It's all heating up!

I took the chalk and walked towards the board. I could have stood there doing nothing. But it would have just prolonged my agony. I had had enough of it. I was just going to tell something, let the teacher have some fun, and then go back to desk and become Mr. Invisible for the rest of the year.

'Work and Energy,' I wrote on the board.

"Work is pushing or lifting something. We need energy to do work," I started mechanically.

"Sir! I have a doubt," a voice came. It was the class teacher. He had his hands raised.

There was suppressed giggle in the class room.

"You say we need energy to do work, right?" The teacher said.

I nodded.

"Okay, Let us say I don't do any work. I just sleep or I hibernate like a bear." He stretched his hands out sideways and made a guttural sound - Grrrrr! Grrrrr! - a poor imitation of a bear. But the class laughed.

"Do I still need energy? Do I still need to eat food?"

I smiled inside. This was the first doubt I and the Janitor had when we were learning. At that time it looked like a very big puzzle. But now it did not.

"We may not be moving, but everything inside us is moving. The blood is flowing, the heart is beating. Our brain is working.All these are internal work and they will need energy. So even if we sleep continuously, we will still need food to keep us alive. Maybe, bears can last longer than us without food because they have evolved much more than us to reduce the energy needs."

I stopped again.

The class was silent. The teacher looked at me for a long moment. Maybe he did not expect me to answer the question..

"Ok," He said finally. "Now tell us about different forms of energy."

I went to the board and wrote some forms of energy

Different energies of a ball

1. Kinetic Energy - energy due to movement of ball

2. Potential Energy - energy due to how high the ball is

3. Heat Energy (or Thermal Energy) - energy due to how hot the ball is

My hand started shaking as I wrote the next energy type.

4. Chemical Energy

I had not understood what is chemical energy or how Petrol, when it burns in air, gives us energy. I hoped I can bluff my way through it or the teacher would ask me to stop before I came to it.

"First, Let us see kinetic energy" I said.

"No," the class teacher said. "Everybody knows about kinetic, potential energy. Why don't you explain about heat energy and chemical energy?" He asked.

"Sure," I said and walked back to the board. But I was not sure inside at all.Only heat energy remained between me and the public display of my ignorance. I better stretch heat energy topic till the end of the class or I would look like a fool.

"Thermal energy is the energy in an object depending on how hot it is. If you have a ball at 30 degrees and a ball at 40 degrees, the ball at 40 degrees has more energy," I said.

"Can you prove it?" The class teacher asked. "You said energy is the ability to do work, right? So can you show that a ball at higher temperature will push or lift more?" The class teacher asked.

I looked at him for a moment. I didn't know what he was trying to do. But I can't find fault because these were valid questions after all. Thankfully I knew the answer for the questions because of my sessions with the janitor.

"Let us try to take water first and show how hotter object does more work," I said.

I told them about an experiment which was done by 8th graders in every school. It involves taking three jars of water at different temperatures - one is freezing cold water, another at room temperature and the last one boiling hot. Then you just add a couple of drops of food coloring and wait for two minutes. The color would have completely spread throughout the jar with boiling water. The color would have not mixed so well in the water at room temperature and at the jar with cold water, no mixing would have taken place.

"Can you guess why such a thing would happen?" I asked the class.

There were different answers, but none of them correct. We had all done the experiment, but not learned anything. Neither had I, till I and janitor tried to understand work and energy.

"Well, the water in all three jars look to be at rest. But if you can see the molecules of water in three jars, you will see that they are moving at different speeds. The hotter the liquid, the faster the molecules will be moving. In fact, thermal energy is nothing but kinetic energy of the molecules."

Then I asked them whether they can explain why the food color spread faster in hotter liquid. This time they answered it correctly.

"The faster the water molecules are, the harder they hit the food color molecules and make them move," they said.

I agreed with them. We had proved that the hotter water does more work than colder water because it had moved the food color more.

"I can imagine molecules of water and air moving faster when they are heated. But how can molecules of solid move faster? They don't move at all. That is why they are solid, isn't it? Bhumika asked.

Well, honestly I didn't know Bhumika imagined. I thought she just memorized. But what she asked was a valid question. The molecules of solid don't move around like liquid and gases.

"You are right. The molecules of solid don't move around. They remain at the same place. But they jiggle or vibrate at the same place. Hotter the object, harder they vibrate. So hotter solids have more energy," I said.

"Let's move on now. Can you explain chemical energy?" The class teacher asked and my heart skipped a beat.

I walked slowly wondering what to do when a miracle happened. The class bell rang.

The class teacher got up and came over to me.

"You will explain chemical energy tomorrow," he said. "So better be prepared."