Of the hard sciences, physics is definitely my favorite. Biology is the most relatable and chemistry is possibly the most practical, but physics is the most philosophical. What is energy? What is matter? What is reality? How did it all begin? We’ll be debating these questions for a very long time.
ESSENTIAL KNOWLEDGE: PHYSICS
Physics: The study of movement and energy, including the study of mechanics, gravity, electricity, sound, light, magnetism, nuclear energy, quantum mechanics and more
Energy: The massless, volumeless, invisible something that allows for movement, chemical change and work. Everything in the universe is either this or matter. It cannot be either created or destroyed; in order to get it out of a system, you must put it into the system in a different form. It is stored in wood, fuel, batteries, light, food, and much more.
Energy conversion: A change in the form of energy from one type to another. For example, during photosynthesis, sun energy becomes stored energy, then kinetic energy used for growth.
Energy chain: The sequence of energy conversions that happen when energy is transformed from one form to another, with each transformation leading to the next
Kinetic energy: Energy that is currently active, such as wind energy and the movement of water
Potential energy: Energy that is currently in storage, such as seed energy or the energy inside a full balloon
Solar energy: The light and heat energy whose source is the sun
Nuclear energy: The energy found in an atom’s nucleus
Thermal energy: The energy that results from something’s internal temperature
Heat energy: The energy that is transferred from a warmer object to a cooler object as a result of a temperature difference between the two objects. This kind of energy moves from a warmer place to a cooler place, like air pressure moves from high-pressure to lower-pressure places and like water flows downhill.
Chemical energy: The energy stored in the bonds between atoms in molecules
Electrical energy: The energy carried by the movement of electrons in an electric conductor
Mechanical energy: The total potential and kinetic energy something has due to its motion and/or position
Gravitational energy: The potential energy something has due to its position in a gravitational field. An example is an apple that has not yet fallen off the apple tree.
Force: Any push or pull on an object. This includes the force of gravity, the force of a human hand picking something up, and much more. There are four fundamental forces in the universe: the strong nuclear force, the weak nuclear force, the electromagnetic force, and gravity. Note that all objects not in motion still have forces acting on them at all times, but when not moving, these forces cancel each other out. For example, in order for a person to sit still they must hold their body upright in a way that perfectly balances the force of gravity on it.
The strong nuclear force: The force that holds an atom’s nucleus together
The weak nuclear force: The force responsible for the decay of neutrons and more
The electromagnetic force: The force responsible for electric and magnetic interactions
Gravity: The force everywhere in the universe that pulls every object towards every other object simultaneously. This includes planets, stars, galaxies, electrons and even light. It holds heavenly bodies in orbit around each other; causes planets to attract particles and grow larger; causes the Moon to pull Earth’s water toward it, creating tides; gives things on Earth weight; and more. The greater the mass an object has, the greater gravitational force it exerts. It is the weakest of the four fundamental forces.
Albert Einstein’s General Theory of Relativity: The scientific theory that states that gravity is not a true force, but the simple physical result of the curvature of spacetime which in turn is caused by the uneven distribution of mass across the universe
E=mc^2: Energy equals mass times the speed of light squared. This is the formula that Einstein discovered that shows that a small amount of mass can be converted into a large amount of energy, and vice versa, as long as the speed of light is involved in the process.
Dynamics: The study of how forces affect motion
Fluid dynamics: The scientific principles that explain the flow of liquids and gases
Velocity: The speed of something in a given direction. It changes when direction changes even when speed stays the same.
Terminal velocity: The maximum velocity something reaches while in freefall. When something falls through gas or liquid it accelerates at a decreasing rate until the force of gravity equals the forces of friction and it reaches this state.
Friction: The resistance of one surface to the motion of another. This phenomenon is everywhere, and without its effects, nothing would stop moving until an outside force acted on it.
Equilibrium: The physical state that exists when forces or energies or systems are in balance, and there is therefore no change in motion
Inertia: The property of matter by which a stationary object remains stationary or a moving object remains moving until acted upon by another force
Freefall: The physical state that occurs when gravity is the only force affecting an object
Weightlessness: The physical state that occurs when the effects of gravity are balanced out by other forces, such as the centrifugal force of a spacecraft, and therefore seems to have no effect
Centripetal force: The force that causes something to turn in a circular path instead of in a straight line. It is not a fundamental force itself, but the net result of all the forces acting on the object that result in the circular movement.
