School in a Book: Physics

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.


Physics: The study of movement and energy. This includes the study of gravity, electricity, sound, light, magnetism, nuclear energy and more.

Energy: The invisible, indescribable, mysterious thing that allows for movement and work. Energy is not made of particles and doesn’t have mass or volume. We cannot directly observe it, but only understand it through its effects. Note that everything in the Universe is made of either matter or energy. Note also that energy cannot be either created or destroyed; in order to get energy out of a system, you must first get it from somewhere else and put it in to the system. (It can convert into a different form, however.)

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 chain reaction that occurs as energy is converted to another form, then that energy is converted to another form, and so on.

Energy storing materials: Energy is stored in wood, fuel, batteries, light, food, etc.—anything that releases energy when burned. (Remember, food isn’t turned into energy. It stores energy, then releases it from the food.)

The two fundamental forms of energy: Potential and kinetic

Kinetic energy: Energy that is currently active, such as wind energy and the movement of water.

Potential energy: Energy currently in storage, such as seed energy or the energy inside a full balloon. In order to have potential energy, the material must be in a position to be affected by a force, such as gravity.

Solar energy: The light and heat that radiates from the sun

Nuclear energy: The energy found in an atom’s nucleus

Radiant energy:

Heat energy: A form of energy that flows from one place to another because of a difference in temperature. It is really the motion of the particles that feel hot. (So in a way it’s kinetic energy.) Heat energy flows from hot to cool to even out, like air pressure moves from high to low and water flows downhill.

Chemical energy: Energy stored in the bonds of atoms and molecules. It is released in chemical reactions in the form of heat.

Electrical energy: The energy carried by electrons in an electric conductor.

Mechanical energy: The energy something has due to its motion

Thermal energy: The energy something has due to its heat levels (temperature)

Gravitational energy: The energy something has due to the effects of its gravitational field. Example: A raised hammer has gravitational energy that is converted to heat energy after it lowers and hits the nail.

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. All objects not in motion still have forces acting on them at all times, but when not moving, these forces are canceling each other out. For example, in order to sit still I must hold my body upright in a way that perfectly balances the force of gravity on it.

The four fundamental forces in the universe: The strong force (the nuclear force that holds subatomic particles together), the weak force (gravity, which is much less powerful than the strong force), the electromagnetic force, and the weak interaction (the force responsible for the radioactive decay of atoms).

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. Gravity is what caused the planets to attract more particles and structures and grow larger. It holds heavenly bodies in orbit around each other, it causes the Moon to pull Earth’s water toward it, creating tides, and it gives things on Earth weight. The greater the mass an object has, the greater gravitational force it exerts.It is sometimes called the “weak force,” (referring to the four fundamental forces of physics) even though it is not actually a force at all.

Albert Einstein’s General Theory of Relativity: Gravity is not a force. It is not energy. It is a simple result of the curvature of spacetime which in turn is caused by the uneven distribution of mass across the universe.

E=mc2: Energy equals mass times speed of light squared. This is the formula that Einstein discovered that shows the rate at which matter is converted into energy and vice versa.

Dynamics: The study of how forces affect movement

Velocity: Measurement of speed as well as the direction. Velocity changes when direction changes even when speed stays the same.

Terminal velocity: When something falls through gas or liquid it accelerates at a decreasing rate until it reaches its maximum constat velocity. This is terminal velocity. Happens when force of gravity equals air resistance to its falling.

Friction: The resistance of one surface to slide over another. Friction is everywhere. Without it nothing would stop moving. Wheels lose less motion to friction because they don’t have to slide at any time. Oil reduces friction. Friction causes movement energy to be converted to heat energy. The movement energy isn’t loss, it’s transferred!

Equilibrium: When forces or energies or systems are in balance

Inertia: The property of a stationary object to remain stationary and a moving object to remain moving unless acted upon by another force. (Including friction and gravity.)

Freefall: Any motion of anything where gravity is the only “force” (source of movement) affecting it. Objects in freefall are weightless because nothing is pulling it toward itself. (This is also why the weight of objects are different on different planets: there is a different amount of gravity working on the object.)

