Showing posts with label Heat Transfer. Show all posts
Showing posts with label Heat Transfer. Show all posts

Dandelion Curls

It's spring in the northeast and that means (at least in my yard): Dandelions!

Did you know you can use dandelion stems to teach a simple (and pretty fun) lesson in osmosis as well as introducing the terms hydrophilic and hydrophobic?

Separate the stem from the flower and pull the stem into long strings.

Drop the strings into a tub of water and watch the stems curl up into all kinds of fun shapes! 

 If you drop the stem pieces one at a time, you can actually watch the curling process take place within just a minute or two.  Or you can dump a whole bunch in and have fun sorting through the results!
 What's happening?

The inside of the stem is hydrophilic, which is sometimes referred to as water-loving.  It's the part of the plant that absorbs the water.  And when it's placed into a tub of water, there's a whole lot of water to absorb!  The water moves into the cells through the process of osmosis. 

The outside of the stem is hydrophobic - it repels water.

The cells that make up the inside of the stem absorb so much water that they swell up.  The cells on the outside of the stem stay the same size.  The increasing size of the cells on the one side of the stem forces the stem into curls of various shapes.  



There's definitely something fun about sitting outside on a warm day and watching the curls form!  And if you can't be outside, grab some dandelions on your way to school and bring a bit of the outdoors in for your students.   

PS The idea of one side expanding more than the other side is similar to the way a bimetallic strip in a thermostat works.  The expansion is caused by temperature instead of water movement and it isn't as drastic as this, but it's conceptually similar. 

Goldilocks & the Three Bears:


Goldilocks and the Three Bears is a well-known fairy tale and provides a great opening for scientific inquiry. 

Whatever version of Goldilocks and the Three Bears you prefer, you'll come to the spot when Goldilocks goes to eat the porridge.  She finds that Papa's porridge, in the largest bowl, is too hot; Mama's porridge, in the middle-sized bowl, is too cold; and the Baby's porridge, in the smallest bowl, is just right. 

Does this part of the story make sense, scientifically?  Would the largest vessel keep something the hottest?  What about the smallest vessel keeping it warmer than the medium-sized one? 

It's easy to test it out for yourself!

You'll need 3 jars/bottles/beakers, each a different size.  If I were at school, I would use three different sized beakers.  Because I'm working from home, I used three different sizes of Mason jars: a quart jar, a pint jar, and a half-pint jar.  You'll also need a thermometer.  I used a candy thermometer, because that's what I had at home. 

Fill each of the jars with hot water.  However hot you can get it to come out of the tap is fine, it's not necessary to heat it further. 

Take a temperature reading right away, so you know your starting point. 

For younger students:
Set a timer for 15 minutes and when it sounds, take a temperature reading for each jar.  If you wish, you take an additional reading after another 15 minutes.

For older students:
Have the students, working in lab groups, take and record the temperature of each jar of water at regular intervals (1, 2 or 3 minutes).  These students can then graph their data, which will show the rate at which heat is lost from each vessel. 


I started with water that was 125 degrees Fahrenheit.  After 15 minutes, I had the following data:
Papa (Quart jar): 115 degrees
Mama (Pint jar): 109 degrees
Baby (Half-pint jar): 100 degrees

After completing the activity, graphing and drawing conclusions, students can re-write the tale, incorporating what they learned from the lab.

Summer Science Camp: Don't Melt the Ice Cube

See who can engineer the best icebox.

For this activity, I like to have students begin with uniform boxes, but it probably isn't crucial.

The students will each be given an ice cube their goal is to keep as much of the ice cube frozen as is possible.  I place each ice cube in a small zip-top bag in order to contain the water, which allows you to record quantitative data, as well as contains the mess.

I lay out all sorts of materials for students to use in their icebox creation:
  • fabric
  • yarn
  • newspaper
  • aluminum foil
  • waxed paper
  • plastic wrap
  • cotton balls
  • balloons
  • napkins
  • markers
  • wood shavings
  • packing peanuts
  • cotton batting
  • anything else you find lying around

The students can use the materials in any way they see fit - to wrap around the outside of the box or place inside the box with the ice cube.  Make sure the students' initials are located on the box somewhere. 

After the boxes are complete and the ice has been placed inside, the boxes are taken outside and placed in a shady spot.

After an hour (or other designated period of time) has passed, return the the boxes and observe the ice cubes.  For older students, you can pour off the melted water and measure it to determine who had the least ice melt. 

This activity could be added to your Water Fest, or done independently.

If you'd like to do this activity with your class, but it's the middle of winter, you could place the boxes under a heat lamp.  Or, just leave them sitting in the classroom (but you'll want to wait longer than an hour before checking on them).