Cohesion: The physical state that exists when molecules of a certain substance are more attracted to each other than to the substance they’re touching. An example is surface tension.
Adhesion: The physical state that exists when molecules are more attracted to the substance they’re touching than to each other. An example is glue on paper.
Diffusion: The spreading out of molecules to fill a space more evenly. An example is the spreading out of perfume to fill the air in a room.
Surface tension: The physical state that exists when a liquid’s surface resists gravity somewhat, remaining cohesive. This happens because the molecules in water at top are more attracted to the molecules in the water below than to the molecules in the air.
Turbulence: The uneven movement caused when an object moves through air or water
Drag: The friction that occurs on an object moving through air. With no friction at all, objects falling toward the earth would fall at the same rate.
Air compression: The condition created when air particles are pushed closer together (as in a small space such as a tire or a balloon). When this happens, the particles try to escape and expand by pushing on the inside walls, causing visible inflation.
Vacuum: An area of decreased air pressure that causes areas of higher air pressure to be drawn towards it. It is created when gases, such as air, are removed from a space. An example is outer space, which has no air. It isn’t isn’t the motion of pulling out air that causes it to draw air towards it, but the natural physical reaction of higher-pressure air to rush to fill (and thus balance out) lower-pressure air that causes this behavior.
Newton’s First Law of Motion: “A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force.”
Newton’s Second Law of Motion: “The force acting on an object is equal to the mass of that object times its acceleration.”
Newton’s Third Law of Motion: “For every action, there is an equal and opposite reaction.” An example of this occurs when a balloon full of air is let go: the air goes one way and the balloon goes another.
Electricity: The effect caused by the presence and movement of charged particles (specifically, the electrons in the charged particles)
Electromagnetism: The force of electricity and magnetism, which occurs when electrically charged particles interact with an electromagnetic field
Electromagnetic spectrum: All types of electromagnetic radiation, whether or not they are visible to the human eye, including (in order): gamma rays, X-rays, ultraviolet rays, visible light, infrared rays, microwaves, radio waves (such as those used for radar, FM, TV, shortwave and AM) and more
Electromagnetic waves: Waves made of continually changing electric and magnetic fields that can move through solids, liquids, gases and even a vacuum
Electric field: An area that surrounds an electric charge or an electromagnetic wave that exerts force on other charges
Electric current: A flow of electric charge through a material or along a conductor
Conductor: An object or material that allows an electrical current to flow in one or more directions
Insulator: An object or material that does not allow an electrical current to flow freely or easily through it
Semiconductor: An object or material with some conduction, but not as much as a true conductor has
Static electricity: Electricity created due to an imbalance of electrical charges that causes some charges to seek a path away from their present location
Magnet: A material or object that produces a magnetic field. All of these have five properties in common: they only act on certain materials (iron, cobalt and nickel); they have two poles; their opposite poles attract and their like poles repel; they have magnetic fields; and their magnetic fields pass through other materials.
Magnetic field: The space around a magnet, which can attract or repel certain materials such as iron, cobalt, or nickel. It is strongest at the poles. The earth is a large magnet, and its field is strong enough that magnets will reorient to be parallel to it, which is why compasses work.
Magnetic poles: The two ends of a magnet, one of which is north-seeking and one of which is south-seeking. Opposite ends attract each other and like ends repel each other. Note that the earth’s poles don’t correspond exactly to the geographical North Pole and South Pole.
Ferromagnetism: The magnetic quality of certain materials (such as iron, cobalt and nickel) that allows these materials to permanently attract or repel. There are also many other materials that have a magnetic quality, but more weakly and not permanently.
Light: A form of energy made up of electromagnetic waves
Visible light spectrum: The relatively small part of the light spectrum that is visible to the human eye
Speed of light: The speed that light travels in a vacuum: over 186,000 miles per second. It is also the highest possible speed at which all other massless particles can travel, including gravitational waves and electromagnetic energy. Particles with any amount of mass can never reach this speed.
Luminosity: A measurement denoting the total amount of light energy emitted, whether the object is luminous itself or merely reflecting light, such as the moon
Transparent: See-through
Translucent: Almost entirely see-through
Opaque: Not see-through
Umbra: The darkest part of a shadow
Penumbra: The faded part of a shadow
Color: The various visual effects that occur when different types of matter absorb some wavelengths of light and reflect others. Wavelengths that are reflected are perceived by the human eye, while wavelengths that are absorbed are not perceived, which creates color variation.
