Transmission in science refers to the transfer of energy, matter, or information from one place to another. It’s a broad concept that shows up across nearly every branch of science, from the light passing through a window to a virus spreading between people to electricity traveling hundreds of miles through power lines. The core idea is always the same: something moves from a source to a destination, and the medium it travels through shapes how efficiently that transfer happens.
Transmission of Light and Waves
In physics, transmission most often describes what happens when light or another wave passes through a material. When sunlight hits a pane of glass, some of that light reflects off the surface, some gets absorbed by the glass itself, and the rest passes through to the other side. That last portion is the transmitted light. Scientists quantify this with a value called transmittance: the ratio of light that makes it through a material compared to the light that hit it. Transmittance ranges from 0 (nothing gets through) to 1 (everything gets through).
There’s a simple rule that governs any material light strikes: the fractions that are reflected, absorbed, and transmitted must add up to 1. If a material absorbs 30% of the light and reflects 10%, then 60% is transmitted. This relationship is why materials fall into three familiar categories. Transparent materials like clear glass transmit most light. Translucent materials like frosted glass transmit some but scatter it, so you can’t see a clear image. Opaque materials like wood or metal transmit essentially none.
Sound Transmission Through Different Materials
Sound also transmits through materials, but the rules are different from light. Sound is a pressure wave, and it needs a medium to travel through. It can’t move through a vacuum at all. Two properties of a material determine how fast sound moves through it: how rigid it is and how dense it is. Greater rigidity speeds sound up, while greater density slows it down.
In practice, solids are both denser and far more rigid than gases, and rigidity wins out. Sound travels through air at about 331 meters per second, through fresh water at roughly 1,480 meters per second, and through steel at about 5,960 meters per second. That’s why you can hear a train coming by pressing your ear to the rail long before the sound reaches you through the air. Temperature also matters, especially in gases, because it affects density. Warmer air transmits sound slightly faster than cold air.
Heat Transmission
Heat moves from warmer objects to cooler ones through three distinct mechanisms: conduction, convection, and radiation.
Conduction is heat traveling through a solid material by direct contact. When you touch a hot pan, heat conducts from the metal into your hand. On a hot day, heat conducts through your home’s roof, walls, and windows. Insulation works by slowing this process down, using materials that are poor conductors.
Convection transfers heat through the movement of fluids, meaning liquids or gases. Hot air rises, carrying thermal energy upward and creating circulation patterns. This is why the upper floors of a building tend to be warmer, and it’s the principle behind both natural breezes and forced-air heating systems.
Radiation transmits heat as electromagnetic waves, including visible light and infrared radiation. You don’t need any physical medium for this. It’s how the sun warms the Earth across 93 million miles of vacuum, and it’s why you can feel the heat from a stove burner even from across the room. The infrared radiation carries energy directly from the hot object to your skin without heating the air in between.
Electrical Transmission
When scientists and engineers talk about electrical transmission, they mean moving electricity from power plants to the homes and businesses that use it. This happens through networks of high-voltage power lines that can stretch hundreds of miles. Some energy is inevitably lost as heat along the way, mainly because the wires themselves have electrical resistance.
The U.S. power grid has gotten remarkably efficient at this. Over a 70-year span, transmission and distribution losses dropped from about 15% to below 5% as of 2022. The biggest improvement came from raising the voltage of transmission lines. Higher voltage allows the same amount of power to be carried with less current, and lower current means less energy wasted as heat in the wires. More recently, smart grid technologies that monitor and manage electricity flow in real time have further reduced inefficiencies.
Data and Signal Transmission
In communications and computer science, transmission refers to sending information from one point to another. The medium carrying that information can be physical or wireless. The three main types of physical media are twisted pair wire (the copper wiring in telephone lines), coaxial cable (which carries TV signals and internet with minimal distortion), and fiber optic cable (which transmits data as pulses of laser light and offers the highest speeds).
Wireless transmission sends information through the air using electromagnetic waves. Broadcast radio distributes signals over long distances between cities or countries. Microwaves provide high-speed transmission and are commonly used for satellite communication and cellular networks. In every case, the same basic principle applies: a signal is generated at one end, travels through a medium, and is received at the other.
Disease Transmission in Biology
In biology and medicine, transmission describes how infectious agents spread from one host to another. This is the meaning most people encountered during the COVID-19 pandemic. There are two broad categories: direct and indirect transmission.
Direct transmission happens when an infectious agent moves straight from one person to another. This includes physical contact, such as skin-to-skin touching, and droplet spread, where coughing, sneezing, or talking projects pathogen-containing droplets. These droplets are too large and heavy to stay airborne for long, so they typically travel only short distances before falling.
Indirect transmission involves an intermediary. Airborne transmission occurs when tiny particles (smaller than five microns) remain suspended in the air for extended periods and can travel long distances while still being infectious. Vector-borne transmission relies on another organism, often an insect like a mosquito or tick, that carries the pathogen. In biological vector transmission, the pathogen actually multiplies or develops inside the vector before it can infect a human host.
Scientists measure how transmissible a disease is using a metric called R0, pronounced “R naught.” It represents the average number of new infections one sick person will cause in a population where everyone is susceptible. If R0 is greater than 1, the outbreak is expected to grow. If it’s below 1, the outbreak will fade. R0 also helps public health officials estimate what fraction of a population needs to be vaccinated to stop a disease from spreading.
Genetic Transmission
Genetic transmission is the process by which traits pass from parents to offspring through DNA. Each gene can exist in different versions, called alleles, and a child inherits one allele from each parent. How those alleles interact determines which traits appear.
A dominant allele produces its effect even when only one copy is present. A recessive allele only shows up when a person inherits two copies, one from each parent. This is why two brown-eyed parents can have a blue-eyed child: both parents can silently carry one recessive allele for blue eyes without showing the trait themselves. There are five basic inheritance patterns for single-gene traits: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, and mitochondrial. In autosomal dominant conditions, an affected person typically has an affected parent and the trait appears in every generation. In autosomal recessive conditions, both parents are usually unaffected carriers, and the trait can skip generations entirely.
Mechanical Transmission
In engineering, transmission refers to transferring mechanical power from one component to another, usually while changing speed or force along the way. The transmission in a car is the most familiar example: it connects the engine to the wheels and allows the driver (or an automatic system) to shift between gear ratios for different driving conditions.
The main components used in mechanical transmission systems are gears, belts, and chains. Gears mesh directly together and are the most precise option, available in several configurations including spur gears for parallel shafts, bevel gears for shafts at 90-degree angles, and worm gear sets for high reduction ratios. Belts and pulleys are used when shafts are too far apart for gears to mesh directly. Chains handle situations where the distance is too great for gears but the forces involved are too high for belts. Couplings connect two shaft ends directly when no speed change is needed.
The Common Thread
Across every branch of science, transmission comes down to the same idea: something travels from point A to point B, and the path it takes determines how much arrives and in what condition. Whether you’re measuring the percentage of light that passes through glass, the fraction of electricity lost over power lines, or the number of people one sick person infects, you’re always asking the same fundamental question: how effectively does this transfer happen?