4th Grade Glossary
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acid rain A mild acid solution formed when rain mixes with sulfur dioxide and nitrogen oxides in the air

4th Grade SCIENCE Glossary



acid rain: A mild acid solution formed when rain mixes with sulfur dioxide and nitrogen oxides in the air.

Contributes to the chemical weathering of certain kinds of rocks and minerals.


adaptation: A structure or behavior that helps an organism survive and reproduce in its environment.


alluvial fan: A triangular-shaped landform created when deep, fast-moving water enters a wide, shallow area, slows down, and deposits its sediment. Similar to a delta but forms upstream


Alpha Centauri: A three star system, the closest to Earth.


animal: A living being capable of movement and motor response to stimulation.


armature: The coil(s) of wire in an electric motor that rotate through the magnetic fields of permanent magnets.


average distance: A measurement used to calculate the difference in distance between planets.


axis: An imaginary line, or axle, through the center of an object, about which the object rotates.



base level: The level at which a stream or river enters a lake or ocean. The mouth of a stream or river is at its base level.


biceps: The large muscle at the front of the upper arm.


breakwater: An artificial barrier constructed along the shoreline to absorb or deflect the energy of waves, thereby reducing erosion.


brush: The device in an electric motor that transfers the electric current from the batteries to the coils of the armature by brushing up against the lead wires.



carrying capacity: The greatest number of organisms of one kind that can survive in an area.


cell: The tiny structures of which all living


centimeter: A unit of length equal to one hundredth of a meter.




chemical weathering: The process of breaking down Earth’s surface by changing the chemical composition of rocks and minerals(for example, by acid rain or oxidation).


chlorophyll: The green pigment in plants that allows them to photosynthesize.


chromosome: A structure that contains an organism’s genes; located in cells.



data: Information collected in an experiment.


day: The length of time a planet takes to make one complete rotation about its axis.


delta: A landform created when a river or stream reaches its base level, slows down, and deposits its sediment; named after the Greek letter delta (Δ) from its shape.


dependent variable: The variable in an experiment that changes in response to

changes in the independent variable.


deposition: The process in which particles settle to the bottom of a liquid; the release of sediment

that occurs when a fast-moving river or stream slows down.


diaphragm: The muscle that separates the chest cavity from the abdominal cavity.


dike: A barrier of earth erected to keep a river or stream from overflowing its banks. See also levee.


dominant gene: A gene that masks, or overpowers, a recessive gene; a dominant gene is expressed when it is paired with a recessive gene. See also recessive gene.


driven gear: The gear receiving the force.


driving gear: The gear transmitting the force.


dune: A mound of windblown sand resulting from the constant erosion and deposition of sand by wind.



Earth: The third planet from the Sun in our Solar System.


electromagnet: A magnetic system consisting of a ferrous object surrounded by coils of wire that have electric current flowing through them.


energy: The ability to do work or to bring about change in a system or the surroundings.


environment: The area where a plant or animal lives.


equator: The imaginary line that divides Earth in half between the North and South Poles.


erosion: The carrying away of weathered material by wind, water, or glaciers.


extensor: A muscle that straightens out a body part.



femur: The thighbone, extending from the pelvis to the knee.


fibula: The smaller of the two bones forming the lower leg.


flexor: A muscle that bends a body part.


floodplain: The broad, flat, low-lying land around rivers and streams subject to occasional flooding.


flower: The plant structure that makes seeds in flowering plants.


force: A push on an object; measured in newtons


fruit: A plant structure that surrounds and protects the seeds.



galaxy: One of countless swirling, massive clusters of solar systems in the universe.


gear: A wheel with teeth that, when meshed with the teeth of another wheel, is able to transmit, modify, or change the direction. of an applied force.


gear ratio: The ratio of the number of rotations of the driving gear to the driven gear.


gene: Tiny structures within cells that contain the information for a trait.


germinate: To sprout and begin to grow into a seedling.


gravitational attraction: The force of gravity that causes objects to be attracted to one another.


gravity: The attractive force that exists between objects.



home range: The area where a population of animals usually forages for food.


humerus: The bone in the upper arm, connecting the elbow to the shoulder.



hypothesis: An educated guess about what the answer to the stated problem in an

experiment might be.


independent variable: The variable that is not held constant in an experiment.


inherited: Passed from parents to children.



joint: The place where two adjoining bones meet.


joule: A unit of work; 1 joule of work is performed when a force of 1 newton is used to move an object a distance of 1 meter.


Jupiter: The fifth planet from the Sun in our Solar System.



levee: A continuous dike; may be human- made or natural.


leaf: A plant structure that uses the energy in sunlight to make food.


light-year: A unit of distance, equal to the distance light travels in a year—about9.46 trillion km.


lungs: The basic respiratory organ of vertebrates.



mandible: The lower jaw bone.


map: A scale drawing used to represent geographic locations and their relative distances from one another.