Fluorescence: The ability to glow when exposed to light, which occurs when the material absorbs high-frequency wavelengths, like UV light (which is invisible to the human eye), then emits lower-frequency visible light as a response. UV light works best to create the glow effect because some energy is lost in the energy conversion process, and UV light has a high-energy frequency.
Phosphorescence: The ability to store fluorescent energy, then emit it up to several hours after the absorption
Convex lens/converging lens: A lens that is shaped like an upside-down bowl, whose center is thicker than its edges, which causes light to bend towards the center, making objects appear larger than they actually are. This kind of lens corrects farsightedness.
Concave lens/diverging lens: A lens that is shaped like a bowl, whose center is thinner than its edges, which causes light to bend away from the center, making objects appear smaller than they actually are. This kind of lens corrects nearsightedness.
Mirror: A piece of glass or other transparent material with a silver-colored backing behind it that causes all light to reflect back to the viewer
Reflection: The bouncing back of light rays from a surface
Refraction: A change in the path of a light wave as it passes from one medium to another. For example, a straw placed in a glass of water appears bent due to the changing path of light when traveling through air versus through water.
Diffraction: The bending and spreading out of light waves, as when passing through small openings or encountering an obstacle
Dispersion: The splitting of visible light into its component colors, which is what makes it possible for the eye to see individual colors, as in a rainbow
Prism: A transparent object, such as a diamond or a piece of cut glass, that bends light that hits it, thereby splitting it and causing a rainbow to appear
Interference: A change in the paths, amplitudes and/or frequencies of two waves as they interact with each other. When the peaks and troughs of waves that meet line up with each other, the wave increases in size. When the peaks and troughs of waves that meet are placed opposite of each other, the wave decreases in size.
Sound: The vibration that occurs in a hearing ear after sound waves transfer energy through the particles in the air until making contact with that ear. Unlike light waves, which travel as electromagnetic radiation, this type of wave transfers movement energy through gases, liquids or solids. That means it can’t travel through a vacuum such as space, and that it travels much more slowly than does light.
Tone: A prolonged sound note that vibrates at a steady frequency
Frequency: The speed of a sound’s vibration, with faster vibrations creating higher frequencies and slower vibration creating lower frequencies
Pitch: The perceived highness or lowness of a sound note depending on its frequency. It is made by tightening or loosening vocal cords, guitar strings, etc., thereby slowing down or speeding up the sound vibrations.
Sound intensity: The loudness of a sound. Louder sounds have more energy and lower sounds have less energy.
Amplitude: The length of a sound wave from top to bottom. The longer the sound wave, the louder the sound.
Decibel: A unit of measurement of loudness
Infrasound: Sounds at frequencies below the ability of humans to hear it
Ultrasound: Sounds at frequencies above the ability of humans to hear it
Supersonic: Exceeding the speed of sound
Subsonic: Not exceeding or equal to the speed of sound
Sonic boom: The shock wave produced when an object moves through the air faster than the speed of sound
Sound barrier: The apparent physical boundary stopping the forward progress of an object traveling through the air at or above the speed of sound
Echo: The reflection of sound waves off a surface, resulting in a delayed repetition of the original sound
Sonar: A technique for locating objects underwater by bouncing high-frequency sound waves off of them
Convection: The transfer of heat through the movement of gases or liquids, such as ocean currents or warm air currents
Conduction: The transfer of heat through solids using direct contact, such as a pan on a burner
Radiation: The transfer of heat through the air or through space, such as the sun heating the atmosphere or a radiator heater heating a home’s air, whether or not that air is moving
Theoretical physics: A branch of physics that relies on mathematical models to explain natural phenomenon, rather than on applied experiments
String theory: The scientific theory proposing that the fundamental particles that make up the universe are not particles or matter, but instead string-shaped vibrations
Quantum theory: The scientific theory that attempts to explain wave-particle duality, quantization of energy, entanglement and other phenomenon found at the subatomic level
The theory of everything: Any theory that attempts to explain how all of the different theories, laws and forces can work together in the same universe, even though at times they seem to contradict each other. Note that since general relativity is used for large-scale problems and quantum theory is used for small-scale problems, their incompatibility is usually avoided in practical matters of science.
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