Conservation of energy

Energy is all around us.

It can change its shape. It does not go away. It just moves to new things.

Energy can turn into heat or sound. For example, an explosion makes a loud noise. It also makes heat. The energy just changes form. It does not vanish.

One person thought energy was like water. Another thought it was made of tiny bits. They wanted to know what things are made of. They were looking for the truth.

Energy can also move from one thing to another. It can move from a moving object to heat. This happens when things rub together. We call this friction.

It is a rule of our world. You cannot make new energy from nothing. You also cannot make it disappear. Energy is always here in some way.

Energy is a special part of our world. It follows a very important rule. This rule says energy cannot be made or destroyed.

Instead, energy can only change its form. It can also move from one thing to another. For example, an explosion uses chemical energy. That energy turns into heat, sound, and movement.

Many thinkers studied this over a long time. A scientist named Émilie du Châtelet did great work. She used balls and soft clay to study energy. She showed how energy from a falling ball moves into the clay.

Later, people learned that motion can turn into heat. This happens when things rub together. This is called friction.

Scientists also found that mass and energy are linked. Mass is the amount of matter in an object. In extreme places, mass can turn into energy. This happens in things like black holes.

Because of this rule, a machine cannot run forever on its own. It always needs a way to get new energy.

Energy is a special part of our world. It follows a very important rule called the law of conservation of energy. This law says that energy cannot be created or destroyed. Instead, it can only change from one form to another. It can also move from one thing to another.

This means the total amount of energy stays the same. In a closed system, energy only changes if it enters or leaves. For example, an explosion uses chemical energy. That energy turns into heat, sound, and movement. If you add all those parts up, they equal the starting energy.

Scientists have found that mass and energy are actually linked. This is shown by a famous equation in special relativity. This means mass can turn into energy and vice versa.

We see this happening in the tiny centers of atoms. This is called nuclear binding energy. It is also important in very extreme places in space. This includes the universe right after the Big Bang. It also happens when black holes emit something called Hawking radiation. Because of this rule, a machine cannot run forever on its own. A machine that works without any new energy is called a perpetual motion machine of the first kind. These machines cannot exist.

Many thinkers studied these ideas over a long time. Ancient philosophers like Thales of Miletus had ideas about this in 550 BCE. Empedocles wrote about this around 490 to 430 BCE. He believed things just rearranged themselves. Epicurus also had ideas about this in 350 BCE. He thought the total amount of things stayed the same.

Later, Simon Stevin solved math problems using this idea in 1605. Galileo published his own work in 1639. He studied how things move and fall. He showed that a moving object rises to the same height it fell from. This helped people understand how energy moves back and forth.

Different scientists added more pieces to the puzzle. Christiaan Huygens studied how objects hit each other in 1669. He noticed that kinetic energy stayed the same in some hits. Gottfried Leibniz worked on this between 1676 and 1689. He called this moving energy "vis viva," or living force.

Daniel Bernoulli also studied this in his 1738 book. He looked at how water flows and how gas works. Émilie du Châtelet did very important tests too. She dropped balls into soft clay to see how they moved. Her work helped show that energy has a specific math rule. This helped people see that energy is different from momentum.

In the 1800s, people learned how motion turns into heat. This often happens because of friction.

Scientists like Gaspard-Gustave Coriolis used these ideas for engineering. They called it "mechanical work." Karl Friedrich Mohr wrote about this in 1837. He said energy could look like light, electricity, or magnetism. It can transform from any one form to another. This is why we can use many different tools today. We use energy to make light, heat our homes, and move cars. It is the invisible force that keeps the world working.

The law of conservation of energy is a fundamental principle of physics. It states that the total energy of an isolated system remains constant over time. In a closed system, the total amount of energy can only change if energy enters or leaves that system. A key part of this law is that energy can neither be created nor destroyed. Instead, energy is only transformed from one form to another or transferred between objects.

This principle explains why the universe operates in a predictable, balanced way.

To understand how this works, we can look at a chemical reaction, such as an explosion. When dynamite explodes, its stored chemical energy is converted into other forms. These forms include kinetic energy, which is the energy of motion, and potential energy in the flying pieces. The explosion also releases energy as heat and sound. If you add up all these different forms of energy, the total will exactly equal the amount of chemical energy that was lost during the combustion. This shows how energy moves through a process without ever disappearing.

Modern science has expanded this idea through special relativity. While classical physics treated mass and energy as separate things, special relativity shows they are related. The equation for mass-energy equivalence demonstrates that mass can be converted into energy and vice versa.

We observe this in the nuclear binding energy found in atomic nuclei, where a mass defect occurs. This relationship becomes very important in extreme environments. Examples include the universe shortly after the Big Bang or when black holes emit Hawking radiation.

Historically, humans have wondered about the permanence of the world for thousands of years. Around 550 BCE, Thales of Miletus suggested an underlying substance made everything. Empedocles, writing between 490 and 430 BCE, argued that the four elements—earth, air, water, and fire—only undergo continual rearrangement.

In 350 BCE, Epicurus believed the universe was made of indivisible units of matter. He stated that the sum total of things would always remain as it is now. These early ideas were precursors to our modern understanding of conservation.

Scientific progress accelerated during the 17th century. In 1639, Galileo analyzed the motion of pendulums. He observed that a moving body rises to the same height from which it fell. This showed how energy converts between potential and kinetic forms. In 1669, Christiaan Huygens studied collisions and noted that kinetic energy was invariant in certain cases.

Later, between 1676 and 1689, Gottfried Leibniz developed the concept of "vis viva," or living force. He used this to describe the energy associated with motion in mechanical systems.

In the 18th century, Émilie du Châtelet provided crucial evidence for these theories. She tested how kinetic energy relates to velocity by dropping balls into soft clay. Her experiments showed that the deformation of the clay was proportional to the height of the drop.

This helped prove that energy was distinct from momentum. Daniel Bernoulli also contributed significantly in 1738. He linked the kinetic energy of gas molecules to temperature and studied how energy behaves in flowing water. These studies helped move science toward understanding how energy is conserved in fluids and gases.

By the 19th century, scientists began to understand the connection between motion and heat. For a long time, people believed in the caloric theory, which said heat was a substance that could not be destroyed. However, observations showed that mechanical motion could be converted into heat through friction.

This led to the concept of the mechanical equivalent of heat. Engineers like Gaspard-Gustave Coriolis and Jean-Victor Poncelet began using "mechanical work" in their calculations. They helped bridge the gap between abstract physics and practical engineering. Today, we recognize that energy can transform into light, electricity, magnetism, and many other forms.