Mars: The fourth planet from the Sun in our Solar System.


mass: The measure of the amount of material an object contains.


meander: A curve or bend in a streambed or riverbed formed by slow-moving water on

gently sloping land.


mechanical energy: Physical energy, as opposed to chemical energy.


Mercury: The planet closest to the Sun in our Solar System.


meter: The international standard unit of length.


Milky Way: The galaxy of which our Solar System is a member.


millimeter: A unit of length equal to one thousandth of a meter.


mnemonic device: A memory aid, such as a made-up sentence or rhyme, that helps recall the order of items in a list.


moon: A satellite of a planet.


motor: An electromechanical device by which electric energy is transformed into mechanical energy


muscle: Body tissues that function in movement.


muscular system: All the muscles in our body including muscles that move our limbs and heart.



Neptune: The eighth planet from the Sun in our Solar System.


newton: The international unit of force.


North Star (Polaris) : The star almost directly above the north pole of the Earth


Northern Hemisphere: The half of Earth that is located north of the equator.



orbit: The elliptical path that a satellite travels as it moves around a star or a planet.


oxidation: The chemical reaction of rusting that occurs when certain substances are exposed to the oxygen in air. Oxidation contributes to the chemical weathering of certain kinds of rocks and minerals.



particle: A small bit of material.


patella: The kneecap.


pelvis: The hip bone.


permanent magnet: A material exhibiting a magnetic field, regardless of its environment.


physical weathering: The mechanical breakdown of rocks and minerals (for example, by wind, water, ice, changes in temperature, and plant roots).


planet: A large, spherical satellite of a star.



plant: A living thing that produces its own food and typically lacks locomotive movement or obvious sensory organs.


Pluto: A dwarf planet in our Solar System.


population: A group of organisms of one kind that lives in the same area.


producer: Green plants that can produce food from sunlight, carbon dioxide, and water.



radius: The bone of the inner forearm.


ratio: A numerical representation of a relationship between two measurements, as in a scale for a drawing or a model.


recessive gene: A gene that is not expressed when it is paired with a dominant gene. See also dominant gene.


relative brightness: The brightness of an object when compared with the brightness of surrounding objects


relative distance: The distance between objects when compared with the distance between surrounding objects.


relative size: The size of an object when compared with the size of surrounding objects


respiratory system: Includes the lungs, trachea, bronchi, and the channels leading to the mouth and nose; handles the body’s air supply.


revolution: One complete orbit of a satellite.


revolve : To travel around another object.


rib: One of a series of bones surrounding the chest cavity of the body.


root: A plant structure that holds a plant in place and takes in water and nutrients from the soil.


rotation: One complete turn of a satellite about its axis.


runoff: Running water from rain or melting snow that has not evaporated and has not been absorbed by the ground.



satellite: An object in orbit around a larger object.


Saturn: The sixth planet from the Sun in our Solar System.


scale: A proportion used in determining the relationship between two measurements of size or distance.


scale drawing: A two-dimensional scaled representation of a smaller or larger object.


scapula: The shoulder blade.


season: A short-term weather condition that repeats on a regular basis.


sediment: Earth materials (sand, soil, rocks) carried away by moving water and deposited when the water slows down.


seed: A plant structure that contains a tiny new plant and a supply of food for the plant.


series circuit: A single path by which current can flow through an electric circuit.


skeletal system: The bones that provide support for the body, protection for internal organs, and places of attachment for muscles.


skeleton: All the bones that make up the supportive structure in the body of an animal


slope: The incline (upward or downward slant) of terrain.


solar system: A star and all the satellites that orbit it.


Southern Hemisphere: The half of Earth that is located south of the equator.


star: An extremely large, hot ball of glowing gas that radiates light and heat.


stem: A plant structure that holds the leaves up to sunlight and moves food, water, and nutrients around the plant.


sternum: The breastbone.


Sun: The star of our Solar System.


system :An interdependent group of items that form a unified whole.



tendon: The tissue that connects muscle to bone.


tibia: The larger of the two bones making up the lower part of the leg.



tidal action (tide): The periodic change (rise and fall) of the surface of the oceans caused by the gravitational pull of the moon.


trachea: The windpipe.


trait: A physical or behavioral characteristic of an organism.


triceps: The large muscle at the rear of the upper arm.



ulna: The bone of the outer forearm.


universe: The vast space that surrounds and includes all the galaxies as well as all other existing matter and energy


Uranus: The seventh planet from the Sun in our Solar System.



variable: Any factor that can change in an experiment.


Venus: The second planet from the Sun in our Solar System.


vertebra: One of the bones comprising the backbone.



wave: A rhythmic rise and fall of the water’s surface commonly caused by the wind.


weathering: The slow process of breaking down rocks and minerals on Earth’s surface. See also chemical weathering and physical weathering.


windbreak: A natural or artificial barrier that reduces erosion caused by wind.


work: The transfer of energy resulting from a force acting to move an object over a distance.

Work = Force × distance.



year: The length of time a planet takes to make one complete revolution around the Sun.