Weightlessness: Freefall, but not quite, because the object is inside of something, such as a spacecraft

Centripetal force: The “force” that causes something turn in a circle instead of in a straight line. It is not actually a force, but the net result of all the forces acting on the object that result in the circular movement.

Cohesion: When molecules of one substance are more attracted to each other than to the substance they’re touching. Ex: surface tension.

Adhesion: Opposite: Molecules are more attracted to substance they’re touching than to each other – ex: glue. Occurs often with liquids.

Diffusion: Molecules spread out to fill a space more evenly. Occurs often in gases.

Surface tension: Sideways and downward attraction on a liquid’s surface. Happens because molecules in water at top are more attracted to molecules in water below than to molecules in the air.

Fluid dynamics:

Turbulence: The uneven movement caused when an object moves through air or water

Drag/air resistance: Friction that occurs between air and any object moving through it. 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. Compressed air is an especially highly pressurized type of air.

Vacuum: An area of decreased air pressure that causes areas of higher air pressure to be drawn in towards it. When we suck or otherwise remove air from a container, we create a vacuum in that container. That vacuum, in turn, sucks air into it. Note that it isn’t the motion of pulling out air that causes a vacuum cleaner to suck, but the natural physical reaction of higher-pressure air to rush to fill (and thus balance out) lower-pressure air that causes this behavior.

Outer space has no air, so it is considered a vacuum. If a person went to space without a spacesuit, they would explode immediately as all of the air in their body pushed outward toward the vacuum at once. Spacesuits provide air pressure to prevent this.

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.” Example: 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 term denoting the entire force of electricity and magnetism, both of which occur between electrically charged particles. This force is commonly shown as a spectrum, with visible light in the center, which is known as the electromagnetic spectrum.

Electromagnetic wave: Air waves made of continually changing electric and magnetic fields that can move through solids, liquids, gases and even a vacuum.

Electromagnetic spectrum/radiant energy: All parts of the electromagnetic spectrum, whether or not they are visible to the human eye, including (in order): gamma rays, X-rays, ultraviolet rays, visible light, infrared rays, radar, FM, TV, shortwave and AM.

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

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

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

Magnetic field: All the (invisible) space around a magnet that attracts iron. The field is strongest at the poles. The Earth is a large magnet, and has a magnetic field with two poles. It is strong enough that magnets will reorient to be parallel to the field, which is why compasses work.

The five properties of magnets: They only act on iron and iron-containing materials; 2. They have two ends, or poles (north-seeking and south-seeking); 3.They have a magnetic field; 4. Opposite pole attract, like poles repel (though both ends are attracted to iron); 5. Their magnetic fields pass through the other materials.

Magnetic north/south: The magnetic poles of the earth, which is a huge magnet. (These poles are slightly different from the geographical North Pole and South Pole.)

Ferromagnetism: The magnetic quality of certain materials (such as iron) that allows them 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 parts of the spectrum that are visible to the human eye/mind connection. Visible light is a very small part of the light spectrum.

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.)

Luminous: The giving off of light (as opposed to the mere reflecting of light) by an object

Light intensity: The measurable amount of light (or another property) present

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 parts of light rays that become visible when light reflects off an object. The human eye can’t see the light rays that gets absorbed by the same object. Since every object absorbs light differently, objects reflect light differently, too.

Fluorescence: The property of some substances that cause them to glow when exposed to light. This occurs because the material is able to absorb high-frequency wavelengths, like UV light, which is invisible to the human eye, but then emit visible light from that absorbed light. UV light works best to create the glow effect because it is a high-energy frequency. Note that some energy is lost in the energy conversion process, so high-energy frequency is needed so there’s enough energy left after conversion to cause the glow.

Phosphorescence: The property of some substances that cause them to glow. Unlike a fluorescent material, though, a phosphorescent material doesn’t immediately re-emit the radiation it absorbs; instead, it can re-emit it up to several hours after the absorption. Examples include glow-in-the-dark paint or toys. The reason for this ability to hold the energy has to do with quantum mechanics.

