Every subject is interesting, but all classes are boring.

"I am just going to pretend that I don't know anything about work and energy, OK?" The janitor said when we met again today.

Not really a difficult job, I thought to myself.

"So, we know that energy is the ability to work. And work is..."

Both of us did not remember Wikipedia's definition of work. I was about to fire up the browser, but he stopped me.

"Let us just go with common sense definition of work, okay?" The janitor said. "What is work according to you?"

"If you lift or move something then I would say you have done work," I said.

"Great, I like it," The janitor said. "Let us go with that definition."

Then he took my notebook, tore a paper and balled it and kept on the table. If a classmate of mine had done it we would be rolling on the ground fighting. But he was twice my size and his dress was little dirty. So I let it slide.

"If something can move this ball, then it has energy according to your definition. Do you agree?" He asked me.

I nodded in agreement. "See! I can push it," I said gently tapping the paper ball. It rolled along the table towards him."So I have energy," I said.

"So do I," he said and tapped the ball back to me.

"Now we know that wind has energy, because...," I blew on the paper ball with my mouth and it bounced across to the janitor.

"Wind is flowing air, I get it. Great! So wind has energy," The janitor said as he took the ball and placed it back at the center.

"What other energy do you know?" The janitor asked.

"Magnetic energy," I said and immediately.

"Magnetic energy! Interesting. How can a magnet move a paper ball?"

Everybody knows magnet can't move a paper ball. Did that mean there is nothing called magnetic energy? Of course there is. Because magnets can move other magnets.

"Maybe we should not limit our test to just paper balls. We should include nails also," Janitor said. But we didn't like that idea because energy is energy right? It should be able to move everything.

Then an idea struck me. I came up with an ingenious way to move the paper ball with a magnet because I was smart and had a good knowledge of history! 

Maybe you already know how to do it. If not, spend a minute on the picture below and you would get a clue.

We say Shah Jahan built Taj Mahal. But he didn't, did he? 
He just got it built from some people who we don't even know.

The solution I came up with was simple.

"Let us keep a magnet near the paper. Now when we bring a second magnet near the first magnet, the two magnets will repel. The first magnet will move and strike the paper ball and move it," I said triumphantly.

"Bravo! The first magnet moves the second magnet and the second magnet moves the paper ball." He said exultant. "You must be the most intelligent student in your class."

I felt great, but just for a moment. Because the janitor came up with a bigger breakthrough next.

"Wait! The second magnet moved because of the magnetic energy of the first magnet. But what moved the paper ball? Definitely not magnetic energy?" The janitor asked.

He was right. If magnetic energy can move paper ball, there was no need for the second magnet. Magnetic energy is present between only magnets. But somehow I had used that magnetic energy to move a paper ball.

Maybe, I should get a Nobel prize!

"Actually what you did is not all that remarkable, isn't it?" The janitor asked as he tore another paper out of my notebook.

Man! He took away from me a Nobel prize and a paper. Just like that!

The janitor rolled the paper and made another ball and placed it near the first paper ball.

"Watch what I am doing," He said and tapped the first ball. It rolled and hit the second ball which moved.

"Isn't this exactly what you did, but with magnets?" The janitor asked.

I nodded and the janitor said, "You see, the second magnet did not move the paper ball because it was a magnet, but because it was moving. When an object is at rest, it has no energy and it can't move a paper ball. But when it moves, it has some energy because it can hit a paper ball and make it move. But what is that energy?"

"Kinetic energy!" I exclaimed. "Energy due to movement is called kinetic energy. I have studied about that."

"Wow! Kinetic energy, huh!" The janitor said impressed. "I didn't know it at all. You are awfully smart."

Okay, he figured it out himself, but I gave the correct name. Without me, he would have called it Tantric energy of movement or something like that.

"So I hit the ball and move it which means I did work...," the janitor was talking to himself, " and the ball started moving. And because of moving, it has kinetic energy. Since it has energy it can do work now. It can hit another ball and make that move."

I saw where he was coming from, but I didn't see where he was going.

"Oh my God! I understood what they said in Wikipedia. Work is nothing but transferring energy from one to another. By hitting the ball, I did some work. And that work transferred energy from me to the ball which started moving. Now it hits another ball and does work on it. When it does that, it transfers some kinetic energy from it to the other ball," He said.

"Yes! It is called conservation of energy," I said.

"What.." he asked puzzled, "conversation, did you say?"

"No! Conservation. It means energy is neither created nor destroyed. It is just transferred from one form to another; one part of system to another. You transferred the energy from inside you to the first ball. The first ball transferred it to the second ball"

"Wow! you know a lot of things," he said.

"No! I thought I knew. But I never could have explained before." I said. "But now I really know"

The janitor nodded and said, "You know what Feynman said, right? If you can't explain it to a six year old, then you don't know it."

"Who is Feynman?" I asked.

"I don't know," the janitor shrugged. "There are lot of books with his name in the shelf. But nobody issues it though."

We sat there trying to process what we had achieved. We had understood work and energy, and how work just transfers energy from one form to another. Sure, I have been studying it from class six. But today I understood! And for that, I had to thank the janitor, because without him, I don't think I could have understood.

"Thanks," I told him as we switched off the library lights and got ready to leave. "I think you must be the most intelligent janitor in the library."

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