NGSA Science cheat sheet

Newton's second law: net force equals mass times acceleration (F = ma); acceleration is in the direction of the net force and is zero when forces balance.

Kinetic energy = ½mv²; gravitational potential energy near Earth's surface = mgh. Mechanical energy is conserved only when nonconservative forces such as friction do negligible work.

Waves: speed = frequency × wavelength (v = fλ). For a fixed medium speed, increasing frequency decreases wavelength; amplitude controls energy/intensity, not speed.

Light behavior decision rule: reflection = bounce off a surface; refraction = bending due to speed change between media; diffraction = spreading around obstacles or through slits.

Electric circuits: Ohm's law V = IR. In series, current is the same through all components and resistances add; in parallel, voltage is the same across branches and currents add.

Conservation laws: mass, energy, and charge are conserved in closed systems. In chemical reactions, atoms are rearranged but never created or destroyed, so equations must balance.

Density = mass / volume. An object floats in a fluid when its average density is less than the fluid's density; it sinks when greater.

Acids release H⁺ (protons) in water and have pH below 7; bases accept H⁺ (or release OH⁻) and have pH above 7. Neutralization produces water and a salt.

Phase changes: melting, boiling, and sublimation absorb energy; freezing, condensation, and deposition release energy. Temperature stays constant during a phase change at a given pressure.

Cell theory: all living things are made of cells, the cell is the basic unit of life, and new cells arise from existing cells.

Prokaryotic vs. eukaryotic decision rule: prokaryotes lack a membrane-bound nucleus and organelles; eukaryotes have a nucleus and membrane-bound organelles.

Photosynthesis converts light energy, CO₂, and H₂O into glucose and O₂ in chloroplasts; cellular respiration converts glucose and O₂ into CO₂, H₂O, and ATP in mitochondria.

DNA structure: double helix with base pairing A–T and C–G. During replication the strands separate and each serves as a template (semiconservative).

Protein synthesis flow: DNA is transcribed to mRNA in the nucleus, then translated by ribosomes using codons matched to tRNA anticodons.

Natural selection requires heritable variation, differential reproductive success, and environmental pressure; it acts on individuals but changes populations over generations.

Homeostasis is maintained by negative feedback: a deviation triggers a response that reduces the deviation. Positive feedback amplifies change, as in childbirth contractions.

Energy flows one way through ecosystems (producers → consumers → decomposers) while matter cycles through biogeochemical pathways such as the carbon and nitrogen cycles.

Genotype vs. phenotype: genotype is the allele combination; phenotype is the observable trait. Dominant alleles mask recessive alleles in heterozygotes (Aa).

Earth's structure (outer to inner): crust, mantle, outer core, inner core. The outer core is liquid and its motion generates Earth's magnetic field.

Plate tectonics: divergent boundaries create new crust (mid-ocean ridges), convergent boundaries cause subduction or mountain building, and transform boundaries cause lateral faulting and earthquakes.

Rock cycle: igneous forms from cooling magma/lava, sedimentary from compaction and cementation of sediments, metamorphic from heat and pressure on existing rock.

The rock record: superposition means older layers lie below younger ones; index fossils and radioactive dating establish relative and absolute ages.

Water cycle processes: evaporation, transpiration, condensation, precipitation, infiltration, runoff. Energy from the Sun drives the cycle.

Earth's tilt of about 23.5° causes seasons; the hemisphere tilted toward the Sun receives more direct sunlight and longer days.

Moon phases result from the changing angle between Earth, the Moon, and the Sun; a solar eclipse occurs at new moon, a lunar eclipse at full moon.

Solar system order from the Sun: Mercury, Venus, Earth, Mars (rocky), then Jupiter, Saturn, Uranus, Neptune (gas/ice giants). Gravity governs orbital motion.

Stars: apparent brightness depends on luminosity and distance. The Hertzsprung–Russell diagram plots luminosity against temperature, showing main sequence, giants, and white dwarfs.

Engineering design cycle: define the problem, research constraints, generate solutions, select and prototype, test and evaluate, then iterate. Constraints include budget, materials, time, and safety.

Criteria vs. constraints: criteria are goals the solution must achieve; constraints are limits it must work within. Trade-offs occur when improving one criterion worsens another.

Optimization: the best design is not always the maximum of one variable; performance is evaluated against multiple criteria and constraints simultaneously.

Models and prototypes are simplified representations used to test ideas; their validity depends on how well they reflect the relevant features of the real system.

Risk and benefit analysis: technologies have intended benefits and possible side effects; decisions weigh evidence, cost, and unintended consequences.

Systems thinking: a system has components, inputs, processes, outputs, and feedback. Feedback loops can stabilize or destabilize a system.

Scale and measurement: unit conversions and significant figures matter. A measurement is reported with an uncertainty, and precision differs from accuracy.

Technology impacts: new technologies can change society and environment; evaluating them requires considering energy use, materials, and life-cycle effects.

Crosscutting concept - patterns: observed regularities can be used to classify, predict, and explain phenomena across disciplines.

Crosscutting concept - cause and effect: mechanisms explain why events occur; correlation alone does not establish causation.

Crosscutting concept - scale, proportion, and quantity: phenomena occur at scales from atomic to cosmic, and relative size affects which factors dominate.

Crosscutting concept - systems and system models: boundaries, inputs, outputs, and interactions define a system; models approximate but simplify it.

Crosscutting concept - energy and matter: energy flows and matter cycles; tracking them reveals what drives a process.

Crosscutting concept - structure and function: the shape and arrangement of parts determine what a system or object can do.

Crosscutting concept - stability and change: systems can remain stable through feedback or change due to forces; rates of change can be quantified.

Scientific practices: ask questions, plan and carry out investigations, analyze data, construct explanations, and argue from evidence.

Experimental design: a controlled experiment changes one independent variable while holding others constant; the dependent variable is what is measured, and a control group provides a baseline.