Energy facts for kids
Quick facts for kids Energy |
|
|---|---|
|
|
|
Common symbols
|
E |
| SI unit | joule (J) |
|
Other units
|
kWh, BTU, calorie, eV, erg, foot-pound |
| In SI base units | J = kg⋅m2⋅s−2 |
| Extensive? | yes |
| Conserved? | yes |
| Dimension | M L2 T−2 |
Energy is the ability to do work, cause movement, or make change happen. It powers everything in our world, from a speeding rocket to a glowing campfire. Whenever an object moves, warms up, or creates light, energy is involved. In the International System of Units, scientists measure energy in units called the joule (J).
All living things need energy to grow, run, and survive. Our planet's weather, winds, and living systems are powered by radiant energy that travels across space from the Sun. Energy cannot appear from nowhere, and it cannot vanish. It can only be transformed from one form into another.
Contents
What Are the Different Forms of Energy?
Scientists group all energy into two main types: energy that is stored, and energy that is moving. Stored energy is called potential energy. When an object begins to move, that stored power turns into kinetic energy. Many familiar forms of energy are combinations of these two types.
Moving Energy
Kinetic energy is the energy of moving things. A flying baseball, a racing bicycle, and a spinning wheel all have kinetic energy. When an object spins, scientists call that movement rotational energy.
Tiny particles inside matter are also constantly buzzing around. The motion of these microscopic particles creates thermal energy, which we feel as heat. When energy travels through matter in ripples that make our ears vibrate, we call it a sound wave or sound energy.
Stored Energy
Potential energy is waiting to be set free. When you stretch a rubber band, it holds elastic energy. The band wants to snap back to its original shape.
When you lift an object off the ground, it gains gravitational energy. If you let it go, the Earth's gravity pulls it downward, turning that stored power back into fast motion. Huge reservoirs behind a hydroelectric dam store water this way to generate electric energy.
Hidden Energy in Matter
Matter holds great amounts of invisible energy locked inside its tiny building blocks. Chemical energy is stored inside the bonds that hold molecules together. It is found in the food we eat, in wooden logs, and inside an electric battery. When we burn wood, chemical bonds break and release light and thermal energy.
Even deeper inside matter, atoms have their own stored power. Ionization energy holds an electron to its atom. Deep in the middle of each atom sits the atomic nucleus. The tiny particles called nucleons, which are made of even smaller bits called quarks, are bound tightly together by nuclear binding energy. Releasing this power produces nuclear energy.
How Energy Changes and Transforms
Energy changes its costume all the time! A device that switches energy from one form to another is called a transducer. For example, a heat engine changes heat into mechanical work.
A playground pendulum swings back and forth in an endless dance of energy change. At the top of its swing, it stops moving for a split second. At that moment, its kinetic energy drops to zero and its gravitational potential energy reaches its maximum. As it swoops downward, the potential energy changes into fast kinetic energy.
The Law of Conservation of Energy
The law of conservation of energy is one of the most important rules in all of physics. It states that within an isolated system, energy cannot be created or destroyed. The total amount of energy at the beginning must equal the total amount at the end.
Famous physicist Richard Feynman once explained that energy is like a collection of blocks that never change in number. You can move the blocks around, hide them in a box, or change their colors, but when you count them up, the total number is always exactly the same. In 1918, mathematician Emmy Noether proved this through Noether's theorem, showing that this rule comes from the fact that natural laws do not change over time.
Energy and Mass Are Twins
In 1905, the famous scientist Albert Einstein discovered something amazing in his theory of special relativity. He proved that mass and energy are actually two sides of the same coin. He showed this relationship in his famous equation:
This equation explains that even an object sitting completely still has rest energy tied to its rest mass. Because the speed of light (c) is such a gigantic number, a tiny crumb of matter contains an enormous amount of energy.
Measuring Energy in Science
.png)
Scientists use mathematics to calculate energy with great care. In physics, work is done whenever an applied force moves an object over a distance.
One joule is the work done when a force of one newton pushes an object across a distance of one meter. When we talk about how fast energy is used, we measure power in units called the watt. One watt means using one joule of energy every second. When you leave a light bulb on, your home uses electricity measured in a kilowatt-hour.
Energy in Nature and Living Things
Without energy, life on Earth could not exist. Plants act like tiny green factories. In a process called photosynthesis, they take in sunlight's radiant energy and convert water and carbon dioxide into sugars. This stores energy as chemical bonds in plants, which form the base of our planet's food chain.
Energy in the Human Body
Humans and other animals eat plants and other foods to get the energy they need. The nutrients we eat include carbohydrates, lipids, and proteins. Inside our body's cells, microscopic structures called the mitochondrion turn these food fuels into a tiny molecule named adenosine triphosphate (ATP).
Scientists call ATP the "energy currency" of the cell. Whenever your heart beats, your lungs breathe, or your legs run, your cells spend ATP molecules. The minimum amount of energy your body needs just to stay alive while resting is called your basal metabolism rate.
Powering the Earth and the Stars
Deep inside the Earth, the radioactive decay of heavy elements like uranium creates underground heat. This intense thermal energy drives plate tectonics, lifting huge mountains and triggering earthquakes.
Far out in space, the universe is full of giant energy events. In our Sun, the nuclear fusion of hydrogen atoms creates the blinding light and warmth that shines down on our planet every day. Exploding stars called a supernova, mysterious black holes, and distant quasars are the most powerful energy powerhouses in the cosmos.
History of Energy Discoveries
The word energy comes from the ancient Greek word energeia, used by Aristotle long ago. In the late 1600s, thinker Gottfried Leibniz studied moving bodies and spoke of a living force called vis viva. In the 1700s, French scientist Émilie du Châtelet helped develop the idea of the conservation of energy by studying motion and speed.
In 1807, scientist Thomas Young became the first person to use the word "energy" in its modern scientific sense. Later, in 1845, James Prescott Joule showed that moving mechanical parts create heat in water, proving that motion and thermal energy are directly linked. Today, physicists continue to study energy at the tiniest levels using quantum mechanics, showing how atoms absorb and release energy packets called photons.
See also
In Spanish: Energía para niños
- Combustion
- Efficient energy use
- Power station
- Sustainable energy
