Praxis Physical Science 5485 key terms

A testable, tentative explanation for an observed phenomenon that predicts a specific outcome and can be supported or rejected by evidence gathered through experiment or observation.

The factor a researcher deliberately changes or manipulates in an experiment so its effect on another measured factor can be observed; also called the manipulated variable.

The factor that is measured or observed in an experiment; its value is expected to respond to changes in the independent variable and is sometimes called the responding variable.

An investigation in which all variables except the independent variable are held constant, allowing a fair comparison that isolates the effect being tested.

A well-substantiated explanation of some aspect of the natural world that is based on a body of evidence, has survived repeated testing, and can still be revised as new evidence appears.

How close a measured value is to the true or accepted value; a measurement can be accurate only if it is free of large systematic errors.

How closely repeated measurements of the same quantity agree with one another; precise measurements may still be inaccurate if a systematic error shifts them all in the same direction.

The digits in a measurement that carry meaningful information about its precision, including all certain digits plus one estimated digit; they guide how calculated results should be rounded.

A systematic cycle used to solve practical problems: defining a need, researching, generating and evaluating solutions, building a prototype, testing, and refining the design based on results and constraints.

The tendency of an object to resist changes in its state of motion; an object at rest stays at rest, and a moving object keeps moving at constant velocity, unless a net external force acts.

The net force on an object equals its mass times its acceleration (F = ma); a larger net force produces greater acceleration, while a larger mass produces less acceleration for the same force.

A measure of an object's motion equal to its mass multiplied by its velocity; momentum is a vector quantity, so direction matters when objects collide or interact.

In a closed system with no net external force, the total momentum before an interaction equals the total momentum after it; this principle explains outcomes of collisions and explosions.

The energy transferred to or from an object when a force acts on it and causes a displacement; work equals force times displacement when the force is parallel to the motion.

The energy an object possesses because of its motion, calculated as one-half the mass times the square of the speed; doubling the speed quadruples the kinetic energy.

Energy cannot be created or destroyed, only transformed from one form to another or transferred between objects; the total energy of an isolated system remains constant.

A disturbance that transfers energy from one place to another without transferring matter; waves can be mechanical, requiring a medium, or electromagnetic, which can travel through vacuum.

The number of complete wave cycles that pass a given point each second, measured in hertz; frequency is inversely related to wavelength for waves traveling at a fixed speed.

The bending of a wave as it passes from one medium into another where its speed changes; refraction explains why a straw appears bent in a glass of water.

For many conductors, the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, expressed as V = IR.

A circuit in which components are connected one after another so there is only one path for current; the same current flows through each component, and total resistance is the sum of resistances.

A circuit in which components are connected across the same voltage, providing multiple paths for current; the voltage across each branch is the same, and total current is the sum of branch currents.

The production of an electric current in a conductor by changing the magnetic field through it, or by moving the conductor through a magnetic field; this principle underlies generators and transformers.

The amount of heat energy needed to raise the temperature of one unit mass of a substance by one degree Celsius; water has a relatively high specific heat, so it resists rapid temperature change.

The smallest unit of an element that retains the chemical properties of that element; atoms consist of a nucleus containing protons and neutrons, surrounded by electrons.

A pure substance made of only one kind of atom, defined by its atomic number; elements cannot be broken down into simpler substances by ordinary chemical reactions.

A pure substance formed when two or more different elements are chemically bonded in fixed proportions; a compound has properties different from those of its constituent elements.

A combination of two or more substances that are not chemically bonded and can be separated by physical means; mixtures may be homogeneous, with uniform composition, or heterogeneous.

An atom or group of atoms that has gained or lost electrons, giving it a net positive or negative electric charge; ions form when atoms achieve a more stable electron arrangement.

One of two or more forms of the same element whose atoms have the same number of protons but different numbers of neutrons, and therefore different mass numbers.

The number of protons in the nucleus of an atom, which uniquely identifies the element; in a neutral atom, the atomic number also equals the number of electrons.

The electrons in the outermost shell of an atom that participate in chemical bonding; the number of valence electrons largely determines an element's chemical reactivity and bonding behavior.

A chemical bond formed by the electrostatic attraction between oppositely charged ions, typically when a metal transfers valence electrons to a nonmetal.

A chemical bond in which two atoms share one or more pairs of valence electrons; covalent bonds commonly form between nonmetal atoms and can be polar or nonpolar.

A process in which substances are transformed into different substances by breaking and forming chemical bonds; reactants are converted into products, often with energy changes.

In a closed system, the total mass of the reactants equals the total mass of the products in a chemical reaction, because atoms are neither created nor destroyed.

A counting unit used in chemistry equal to Avogadro's number, about 6.022 times 10 to the 23rd particles; one mole of a substance contains that many atoms, molecules, or formula units.

A scale from 0 to 14 that measures the concentration of hydrogen ions in a solution; values below 7 are acidic, 7 is neutral, and values above 7 are basic.

A substance that donates hydrogen ions or accepts electrons in a chemical reaction; acidic solutions have a pH below 7 and can react with bases to form salts and water.

A substance that accepts hydrogen ions or donates electrons in a chemical reaction; basic solutions have a pH above 7 and can react with acids to form salts and water.