MCAS Grade 8 Science key terms

The amount of matter in an object, measured in grams or kilograms. Mass stays the same regardless of location, unlike weight, which changes with gravitational pull.

The force of gravity acting on an object's mass, measured in newtons. An object's weight changes if gravitational strength changes, such as on the Moon versus Earth.

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

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

Anything that has mass and takes up space. Matter exists as solids, liquids, and gases, and is made of atoms and molecules that are always in motion.

The smallest unit of an element that keeps the element's properties. It contains protons and neutrons in a central nucleus, with electrons moving around it.

Two or more atoms chemically bonded together, such as two hydrogen atoms joining one oxygen atom to form water. Molecules can be made of the same or different elements.

A pure substance made of only one kind of atom that cannot be broken down into simpler substances by ordinary chemical means. Examples include oxygen, iron, and carbon.

A substance formed when atoms of two or more different elements bond chemically in a fixed ratio, such as water or table salt. It has properties unlike its elements.

A chart organizing all known elements by increasing atomic number, with elements in columns sharing similar chemical properties. It shows each element's symbol and atomic mass.

The number of protons in an atom's nucleus, which identifies the element. In a neutral atom it also equals the number of electrons.

A change in a substance's appearance, shape, or state without forming a new substance, such as melting ice or tearing paper. The chemical identity stays the same.

A process in which substances break apart or combine to form new substances with different properties. Evidence includes color change, gas production, heat release, or precipitate formation.

A starting substance in a chemical reaction that is used up as new substances form. Reactants appear on the left side of a chemical equation.

A new substance formed by a chemical reaction. Products appear on the right side of a chemical equation and have properties different from the reactants.

The principle that matter is neither created nor destroyed in a chemical reaction or physical change. The total mass of reactants equals the total mass of products.

A change between solid, liquid, and gas states caused by adding or removing heat energy, such as melting, freezing, evaporation, or condensation. It is a physical change.

The energy of motion. Particles of matter have kinetic energy that increases with temperature, causing them to move faster and spread farther apart.

Stored energy based on an object's position or condition, such as a ball held above the ground or energy stored in chemical bonds. It can convert to kinetic energy.

A push or pull that can change an object's motion, direction, or shape, measured in newtons. Forces have both size and direction and can combine or cancel.

The overall force on an object after all individual forces are combined. A nonzero net force changes motion; a zero net force means forces are balanced.

Forces equal in size and opposite in direction that cancel each other out. An object with balanced forces stays at rest or keeps moving at constant speed in a straight line.

Forces that do not cancel because their combined effect is nonzero. They cause an object to start moving, stop, speed up, slow down, or change direction.

A force that opposes motion when two surfaces touch, converting kinetic energy into heat. Its strength depends on the surfaces and how hard they press together.

A force of attraction between objects with mass. On Earth it pulls objects downward with an acceleration of about 9.8 meters per second squared.

The tendency of an object to resist changes in its motion. Objects with greater mass have greater inertia, so they are harder to speed up or slow down.

How fast an object moves, calculated as distance divided by time. It describes magnitude only, not direction, and is often measured in meters per second.

Speed in a specific direction, such as 5 meters per second north. A change in either speed or direction means velocity changes, which counts as acceleration.

The rate at which velocity changes over time, including speeding up, slowing down, or changing direction. It results from an unbalanced force acting on a mass.

The movement of energy from one object or system to another, such as heat flowing from a hot object to a cooler one. Energy changes form but is never lost.

The total kinetic energy of all particles in a substance. Adding heat increases thermal energy and temperature, while removing heat decreases both.

Heat transfer through direct contact between materials, as when a metal spoon warms in hot soup. Energy passes from faster-moving particles to slower ones.

Heat transfer by the movement of fluids, where warmer, less dense material rises and cooler, denser material sinks. It drives ocean currents and weather patterns.

Heat transfer by electromagnetic waves, which can travel through empty space. Sunlight warming Earth is an example of energy moving by radiation.

The upward force a fluid exerts on an object placed in it. An object floats when the buoyant force equals its weight, which depends on relative density.

The distance between two matching points on consecutive waves, such as from crest to crest. It relates to a wave's energy and color of light.

The number of wave cycles that pass a point each second, measured in hertz. Higher frequency means more energy and, for light, a shift toward blue.

The maximum distance a wave moves from its resting position, indicating the wave's energy. For sound, larger amplitude means a louder sound.

A repeating disturbance that transfers energy from place to place without carrying matter along. Waves can be mechanical, needing a medium, or electromagnetic, traveling through space.