Energy

Energy makes things work.

It can be heat or light. It can also make things move. Energy cannot be made or lost. It only changes form.

The sun sends energy to Earth. This helps the whole world. Plants catch sunlight to make food. Animals then use that food. All living things need energy to grow. Energy is everywhere in our world.

Energy is what makes things work. It can show up as heat or light. It can also make things move.

There is a special rule for energy. It is called the law of conservation of energy. This law says energy cannot be made or lost. It can only change from one form to another. Scientists measure energy in a unit called a joule.

Energy has many different forms. Kinetic energy is the power of a moving object. Potential energy is energy that is stored. For example, an object might store energy based on its position. There is also chemical energy. This is found in chemical reactions.

Living things need energy to grow and function. Plants catch radiant energy from the Sun. They use sunlight to make food through photosynthesis. Animals get energy from the food they eat. This energy helps all living things stay alive. The Sun also drives the weather and life on Earth.

Energy is a special property that makes things happen. It is what allows a body to do work. You can see energy when it appears as heat or light.

One very important rule is the law of conservation of energy. This law says that energy cannot be created or destroyed. It can only change from one form to another. Scientists use a unit called the joule to measure it.

Energy can be split into different types. Kinetic energy is the energy of a moving object. Potential energy is energy that is stored, often because of an object's position. There is also chemical energy found in chemical reactions. Radiant energy travels through light and electromagnetic radiation. Some energy is even stored inside the tiny parts of an atom. These different types often work together in one system.

People have studied energy for a very long time. The word comes from the Greek word "energeia."

This word might have first appeared in the work of Aristotle. In the late 1600s, Gottfried Leibniz spoke of a "living force." Later, Émilie du Châtelet helped describe how energy is conserved. In 1807, Thomas Young began using the word "energy" in a modern way.

Many scientists added to our knowledge with specific discoveries. James Prescott Joule found a link between work and heat in 1845.

In 1905, Albert Einstein showed that mass can turn into energy. This was part of his theory of special relativity. Later, Niels Bohr proposed ideas about energy levels in atoms in 1913.

These discoveries helped us understand how the whole universe works.

Energy is part of everything you see every day. Living things must take in energy to grow and stay healthy.

Plants catch radiant energy from the Sun to make food. This process is called photosynthesis. Animals get their energy by eating nutrients like proteins or sugars. Even the weather on Earth is driven by energy from the Sun.

Everything in nature relies on this constant flow of energy.

Energy is a fundamental property of the physical world. It is a quantitative property transferred to a body or a physical system. This transfer is recognizable through the capacity to do work. Energy also manifests in forms such as heat and light.

A vital rule in physics is the law of conservation of energy. This law states that energy cannot be created or destroyed. Instead, energy can only be converted from one form to another. Scientists measure energy using the joule (J) in the International System of Units.

Scientists classify energy into several distinct categories. The total energy of a system can be divided into kinetic and potential energy. Kinetic energy is determined by the movement of an object. This includes the composite motion of all its components. Potential energy reflects the potential for an object to have motion. This is often based on an object's position within a field. Some systems combine these into mechanical energy. This is the sum of translational and rotational kinetic and potential energy. Other specific forms include chemical energy and radiant energy. Radiant energy is carried by electromagnetic radiation. There is also rest energy associated with an object's rest mass.

Different scientific fields study energy in unique ways. In classical mechanics, energy is a useful conserved quantity. Work is a function of energy defined as force times distance.

In chemistry, energy is an attribute of a substance's structure. Chemical transformations involve changes in atomic or molecular structures. These changes are usually accompanied by changes in total energy. An exothermic reaction occurs when the final state has lower energy than the initial state. In contrast, an endothermic reaction is the reverse. Reactions often require activation energy to overcome an energy barrier.

Biology relies entirely on the constant flow of energy. All living organisms must take in and release energy to function. This enables growth, development, and the functioning of cells. The Earth's ecosystems are driven by radiant energy from the Sun. Green plants capture this sunlight through photosynthesis. They convert carbon dioxide and water into carbohydrates and oxygen. This process turns radiant energy into chemical potential energy. Animals obtain energy by consuming nutrients like lipids and proteins. These nutrients are used in cellular respiration to release energy.

Our understanding of energy has evolved through history. The word comes from the Ancient Greek word "energeia," meaning activity. Aristotle used this term in the 4th century BC. However, his version was a qualitative philosophical concept. In the late 17th century, Gottfried Leibniz proposed "vis viva," or living force. He believed total living force was conserved.

Émilie du Châtelet later proposed the concept of conservation of energy. Her work helped define a measurable quantity distinct from momentum. In 1807, Thomas Young began using the modern term "energy."

Many researchers contributed to the formalization of energy laws. James Prescott Joule discovered the link between mechanical work and heat in 1845. This helped lead to thermodynamics, formalized by William Thomson. Rudolf Clausius and others used thermodynamics to explain chemical processes. In 1905, Albert Einstein changed everything with special relativity. He showed that rest mass corresponds to rest energy. This means mass can be converted into forms like kinetic or radiant energy. This discovery merged the laws of mass conservation and energy conservation.

Modern physics has explored energy at the smallest scales. Joseph von Fraunhofer and William Hyde Wollaston observed spectral lines in the 1800s. This provided the first evidence of energy quantization in atoms. In 1913, Niels Bohr proposed quantized energy levels in his atomic theory. Later, Erwin Schrödinger and Werner Heisenberg advanced quantum mechanics. They explained these levels using the Schrödinger equation. Today, we know that energy conservation is linked to the laws of physics not changing over time. This deep connection is described by Noether's theorem.