It'll Get Cold Faster

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Status: Finished  |  Genre: Other  |  House: Booksie Classic
A brief explanation of the principle of heat (energy) transfer in layman's terms.

Submitted: February 21, 2015

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Submitted: February 21, 2015

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“It'll Get Cold Faster”

by: Liam O'Riley

I was at my best friend's house with my wife, Betsy.  Jim and Marla Newton had people over every Sunday.  It was a combination cook-out, extended play date for the kids, and a social day for the adults.  The Newtons backyard was something of a amusement park for the children.  There was an in-ground pool with a slide and a diving board, a trampoline with a safety net, a big sandbox, the longest Slip 'N' Slide I've ever seen, and half a dozen of those plastic castles and houses.  Toys were scattered from one end of the yard to the other.  There had to be twenty kids playing in and around the plastic houses, running around, swimming, slipping and sliding down the Slip 'N' Slide, jumping on the trampoline, and making a lot of happy kid noise.  Their ages ranged from about two years to around sixteen years old.
 Later, once the majority of children were asleep or settled down in front of the TV, there was often a Poker game or Blackjack.  Betsy didn't like to play that much, but I enjoyed losing some money from time to time.  And Betsy enjoyed socializing with both the other adults and the children that were still awake.
 Betsy and I didn't have any children of our own.  On the other hand, we've always been Uncle Shawn and Aunt Betsy to Jim and Marla's two kids in addition to our (and The Newtons) other friends' children.  There were several other people there; some we already knew and some we had just met.  Of course, the names of the people we'd just met slipped out of my mind, but that was typical of me.  I remembered their children's names, which is also typical for me.  It might have something to do with being a school bus driver.  Child's names stick in my mind and their parent's do not.
 We were sitting around the glass-topped table on the deck and I was telling some of the funnier stories about not quite making it through Engineering School at the University of Iowa.  I had changed my Major from Engineering to Partying during my third year.  Ultimately, it wasn't such a great idea.  It was, with the exception of a few embarrassing moments, a lot of fun at the time and it made for some funny stories to tell people these days.  However, they don't hand out degrees for Partying.  At least not from the University of Iowa.
 I heard the back gate squeak as it opened and a few people came through.  There were two women and a man; none of whom I recognized.  One of the women was carrying an obviously empty cooler since she was carrying it by one handle.  It bumped against her leg as she walked.  The second woman was carrying two big bags of ice and the man was carrying two cases of local beer, fortunately one of the really good ones.  The three of them came up onto the back deck.  Jim made introductions, which I promptly forgot.  They filled the cooler by layering the ice and beer.  Little ice; little beer; little ice; little beer.
 Once it was filled, the woman who had been carrying the ice said, “This is going to take forever to get cold.”  She spoke quietly, staring down at the cooler.
 Without thinking about it, I said, “Fill it with water.”
 She turned to me and said, “What difference does that make?”
 I hesitated before answering and glanced at Betsy.  She was looking at me with an expression that I'd seen many times before.  It basically said Please don't drag it out.  I shrugged slightly and, speaking in a prison whisper that only she could hear, I said,  “That will be up to her.”
 I turned back to to the woman.  “How detailed an answer do you want?”
 She gave me a challenging smile.  “As detailed as you can make it,” she said.
 Betsy rolled her eyes (I didn't see her do so since I wasn't looking at her, but I didn't have to.  We've been together for a long time).  With a sigh, she scraped her chair back and said, “Now you've asked for it.”  She walked down the steps of the deck and into the back yard.  She crossed the yard, going to the fence around the in-ground pool to watch a half a dozen children playing in the pool.  I could see her talking to Marla who was playing Life Guard.
 “Well?”  The woman asked.  She sat in a chair on the other side of the patio table.
 “Okay.”  I shifted into a more comfortable position.  “First, technically speaking, there is no such thing as warming or cooling.  It's simply the transfer of energy at the molecular level from one object to another.  Heat is a form of energy so the amount of molecular energy in an object rises with the temperature of the object.  Energy always goes from the warmer object to the cooler object.”  I raised my eyebrows.  “With me so far?”
 She nodded.  “The level of energy balances.  That makes sense.  That's why I put the beer in with the ice.”  I could clearly hear the “Duh” in her tone of voice.
 “Exactly,” I said.  “But that's just the set-up.  And there's a little bit more.  Keep in mind that the actual question is. 'Why does ice water cool the beer faster than ice alone?'”
 She nodded and glanced at the cooler.  Then she looked back at me.  “Go on,” she said.