Dispersion: For example, at sunrise and sunset light has to travel through more of the atmosphere before reaching your eyes. Blue is scattered before you see it, leaving lower frequency red and orange.

Prism: An object, such as a diamond or a piece of cut glass, that bends the white light that hits it, thereby splitting it and causing a rainbow to appear

Convex lens: A lens that is shaped like an upside-down bowl

Concave lens: A lens that is shaped like a bowl

Mirror: A piece of glass with a silver-painted backing behind it that causes all light to reflect back to the viewer

Converging lens: A lens that converges rays of light that are traveling parallel to its principle axis. This kind of lens corrects farsightedness.

Diverging lens: A lens that diverges rays of light that are traveling parallel to its principle axis. This kind of lens corrects nearsightedness.

Reflection: The bouncing of waves off a surface and back the opposite direction

Refraction: The change in path of a wave. We see light waves change path when we put a straw in a glass of water. The straw appears bended due to the changing of the path of light when traveling through air to traveling through water and vice versa.

Interference: The changing of a wave’s path resulting from an outside force

Diffraction: The splitting of light waves into two or more separate light waves when passing through small openings or encountering an obstacle

Constructive interference: The increase in a wave’s size due to interference

Destructive interference: The decrease in a wave’s size due to interference

Three types of heat transfer: Convection, conduction and radiation

Convection: Heat transfer through moving gases or liquids, such as ocean currents or warm air currents

Conduction: Heat transfer through solids using direct contact, such as a pan on a burner

Radiation: Heat transfer through the air or through space, such as the sun heating the atmosphere or a radiator heater heating a home’s air. The air does not have to be moving to transfer the heat energy.

Sound: The vibration that occurs in a hearing ear after sound waves contact it. Sound waves are only sound if they find a hearing ear. The sound waves bump the particles in the air and transfer the movement energy from particle to particle till it gets to the ear. (Note: Sound waves transfer movement energy while light waves travel as electromagnetic radiation. Sound will only travel through gas, liquid or solid, but not through a vacuum – no particles are there to transfer the energy. Light does, though, and thus it moves much faster than sound – 186,000mps rather than .2mps.)

Sound vibrationv/sound wave: Fast back and forth movements (waves) that produce sound

Sound wave: The wave pattern of sound vibrations

Tone: Any prolonged sound note

Pitch: A specific sound note (A, B-flat, etc.). 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

Frequency: The speed of a sound’s vibration. High frequencies =fast, low f=slow.
More tension = faster vibration = higher frequency = higher pitch.

Amplitude: Distance traveled from one side to another of the sound wae. More distance = louder sound.

How sound is made from voices: By passing air through the larynx and at the same time putting tension on the vocal cords. (To feel the vibration, touch the throat while talking.) Note that the human ear can only pick up 20 to 20,000 vibrations-per-second frequencies.

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 speed:

Subsonic speed:

Sonic boom: The sudden crashing sound that results when a noise breaks the sound barrier

Sound barrier:

Echo: Result of sound waves bumping hard surfaces and changing directions. Telephones change sound vibrations into electric signals. Same with cell phones, etc. Changed back to sound waves at the listener’s end.

Sonar: A way of bouncing ultrasound waves off far-away objects to determine their location

Theoretical physics:

The theory of everything: A theory that has not yet been found that explains how all of the different theories and laws (such as the law of gravity and quantum physics ideas) can work together in the same universe, even though they seem to contradict each other. The main two theories of everything are general relativity and quantum field theory. General relativity is the theory that all events are caused by gravity, while quantum theory discusses the interplay of the strong force (subatomic particles), the weak force (gravity) and the electromagnetic force. These theories are separately confirmed, but seem to contradict; it seems that even though they are both correct, they cannot both be correct. Since general relativity is used for large-scale problems and quantum theory is used for small-scale problems, their incompatibility is usually avoided.

String theory: The current favorite theory of everything since it attempts to marry general relativity and quantum theory by proposing that the four fundamental forces were, at the time of the Big Bang, a single force, and every particle in the universe is, at the smallest level, a pattern of vibrating strings with its own vibration pattern.


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