GA Milestones Science Grade 8 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Density formula

Density equals mass divided by volume. It tells how much matter is packed into a given space and determines whether an object floats or sinks in a fluid.

Buoyancy

The upward force a fluid exerts on an object placed in it. An object floats when the buoyant force equals its weight, which happens when its density is less than the fluid's.

Newton's first law

An object at rest stays at rest and an object in motion keeps moving in a straight line at constant speed unless a net force acts on it.

Newton's second law

The acceleration of an object equals the net force on it divided by its mass, written F = m × a. Greater force or smaller mass produces greater acceleration.

Newton's third law

For every action force there is an equal and opposite reaction force. The two forces act on different objects, which is why they do not cancel out.

Net force

The single force obtained by combining all forces acting on an object. If forces are balanced the net force is zero; if unbalanced the object accelerates in the direction of the net force.

Speed versus velocity

Speed is distance divided by time and has no direction. Velocity is speed in a stated direction, so a change in direction is a change in velocity even at constant speed.

Acceleration

The rate at which velocity changes over time. An object accelerates when it speeds up, slows down, or changes direction, and acceleration is measured in meters per second squared.

Kinetic energy

The energy of motion, calculated as one-half mass times velocity squared. Doubling speed increases kinetic energy four times because velocity is squared.

Potential energy

Stored energy based on position or condition. Gravitational potential energy equals mass times gravity times height, so raising an object increases its stored energy.

Conservation of energy

Energy cannot be created or destroyed, only transferred or transformed between forms. In any system, the total energy before and after a change stays the same.

Series circuit

A circuit with only one path for current. Current is the same at every point, and if the path breaks anywhere, all devices in the circuit stop working.

Parallel circuit

A circuit with two or more separate paths. Current splits among branches, voltage across each branch is equal, and one broken branch does not stop the others.

Electrical resistance

The opposition to current flow in a material. Longer, thinner, or hotter wires have more resistance, and resistance converts electrical energy into heat.

Conductors and insulators

Conductors, such as copper and aluminum, allow charge to flow easily because electrons move freely. Insulators, such as rubber and glass, resist charge flow and are used to protect people.

Wave frequency

The number of wave cycles passing a point each second, measured in hertz. Higher frequency means more cycles per second and, for a given speed, a shorter wavelength.

Wave speed relationship

Wave speed equals frequency multiplied by wavelength. If speed stays constant, increasing frequency decreases wavelength and decreasing frequency increases wavelength.

Transverse versus longitudinal

In transverse waves the disturbance is perpendicular to wave travel, as in light. In longitudinal waves the disturbance is parallel, creating compressions and rarefactions, as in sound.

Law of conservation of mass

In a chemical reaction, atoms are rearranged but not created or destroyed, so the total mass of reactants equals the total mass of products in a closed system.

Physical versus chemical change

A physical change alters size, shape, or state without forming a new substance. A chemical change produces new substances with different properties, such as burning or rusting.

Chemical reaction evidence

Signs of a chemical reaction include a new color, gas bubbles, a precipitate forming, a temperature change, or light given off. These indicate new substances formed.

Element, compound, mixture

An element is one kind of atom; a compound is two or more elements chemically bonded; a mixture contains substances combined physically and separable by physical means.

Atoms and molecules

An atom is the smallest unit of an element retaining its properties. A molecule is two or more atoms bonded together, such as water made of two hydrogen atoms and one oxygen atom.

Periodic table organization

Elements are arranged by increasing atomic number. Rows are periods and columns are groups; elements in the same group share similar chemical properties because of similar outer electron patterns.

Earth's layers

From outside inward: crust, mantle, outer core, and inner core. The crust is thin and rocky, the mantle is hot and slowly flowing, and the core is mostly iron and nickel.

Plate tectonics

Earth's lithosphere is broken into plates that move over the mantle. Their collisions, separations, and slides cause earthquakes, volcanoes, and mountain building.

Rock types

Igneous rock forms from cooled magma or lava, sedimentary rock forms from compacted sediments, and metamorphic rock forms when heat and pressure change existing rock.

Weathering and erosion

Weathering breaks rock into smaller pieces in place by water, wind, ice, or chemicals. Erosion moves those pieces elsewhere, and deposition drops them to form new landforms.

Water cycle

Continuous movement of water through evaporation, condensation, precipitation, and runoff. The sun supplies the energy, and gravity drives precipitation and water flowing downhill.

Conduction, convection, radiation

Heat transfers by conduction through direct contact, by convection through moving fluids, and by radiation through electromagnetic waves that can travel through space.

Earth's seasons

Seasons result from Earth's tilted axis as it orbits the sun, which changes the angle and duration of sunlight. Distance from the sun is not the main cause of seasons.

Moon phases

The changing appearance of the moon as it orbits Earth, caused by the changing angle between the sun, Earth, and moon. A full cycle takes about 29.5 days.