Science (US Middle School)
Integrated science deck for US middle school students (grades 6-8) aligned with NGSS Middle School standards. Covers Physical Science, Life Science, Earth and Space Science, and Engineering Design.
Ämne: Naturkunskap · Nivå: Högstadium (13–15) · 478 kort
Innehåll
- An atom is the smallest unit of matter that retains the chemical properties of an element. It consists of a nucleus containing protons and neutrons, surrounded by electrons.
- An element is a pure substance made of only one type of atom. There are about 118 known elements, arranged in the periodic table.
- A molecule forms when two or more atoms bond together. Examples include H₂ (two hydrogen atoms), O₂, and H₂O (water).
- A compound is a substance made of two or more different elements chemically bonded in a fixed ratio. Water (H₂O) and carbon dioxide (CO₂) are compounds.
- Protons have a positive charge, electrons a negative charge, and neutrons have no charge. The number of protons determines which element an atom is.
- The four common states of matter are solid, liquid, gas, and plasma. Each differs in how tightly its particles are packed and how much they move.
- In a solid, particles vibrate in fixed positions. In a liquid, particles flow past each other. In a gas, particles move freely and fill any container.
- Phase changes are reversible physical changes: melting (solid → liquid), freezing, evaporation (liquid → gas), condensation, sublimation (solid → gas), and deposition.
- Mass is the amount of matter in an object, measured in grams or kilograms. Weight is the force of gravity on that mass and changes depending on location.
- Density is mass per unit volume (ρ = m/V). An object floats in a fluid if its density is less than the fluid’s; it sinks if greater.
- A physical change alters appearance or state but not chemical identity (e.g., ice melting). A chemical change creates new substances (e.g., wood burning).
- The law of conservation of mass says matter is neither created nor destroyed in a chemical reaction. Atoms are only rearranged, so total mass stays constant.
- In a chemical reaction, the substances you start with are reactants and the substances produced are products. Bonds break and new bonds form.
- Signs of a chemical reaction include color change, temperature change, gas production (bubbles), light or sound, and formation of a precipitate (solid).
- An exothermic reaction releases energy as heat or light (e.g., combustion). An endothermic reaction absorbs energy from its surroundings (e.g., baking soda + vinegar).
- The pH scale runs from 0 to 14. Acids have pH less than 7, bases have pH greater than 7, and pure water has a neutral pH of 7.
- Speed is distance divided by time (v = d/t). Velocity is speed in a specific direction, so it is a vector quantity.
- Acceleration is the rate at which velocity changes over time. An object speeds up, slows down, or changes direction when it accelerates.
- A force is a push or pull. Forces are measured in newtons (N) and can change an object’s speed, direction, or shape.
- When forces on an object are balanced, the net force is zero and motion does not change. Unbalanced forces cause acceleration.
- Newton’s first law (inertia): an object at rest stays at rest, and an object in motion stays in motion in a straight line, unless acted on by an unbalanced force.
- Newton’s second law: F = m×a. The net force on an object equals its mass times its acceleration. Heavier objects need more force to accelerate.
- Newton’s third law: for every action there is an equal and opposite reaction. Pushing on a wall pushes you back; a rocket pushes gas down, gas pushes the rocket up.
- Gravity is the attractive force between any two objects with mass. Earth’s gravity pulls objects toward its center with an acceleration of about 9.8 m/s².
- The strength of gravity depends on mass and distance. Larger masses pull harder; objects far apart pull less. Gravity follows an inverse-square law with distance.
- Friction is a contact force that opposes motion between two surfaces. It changes some kinetic energy into thermal energy (heat).
- Energy is the ability to do work or cause change. It comes in many forms: kinetic, potential, thermal, chemical, electrical, light, sound, and nuclear.
- Kinetic energy is the energy of motion: KE = ½ m v². Faster or heavier objects have more kinetic energy.
- Potential energy is stored energy due to position or condition. Gravitational potential energy depends on height (PE = m×g×h).
- The law of conservation of energy says energy can be transferred or transformed but never created or destroyed. The total energy in an isolated system stays constant.
- Thermal energy is the total kinetic energy of all the particles in a substance. The hotter something is, the faster its particles move.
- Heat is the transfer of thermal energy from a hotter object to a cooler one. Heat can move by conduction, convection, or radiation.
- Conduction transfers heat through direct contact. Convection transfers it through fluid motion (warm air or water rises). Radiation transfers heat via electromagnetic waves.
- Temperature measures the average kinetic energy of particles, not the total. A small cup of boiling water has the same temperature as a kettle full, but less thermal energy.
- A wave is a disturbance that transfers energy without transferring matter. Waves move through a medium (water, air, solids) or, for light, through empty space.
- Wavelength is the distance between two crests (or troughs) of a wave. Amplitude is how far the wave moves from its rest position — it shows the energy carried.
- Frequency is the number of waves passing a point per second, measured in hertz (Hz). Higher-frequency waves carry more energy in light and have higher pitch in sound.
- Sound is a longitudinal mechanical wave caused by vibrating particles. It needs a medium (gas, liquid, or solid) and cannot travel through a vacuum.
- Light is part of the electromagnetic spectrum. Visible light is only a tiny slice; the spectrum also includes radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
- Light travels at about 300,000 km/s in a vacuum. Unlike sound, it does not need a medium and can cross empty space — which is why we see distant stars.
- Light can be reflected (bounces off), refracted (bends as it changes medium), or absorbed. Mirrors reflect; lenses and water refract; dark surfaces absorb.
- The visible spectrum of light contains the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet (ROYGBIV). Red has the longest wavelength, violet the shortest.
- The cell is the basic unit of life. All living things are made of one or more cells, and all cells come from existing cells (cell theory).
- Prokaryotic cells (like bacteria) have no nucleus or membrane-bound organelles. Eukaryotic cells (plants, animals, fungi, protists) do have a nucleus and complex organelles.
- The cell membrane controls what enters and exits the cell. It is selectively permeable: water and small molecules pass easily, larger ones are restricted.
- The nucleus contains the cell’s DNA and controls activities like growth, metabolism, and reproduction. It is surrounded by a nuclear membrane.
- Mitochondria are the powerhouses of the cell. They use oxygen and glucose to perform cellular respiration, producing ATP — the cell’s usable energy.
- Chloroplasts are found in plant cells and contain chlorophyll. They capture sunlight and use it to produce sugar through photosynthesis.
- The cell wall is a rigid layer outside the membrane of plant, fungal, and bacterial cells. It gives shape and structural support; animal cells do not have one.
- Ribosomes are tiny structures inside a cell that build proteins by linking amino acids in the order specified by RNA.