What is energy?
Actually, physics has not yet fully explained its “true nature.”
However, one thing is certain: energy never disappears; it only continues to change its form.
In this episode, we will explain the law of conservation of energy as a simple story, incorporating the analogy of “building blocks” introduced by Feynman. Please enjoy this grand journey of energy, connecting from the sun to our very lives.
You may have woken up today, walked, eaten, worked, or studied. You might have charged your smartphone, boiled water, or watched a car drive by.
These seemingly unrelated events have one thing in common.
It is that they are all working while energy changes its form.
However, I have one question.
What exactly is energy?
“Is it force?”
“Is it electricity?”
“Is it vitality?”
While the word is used in various ways in daily life, energy in physics is a little different.
Richard Feynman gives a very impressive explanation of energy near the beginning of “The Feynman Lectures on Physics.” He said this:
“It is important to realize that in physics today, we have no knowledge of what energy is.”
You might find this surprising. Even physicists do not explain the “true nature of energy.”
Then, what do we know?
It is that energy has a surprising property.
That is the property that it never disappears. It may change its form.
However, looking at the universe as a whole, its total amount does not change.
This is called the law of conservation of energy.
Feynman explained this concept using the analogy of a child’s building blocks.
Suppose a child has 28 building blocks.
If you count them every day, there are always 28.
One day, when you count them, there are only 26.
“Two are gone!” you think.
However, when you look under the bed, you find two. There are 28 again.
The next day, there are only 24.
This time, you open the toy box and find four inside. There are 28 in total again.
Even if the blocks are out of sight, they haven’t disappeared anywhere.
They have just changed their location.
Feynman said that energy is just like this.
We cannot see it. However, it is just changing into various forms.
For example, a stone in a high place. This stone has energy before it falls. This is called potential energy.
When you drop the stone, that potential energy gradually changes into kinetic energy. The stone falls faster and faster. And when it hits the ground, it makes a “thud” sound. A little heat is also generated.
The stone is slightly deformed, and the ground is also slightly deformed.
In other words, the kinetic energy has changed into sound and heat.
It has not disappeared. It has only changed its form.
We are the same. We eat breakfast. Food stores chemical energy. That changes into kinetic energy in our bodies. We can walk. We can exercise. It also changes into heat energy to maintain body temperature. We also use energy to think. If energy is not supplied, humans cannot live.
Cars are the same. Gasoline has chemical energy.
It becomes heat by burning inside the engine.
That heat moves the pistons, turns the wheels, and the car moves forward.
In the end, it changes into heat through the brakes.
It has not disappeared either. It is just changing its form.
The sun is also a huge energy factory.
In the center of the sun, hydrogen undergoes nuclear fusion, releasing enormous energy. That light takes about 8 minutes to reach Earth.
Plants use that light to perform photosynthesis. Animals eat plants.
We also receive that energy through our meals.
In other words, the energy that is moving your body right now was originally born inside the sun. What a grand story.
Feynman believed that knowing such connections in nature is the joy of physics. Phenomena that seem unrelated at first glance are actually connected by a single thread. That is where the beauty of science lies.
However, there is still a great mystery about energy.
We know that energy is conserved.
We can also calculate energy.
But there is still no complete answer to the question, “What is energy?”
Feynman did not try to hide that fact.
Admitting that you don’t know what you don’t know.
That is where new science begins.
Today, we learned about one of the most mysterious existences in the universe: energy. It continues to circulate through the universe without disappearing, while changing its form.
Our lives, the sunlight, the flowing rivers, and the blowing wind.
Everything is a scene in the grand story called energy.
Next time, “What is heat?” Let’s continue our journey into the surprising world of molecules hidden behind the familiar sensations of hot and cold.
※ This series is a story based on the concepts of “The Feynman Lectures on Physics.” A total of 58 episodes are planned.
Please enjoy it with me until the end.
Next episode is here
Previous episode is here
Episode 1 is here
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Introduction to Kou-ji World
Director: Kou-ji
Story and Prompt: ChatGPT
Images and Video: Flow (Nano Banana 2)
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