Heat Transfer: How Does it Feel?

A basic tenet of the study of thermodynamics (that's right, I said thermodynamics.  It's a big scary word, but really it just means anything having to do with the transfer of heat.  Of course, there's a whole lot more about it - you can spend semesters studying thermodynamics, but there's nothing wrong with calling your study of heat transfer thermodynamics.  In fact it'll make everyone involved feel that much more important) is that heat/energy flows from higher temperatures to lower temperatures.  Here's a way you can actually feel that principle at work.

You'll need three bowls:
--Fill one bowl with water and allow it to sit for about 5 minutes (or more) to reach room temperature.
--Fill the next bowl with water and add several ice cubes.  Stir.
--Fill the final bowl with warm tap water.  Aim for something that just feels warm on your wrist - you don't water so hot that it'll hurt you.

Arrange the bowls on the table so that the room temperature water is in the middle and the hot and cold water are on either side of it.

Place one hand in the warm water and the other hand in the cold water.  Leave them there for about 20 seconds. 

Remove your hands from the bowls and place them both in the middle (room temperature) bowl.  How do they feel?

Even though they are now in the same water, the hand that was in the cold water feels warm and the hand that had been in the warm water feels cold.  Why?

You placed your hand in warm water.  The energy (heat) moved from the water, which was hotter than your hand, to your hand, making it feel warm.  Then you placed it in water that was colder than your (now warmed) hand.  The energy (heat) left your hand and flowed into the water, leaving your hand feeling cold.


You placed your other hand in cold water.  The energy (heat) moved from your hand into the cold water.  When you placed that hand, with a reduced amount of heat energy, in the room temperature water, energy (heat) flowed from that water to you hand because there was more energy in the water than your hand.

Layered Water

This is a lovely demonstration of the way water's density differs with temperature and convection currents (you don't actually see the currents, but you see the end result).

Allow a pitcher of blue-colored water to cool in the refrigerator overnight. 

At demonstration time, prepare a pitcher of hot tap water.  Color this water yellow.

Fill a jar (or cup) all the way with blue water.  Fill an identical jar all the way with yellow water.

Place an index card on top of the blue jar.  Carefully turn the jar over and set it on top of the yellow jar - make sure the rims line up.

Ask for hypotheses as to what will happen when you slide the card out.  Slide the card out -- the blue water sinks, mixing with the yellow, creating green water.


Now try again....
Prepare the jars in the same way.  But, this time, place the index card on the yellow jar, and place the yellow jar on top of the blue jar.

Remove the card and watch.....

You'll get a little green water right at the interface, but the yellow and blue water will mostly remain separate.


Why did you get two different results? 
Cold water is denser than hot water - it sinks.  When the cold water was on top of the warm, it sank to the bottom of the vessel, mixing with the warm, as evidenced by the mixing of colors.

When the cold water was on the bottom, it was content to stay right there.  Just a little mixing occurs right where the two temperatures meet.  What do you think would happen if you allowed it to sit for awhile?  Would the colors remain separate, or would they eventually mix?

Convection: Shavings in Boiling Water

Fill a larger beaker with water.  Empty your pencil sharpener into the water.  Give it a stir to mix in the pencil shavings (some of them will still float - that's okay).

Place the beaker on a hot plate and turn it on.  The beaker needs to remain on the heat source throughout the entire demonstration.

As the water gets hot, the pencil shavings will make the normally invisible convection currents visible.

The water at the bottom of the beaker is heated.  It then moves to the top of the beaker and the cold water sinks to the bottom of the beaker.  This water is then heated and moves to the top and cooler water sinks to the bottom.  This continues on and on, first heating all of the water, and then maintaining a consistent temperature.

Convection: Spirals over a Lightbulb

For this demonstration, you'll need a functioning lamp, shade optional.
You'll also need to cut a spiral out of construction paper and add a string so you can hold on to it.

FYI: This spiral was WAY too long (or my arm is way too short....) - I cut about half of it (the spiral, not my arm) off. 


First, hold the spiral above the lightbulb with the lightbulb off. The spiral will pretty much just hang there (it might spin around at first, if your string was twisted, but once it's settled, it should stay put).




Then turn on the lightbulb and hold the spiral above it again.  This time, the spiral will spin, and continue to spin. (I realize the picture below is useless, as you can't see it move, but it is, I promise). 


The lightbulb is heating the air above it (a by-product of converting electrical energy to light energy).  The warm air rises and cooler air sinks - a convection currect.  This moving air spins the spiral 'round and 'round.
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