A Conversation about Evaporation

One of the most challenging parts of teaching gifted students is getting a clear understanding of what these students know and understand.  Oftentimes, they have the vocabulary or understanding to some degree about a topic, but when you start to really ask what some words mean, you start to see the gaps.  Today, we watched a Magic School Bus video about the water cycle.  Afterwards, the class was explaining what they learned from it and used the words evaporation and condensation.  However, as I questioned further, I could tell from the conversation that they didn't really get how evaporation occurs.  Below is the conversation I recorded and scribed prior to conducting and experiment to determine the weight of hot vs. cold water.

As you read through this conversation, you will see that the students were relying on personal experiences, and things they have seen on TV, but didn't really understand why it happened that way.  Talking to each other was getting them closer and closer to the cause of evaporation, and we observed it in action to confirm our ideas at the end.

What was the big idea from this video?

AS: To learn what rain does.  First it evaporates, then it turns into clouds, then it goes back down, then it evaporates again and does it all the time

LR: first it starts out as water, then it evaporates, then it turns into a gas and then it goes up into the clouds, then it turns back into water to form the clouds, then it forms back into water and it drops down over and over again

What is our understanding of evaporate?

JL: to go from a liquid to become a gas

What needs to happen for evaporation to occur?

GH: It needs sun

LR: rain

CW: liquid

TV: sun, some clouds, some rain and needs to be water

What is the sun’s role?  How does it go up?

CW: It grabs with an invisible force and pulls it up

AS: It goes up because it needs to form clouds

TV: the sun brings it up

JL: an updraft

LR: a force

VK: a magnetic force

AS: The gas floats up because that’s the way it goes

CW: I know.  Water doesn’t weigh anything.

LR: Yeah, everything weigh something.

CW: Then how can you put your arms up so easy like this (waves his arms)

Mrs. Van:  you think this is no big deal (I wave my arms).  What is the difference in mass?

CW: Oh I get it, my arm is very strong and the air isn’t strong.

Mrs. Van: We have good ideas, but why does it go up?

TV: Because it’s cold up there?

LR:  Heat! Heat! Heat!

Mrs. Van: What about heat?

LR: Heat is a gas, and so it pulls, like a force and the gas and force interacts together and pulls it up

AS: The heat is really light so it brings it up to the sun, not really though…

AM: I think its actually gravity still

Mrs. Van: I think we need to find out what is heavy, hot or cold.

AS: In weird but true, it says that if you hit a baseball goes faster in hot air than in cold air.

Mrs. Van: Why?

AS: I don’t know!

TV: Because it’s heavier.

Mrs. Van: Here’s a chance to think like a scientist.  We have watched the video, talked about it, and now I have a question: Which is heavier, hot or cold?