A Hole in the Water

This is a very cool demonstration!  Make sure you only use a spoonful or two of water - I tried to do this repeatedly, but with too much water, and was getting very frustrated by the lack of results.  When I broke down and followed the directions, it worked beautifully.  I had to do it 3 times in a row just to marvel at it!  

Place a spoonful of water onto a plate.  Add a drop of food coloring and swirl to mix.

When the water has settled, add a few drops of rubbing alcohol to the center of the water.

Watch the water pull away from the alcohol - the alcohol has less surface tension than the water.  The water molecules want to stick together (literally), so they pull away from the alcohol, leaving a hole in the middle.

Watch the edge of the water.  It literally quivers as it tries to stick together.  So cool!

Atoms: Tasty Atomic Models

If you teach your students about the Thomson, Rutherford, Bohr and Heisenberg/Schrodinger models of the atom , you need to use this activity.  It's from Roseann McCarthy at Ocean Township High School, New Jersey and it's super fantastic.

Put your students in groups of four. 

Give each group a bag containing:
--A chocolate chip cookie
--A Tootsie Roll pop (or a Blow Pop)
--A Gobstopper
--A Ferrero Rocher chocolate

The students examine the candies/cookies and discuss which item best illustrates each model of the atom and why.

I like to have students explain why the item is a good model as well as provide a reason why it is not perfect and brainstorm ideas for other objects that would work to represent each atomic model.


Thomson - Chocolate Chip Cookie
Thomson described the atom as having negative charges scattered throughout it, like the cookie has chocolate chips scattered throughout it. 

Rutherford - Tootsie Roll Pop
Rutherford first proposed the idea of a nucleus.  The Tootsie Roll pop has a dense Tootsie Roll center, or nucleus.

Bohr - Gobstopper
Bohr placed electrons in energy levels, or layers outside the nucleus.  Gobstoppers change colors as the oustide dissolves because there are many layers of color.

Heisenberg/Schrodinger - Ferrero Rocher
The Heisenber/Schrodinger model places electrons scattered outside the nuclues - they care in a predictable space but no exact location can be identified.  The Rocher candy has a hazelnut center (nucleus).  In addition, there are chopped hazelnuts in chocolate surrounding the center - those pieces of nut are found in a specific region, but we can't pinpoint exactly where each piece of nut will be.

In case you aren't familiar with the Ferrero Rocher candies, here's a picture of one, cut through the middle:

At the end of the activity, I allow the groups to divide the items as they see fit.  Sometimes serious negotiations take place, but I've never has it turn into an argument (if it looks like it might, all you have to do is threaten to dispose of all the items for them).

A few more ideas/extensions:
--You can add Dalton's orginal atom as a sour ball or other piece of hard candy that's the same throughout.
--You might want to have a knife available, in case a group needs to cut one of the items open.  Keep it in your possession and you can do the cutting as directed by the group.
--If you can't bring candy into your classroom, take pictures of the candies and let the students work them out that way.  By using materials familiar to the students, they will develop a greater understanding of the models.  Going through the Ferrero Rocher model really helped me understand electron clouds better. 

Comparing Amino Acids & DNA

A quick review...
DNA provides instructions for the assembly of amino acids into protein.

Therefore...
Similar proteins have a similar amino acid sequence.  And if the amino acid sequence is similar, the DNA is similar.

Scientists believe that similar DNA sequences indicate a common origin.

Hemoglobin (a protein in red blood cells) is one protein that has been studied in humans, gorillas, and horses.


Procedure:
Each group will be given 10 different colors of beads (each one representing a different amino acid - see list below).

Students use the beads to create the partial amino acid sequence for human, gorilla and horse hemoglobin (see below).

For assembly purposes, I give the students an index card with three pipe cleaners attached.  It keeps it all in one place, and it makes it easy for the students to compare the sequences at the end.

After students have completed the amino acid sequences, I use my keys to quickly check their work.

They then count and record the differences in the amino acid sequence.

From there, you can discuss...
--what determines the order of amino acids?
--where do we get our DNA from?
--where did our parents get their DNA from?
--random chnages in DNA occur over time, the mroe time passes, the more changes there will be.

At the end of the activity, students remove thier beads and return them to their appropriate bag.


The Amino Acid Sequences:
Human: gly lys val asp val asp glu val gly gly glu lys leu his val asp pro glu asp phe arg leu

Gorilla: gly lys val asp val asp glu val gly gly glu lys leu his val asp pro glu asp phe leu leu

Horse: asp lys val asp glu glu glu val gly gly glu lys leu his val asp pro glu asp phe arg leu

******
This activity comes from a wonderfully creative and talented teacher who presented it in a workshop at the New Jersey Science Teachers Association Convention.  Unfortunately, I don't have her name written down.  If you know her, or are her, please contact me and I will give her all the credit in the world for this great activity!

Solar System: The Planets to Scale

Textbooks are notorious for completely out-of-whack drawings of the planets in our solar system.  They're about as out-of-whack as the solar system models made by 3rd graders - you know the ones, made from styrofoam balls.  The craft stores only sell about 3 sizes of styrofoam balls, so Jupiter ends about being about twice as big as Mercury and Pluto. And the sun is maybe a little bigger than Jupiter...

