GA Milestones Science Grade 8 key terms

A testable statement predicting what will happen in an experiment, based on prior observations or knowledge. It must be something you could prove wrong with evidence.

Any factor in an experiment that can change or be changed. Good experiments control most variables so that only the one being tested differs between groups.

The factor the experimenter deliberately changes or manipulates. It is the presumed cause, plotted on the horizontal axis of a graph.

The factor that is measured or observed in response to the independent variable. It is the outcome, plotted on the vertical axis of a graph.

The comparison group in an experiment that does not receive the treatment being tested. It shows what would happen without the change, helping isolate the treatment's effect.

Running the same experimental procedure multiple times to reduce the effect of random error. Consistent results across trials make conclusions more reliable and trustworthy.

The measurements, observations, and facts collected during an investigation. Data may be quantitative, such as numbers, or qualitative, such as descriptions of what was seen.

A judgment about what the results mean, stated only after analyzing the data. It explains whether the hypothesis was supported and what evidence led to that decision.

A visual display of data, such as a bar graph, line graph, or circle graph, chosen to match the type of data. Graphs reveal patterns and trends that tables of numbers can hide.

A well-tested explanation for a broad set of observations, supported by large amounts of evidence from many investigations. Theories are not guesses and can be revised if new evidence demands it.

A statement that describes a consistent pattern in nature, often expressed mathematically, without explaining why the pattern occurs. Laws predict what happens under given conditions.

Information gained through direct observation, measurement, or experiment rather than opinion or logic alone. Scientific claims must be supported by evidence that others can check.

A number paired with a unit that describes a quantity, such as 12 grams or 5 seconds. Accurate measurements require suitable tools and correct reading of scales.

How close repeated measurements are to one another, reflecting consistency of a tool or technique. Precision differs from accuracy, which is closeness to the true value.

A way of writing very large or very small numbers as a number between 1 and 10 multiplied by a power of 10, such as 3.2 x 10^5. It makes extreme values easier to compare and calculate.

The smallest particle of an element that still has the properties of that element. Atoms consist of protons and neutrons in a nucleus, with electrons around it.

A pure substance made of only one kind of atom, which cannot be broken down into simpler substances by chemical means. Each element has a unique atomic number.

Two or more atoms chemically bonded together, forming the smallest unit of a substance that keeps its properties. Molecules may contain atoms of one element or of several elements.

A substance made of atoms of two or more different elements chemically combined in a fixed ratio, such as water or table salt. Compounds have properties unlike their ingredients.

An organized chart of the elements arranged by increasing atomic number, with elements in the same column sharing similar properties. Its rows and columns reveal patterns in reactivity and structure.

A shorthand using element symbols and subscripts to show the kind and number of atoms in a substance, such as H2O or CO2. Subscripts count atoms; coefficients in equations count whole molecules.

A process in which substances break apart and recombine to form new substances with different properties. Signs include color change, gas production, temperature change, and precipitate formation.

A starting substance that is consumed during a chemical reaction, written on the left side of a chemical equation. Reactant atoms are rearranged to build the products.

A new substance formed by a chemical reaction, written on the right side of a chemical equation. Products have properties that differ from those of the reactants.

The principle that matter is neither created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products, so equations must be balanced.

The amount of mass packed into a given volume, calculated as mass divided by volume. Objects less dense than a fluid float in it; denser objects sink.

The amount of matter in an object, measured in grams or kilograms with a balance. Mass stays the same regardless of location, unlike weight.

The amount of space an object or substance occupies, measured in cubic units or liters. It can be found by measuring dimensions or by water displacement.

A characteristic that can be observed or measured without changing the substance's identity, such as color, density, melting point, or conductivity. These help identify and separate materials.

A characteristic describing how a substance behaves when it changes into a different substance, such as flammability or reactivity with acid. Observing it requires a chemical change.

A change of state such as melting, freezing, evaporating, condensing, or sublimating. These are physical changes; the substance's identity stays the same even though particle arrangement changes.

The energy of motion. In any sample of matter, particles are in constant motion, and their average kinetic energy determines the temperature of the sample.

Stored energy that depends on position or arrangement, such as a ball held above the ground or chemical bonds in fuel. It converts to kinetic energy when released.

The principle that energy cannot be created or destroyed, only transferred or transformed from one form to another. The total energy in a closed system stays constant.

Movement of energy from one object or place to another without changing its form, as in heat flowing through a metal spoon. It differs from energy transformation, which changes the form.

Heat transfer through direct contact between particles, as when a metal pan handle warms your hand. It works best in solids, where particles are close together.

Heat transfer by the movement of currents in fluids, where warmer, less dense material rises and cooler, denser material sinks. It drives boiling water, weather, and Earth's mantle motion.

Transfer of energy by electromagnetic waves, which needs no medium and can travel through empty space. Sunlight reaching Earth is the most familiar example.