 “Okay.  Keep that in the back of your mind.  We'll come back to that later.”  I paused.  “I'm sorry.  I don't mean to sound condescending.”  She shook her head and made a circling gesture indicating me to continue.  “Let me know if I do.  When I do.”  I paused for a moment to gather my thoughts.  “The next part has to do with density.  Everything has three basic states:  Solid, liquid, and gas. For almost everything, solid is the most dense, liquid is less dense than a solid, but more solid than a gas, and finally gas is the least dense.  There is one exception and we'll come to that later as well.”
 She smiled a particular smile.  “You should be a teacher,” she said.
 “Thought about it.  Driving a school bus pays better now that I have seniority and I only have to deal with kids for about thirty minutes at a time.  And I don't have to spend my money on school supplies”  I waved dismissively and went back to what I was saying.  “Air has a certain number of molecules per square inch.  Honestly, I don't remember what the actual number is any more and it does vary from one element to the next.  However, for this sake of the discussion, let's say it's one thousand molecules per square inch.  For a liquid, let's say it has ten thousand molecules per square inch.  For most solids, let's say it's, one hundred thousand molecules per square inch.”  I smiled.  “The one exception to that rule is water and ice.  Ice is actually less dense than water, which is why it floats.  So, let's say that ice has five thousand molecules per inch.-”
 She interrupted me.  “So that's why water and ice cool faster than ice alone.”  She looked smugly sure of herself.
 I smiled back at her.  “In part, but the question now is how?”
 Her smile slowly faded as she thought about it.  “I don't know.”
 “It's due to the rate of energy transfer and the amount of surface contact.”  I pointed at the cooler.  “Hand me a can and a couple of ice cubes.”  She looked at me for a moment and then leaned over.A moment later, she handed the can to me and reached down again.  A couple of ice cubes slid across the table.  “Thanks,” I said.  I left the can where it was and idly played with the ice cubes as I talked.  “The heat energy is transferred through the surface contact at the molecular level.  The heat energy- temperature- of the can of beer- the metal of the can and the beer itself- is higher than the surrounding air in the cooler and the ice touching the can.
 “The molecules in all of them are constantly moving.  Bumping into each other and to the edges of each of the objects in this example- ice, air, beer, beer can.  If the molecules bumping into each other are the same temperature, or energy level, if you prefer, the same amount of energy is transferred from one molecule to the other.  Therefore, no change of heat energy or temperature.  If the molecules are of different temperatures-”
 “Or energy levels.”  She said.
 “Gold Star for you,” I said, smiling and nodding.  “The energy of the warmer object gets transferred to the cooler object.
 “So.”  I went on.  “Energy goes from warm to cool.” I picked up one of the ice cubes and placed the corner of the ice cube against the side of the can.  “The energy is transferred at the lowest level of molecular density.  Where the air surrounds the can, energy is transferred at a rate of, in our arbitrary example, at one thousand molecular interactions per square inch.  In the small area where the ice cube touches the can, energy is transferred, again arbitrarily, at five thousand molecular interactions per square inch.  And finally, if you fill the cooler with ice water, the water transfers the energy at a rate of molecular interactions of ten thousand per square inch.”
 She stood up.  “Keep talking.”  She smiled.  “I'm going to get the hose and fill the cooler.”  She went to the corner of the deck and pulled the hose off the reel.  She went over to the cooler and fed the hose in.  I leaned over to the spigot and turned it on.
 “There isn't much more.”  I admitted.  “There's only a couple of other things I have to add.  With just ice and air, the ice is below freezing and the air is warmer, though eventually it does cool down until the cooler is opened.  Then the warm air outside the cooler mixes with the colder air inside the cooler and then the temperature rises.”
 “Because of the energy transfer at the molecular level?”  She glanced up with her eyebrows raised.
 “Actually, only a little bit at first.  When you open the cooler top, there's a pressure inversion and warmer air is pulled into the cooler.  The warmer air pushes out the cooler air.  When you close the cooler again, The warm air, cool air, and ice all transfer energy back and forth until the temperature- the energy level- is balanced again.”  The cooler was full of water.  Ice and beer cans floated to the top of the water.  I leaned over again and turned off the spigot again.  “The cooler air that escaped the cooler quickly rises to the ambient temperature due to molecular interactions and solar radiation.
 “When you mix ice and water,  The ice warms and the water cools quickly to the freezing point of water and stays there until all the ice is melted.  And it doesn't matter how often the cooler is opened.  Also, the ice only contacts the cans here and there so the higher rate of transfer is limited to certain spots.  However, when you fill the cooler with water, the water surrounds the can completely so the highest rate of energy transfer is the entire surface of the can.”
 Betsy stepped on the bottom step of the deck.  “Are you done yet,” she asked and I nodded.  The woman I had been talking to gave Betsy a look.  Betsy smiled,  “I've heard this a few times before.”  She shook her head and added, “He could have just said, 'It'll get cold faster.'”


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