Remember these pictures?  They're a good place to start your discussion of planet size. 

But, why not add some props to make the lesson even more fun and memorable.

For each planet (and the sun) I'll give you the object I used, the planet's actual diameter and the scaled diameter (so you can take your ruler with you to the produce department in search of the perfect melon to represent Saturn). 

The Sun:

1,400,000 km --> 140 cm

1/2 plastic tablecloth

Mercury:

4,900 km --> 0.49 cm

peppercorn

Venus:

12,100 km --> 1.21 cm

mini-marshmallow

(in the pictures, I used a Gobstopper for both Venus and Earth because my marshmallow was missing)

Earth:

12,800 km --> 1.28 cm

Gobstopper

Mars:

6,800 km --> 0.68 cm

split pea

Jupiter:

143,000 km --> 14.3 cm

small (size 3) soccer ball

Saturn:

120,000 km --> 12.0 cm

melon

Uranus:

51,800 km --> 5.18 cm

baseball

Neptune:

49,500 km --> 4.95 cm

small apple

Pluto:

2,300 km --> 0.23 cm

sprinkle

I like to begin the demonstration by showing students the sun and then having them guess how big Earth would be at that scale; everyone holds up their hands to show me how big it would be.  They always think it's way bigger than it is! 

After revealing the Earth, we then go back to Mercury and work our way through all the planets in the same way. 

It's a good way to begin a discussion of Pluto's classification, as Pluto looks absolutely puny after those gas giants. 

Graphing & Extrapolating: How Many Licks Does it Take?

Last week, we started to find out How Many Licks Does it Take to Get to the Center of a Tootsie Roll Pop.  Last time largely focused on data collection, which is a great skill, but doesn't answer the question at hand. 

Since we weren't able to complete enough licks to get our answer, we need to graph the data and then extrapolate to find the answer.  You can do this by hand or using Excel. 

Here are the instructions for creating the graph on Excel*
Open a new excel worksheet

Label column A "Number of Licks"

Label column B "Mass"

Fill in number of licks, continuing by 10s until you reach 200 (yes, go to 200 even if you didn't get anywhere near that many licks done).

Fill in corresponding masses

Highlight the numerical data (don't include the column titles in your highlighting)

Go to Insert, then Chart

Click on XY Scatter, then click Next

Click Next

Enter a chart title (name of lab), the x-axis label (Number of Licks), and the y-axis label (Mass (g))

Click Next

Select the option to place the chart as a new sheet

Click Finish

Click on one of the points on the graph - all the points should be highlighted

Go to Chart, then Add trendline

Click Okay

Click on the legend and delete it

Double click on the numbers on the y-axis.

Click on Scale

Change Minimum to 0

Double click on the background of the graph

Set area to none

Print the graph

Draw a horizontal line at the value you had for the stick and wrapper

At the point where the line you drew hits the line on the graph, draw a vertical line to the x-axis.

Estimate the value for where the line hits the axis - that is the number of licks it would take to get to the center of a Tootsie Roll Pop



*I wrote these instructions using an older version of Excel, which is still what I have access to. If you use a newer version and find that some of the terminology needs to be changed, please let me know.  Also, please let me know if something is unclear or you just aren't sure about something and I'll do my best to help.

Action/Reaction: Spring Scale Demonstration

For this demonstration, you'll need 2 student volunteers and 2 identical spring scales. 

Hand each student a spring scale.  They'll hold the loop end with one finger.  Hook the opposite ends of the spring scales together.

Instruct one of the students to pull his/her spring scale with 10 N of force (or whatever number is appropriate for the spring scales you are using; something in the middle of the scale) and the other student to pull with 0 N of force (or 5 N or any number as long as it's different from the first student). 

Then let them try to do it.

When they can't get it to work, I usually step in and try to "help".  I have the one student pull the spring scale so it reads 10N.  Once that one's set, I tell the other student to then pull his spring scale to the predetermined number. As they're doing this, they'll notice that both spring scales are always at the same number, no matter what they do.






It's that whole "For every action there is an equal and opposite reaction" thing. If a student pulls on one scale with 10N of force, the other scale pulls with 10N of force (equal force), but in the opposite direction. 

It's a really simple demonstration, but it really exemplifies the "equal" part of Newton's third law. 

Body Systems: Respiratory System: Model Lung

Creating a model lung is pretty simple.  You can find directions all over the internet, including right here!

Start with a plastic bottle, any size will do.  (Pictured here is a water bottle, but 2 liter bottles work as well).

Cut the bottom off the bottle.  If you're having students make their own lung, you may want to do this for them, and if the students are young, you may want to tape over the cut edge so no one gets cut.

Place a balloon in the neck of the bottle, and stretch the opening of the balloon over the opening of the bottle  (see the blue balloon in the above photo).

Cut the narrow part off of a second balloon.  Stretch the remaining balloon over the bottom of the bottle.

That's it.  

Now to use it.... 

The blue balloon represents a lung.  The red balloon is the diaphragm.  

When you breathe in, the diaphragm contracts (pull the diaphragm balloon down).  This lowers the air pressure in the chest cavity (because there's more room) and air fills the lungs.

When you exhale, the diaphragm relaxes (release the balloon, you can even push up on it a little).  The air pressure in the chest cavity increases and air flows out of the lungs.