Sunlight contains many colors. When it enters Earth’s atmosphere, small gas molecules scatter shorter blue wavelengths more strongly than longer red wavelengths. What sunlight contains Visible sunlight is a mixture of colors with different wavelengths. Red light has a longer wavelength, while blue and violet light have shorter wavelengths. Human vision is more sensitive to…

Water continually moves through evaporation, condensation, precipitation, infiltration, and runoff. Energy from the Sun drives much of this circulation. Evaporation and transpiration Heat changes liquid water in oceans, lakes, rivers, and soil into vapor. Plants also release water vapor through a process called transpiration. Together, these processes move moisture from Earth’s surface into the atmosphere….

A blockchain is a shared digital ledger that records transactions in linked groups called blocks. Copies of the ledger can be maintained across a network of computers. How a blockchain is organized Transactions are collected into blocks. Each block generally includes a reference to the previous block, creating a chronological chain. Cryptographic techniques make unauthorized…

Vaccines train the immune system to recognize a specific pathogen or part of it. This preparation can help the body respond more quickly if it encounters the pathogen later. How immune training works The immune system identifies foreign features called antigens. A vaccine presents an antigen, or instructions for making one, in a way designed…

DNA is a molecule that stores biological instructions. Its sequence of chemical bases helps cells build proteins and regulate many life processes. What DNA is DNA is organized into long molecules made from smaller units called nucleotides. Four chemical bases form the information system of DNA, and the order of those bases carries biological instructions….

Robotics combines mechanical engineering, electronics, software, sensing, and control systems to build machines that act in the physical world. How robots operate Sensors collect information about the robot and its surroundings. Software interprets that information, and actuators create movement. Controllers coordinate these parts so a robot can perform tasks with an appropriate level of precision…

Quantum computers use quantum bits, or qubits, whose states are managed according to quantum mechanics. Unlike ordinary bits, which represent either zero or one, qubits can be prepared in combinations of states and manipulated with quantum operations. What makes them different Superposition allows a quantum system to represent several possible states in a calculation, while…

GPS receivers estimate location by comparing timing signals from multiple satellites. Because radio signals travel at a known speed, the time taken to arrive helps the receiver calculate the distance to each satellite. From signals to position A receiver uses signals from several satellites to calculate latitude, longitude, and altitude. It also corrects for timing…

Renewable energy comes from sources that naturally replenish, including sunlight, wind, moving water, and geothermal heat. These resources can provide electricity and heat without relying exclusively on finite fossil fuels. Major sources Solar panels convert sunlight into electricity, while solar-thermal systems use the sun’s heat. Wind turbines use moving air, hydropower uses flowing water, and…

Batteries store energy chemically and release it as electricity when needed. They power phones, laptops, vehicles, medical devices, tools, renewable-energy systems, and emergency backup equipment. How batteries work A battery contains electrodes and an electrolyte that allow chemical reactions to move electrons through an external circuit. When the battery is charged, electrical energy reverses the…