the nucleus holds the instructions.
- Mitochondria release energy from food. Chloroplasts capture light energy.
- Cells build tissues, tissues build organs, organs build systems, systems build the organism.
- Photosynthesis stores energy in glucose; cellular respiration releases it.
- Body systems interact to keep internal conditions steady.
- Sensory receptors detect a stimulus, the brain processes it, then the body responds.
Words to know: Cell, Cell theory, Cell membrane, Cell wall, Nucleus (cell), Mitochondria, Chloroplast, Organelle, Unicellular, Multicellular, Tissue, Organ, Organ system, Cellular respiration
Ecosystems and HeredityEcosystems and Heredity
- Resource availability sets carrying capacity, and carrying capacity limits population size.
- Only about a tenth of the energy at one feeding level reaches the next.
- Matter cycles through an ecosystem; energy flows through and leaves as heat.
- Higher biodiversity generally makes an ecosystem more resilient to disturbance.
- Genes are DNA sections that code for proteins, and proteins produce traits.
- Mutations create the variation that natural selection acts on.
- Sexual reproduction shuffles genes; asexual reproduction copies them.
- Use probability, not certainty, to predict which traits offspring will inherit.
Words to know: Biotic factor, Abiotic factor, Carrying capacity, Limiting factor, Energy pyramid, Symbiosis, Mutualism, Commensalism, Parasitism, Biodiversity, Carbon cycle, Nitrogen cycle, DNA, Gene
Evolution, Fossils and AdaptationEvolution, Fossils and Adaptation
- Natural selection needs variation, inheritance, and differential survival.
- The fossil record shows life and environments changing across geologic time.
- Similar bones in different species point to a shared ancestor.
- Similarities in early embryo development are further evidence of common ancestry.
- Environmental change can push a species to adapt, move, or go extinct.
- Artificial selection is the same mechanism with people doing the choosing.
Words to know: Natural selection, Species, Common ancestor, Fossil record, Homologous structure, Embryological evidence, Artificial selection, Speciation, Genetic variation, Relative dating
Earth and Space SystemsEarth and Space Systems
- Deeper rock layers are older, so the fossil record reads bottom to top.
- Convection in the mantle drives the plates that build mountains and open oceans.
- Rock cycles endlessly among igneous, sedimentary, and metamorphic forms.
- Unequal heating of Earth's surface drives wind, weather, and ocean currents.
- Air masses meeting at a front is what changes the weather.
- Earth's tilt, not its distance from the Sun, causes the seasons.
- Gravity holds the solar system together, and the Sun holds nearly all of its mass.
- Space distances are so vast we measure them in light-years.
Words to know: Geologic time scale, Rock cycle, Igneous rock, Sedimentary rock, Metamorphic rock, Plate tectonics, Convergent boundary, Divergent boundary, Transform boundary, Convection current, Seismic wave, Air mass, Front, Humidity
Earth, Human Activity and EngineeringEarth, Human Activity and Engineering
- Resources are concentrated where past geologic processes put them, not where people live.
- Total human impact rises with both population size and per-person consumption.
- Hazards cannot be prevented, but forecasting and design reduce the damage.
- Greenhouse gases trap thermal energy, and their rise tracks the rise in global temperature.
- Monitoring gives the data needed to test whether a solution is working.
- Every engineering solution trades one benefit against another cost.
Words to know: Uneven resource distribution, Fossil fuel, Greenhouse gas, Climate change, Global temperature rise, Per capita consumption, Forecasting, Mitigation, Sustainability, Cost-benefit analysis