Author: Maddie Van Beek

Summer might be over, but there are still plenty of warm days left to spend outside! Today we are going to make our own sidewalk chalk! Before we start creating, let’s learn about the science of chalk.


What do you think of when you hear the word chalk? Many of you might think of the thin white stick that you use to write on a chalkboard. Or you may have memories of colored sidewalk chalk that you play with outside. Those types of chalk are manmade, but did you know that chalk actually appears in nature? Check out the examples below!


Where does chalk occur naturally?

What is chalk? 
These chalk deposits have built up over many, many years. There are other chalk formations around the world such as the chalk cliffs in Germany and Denmark. Believe it or not, chalk is actually a rock. It’s just soft enough that you can use it to write with. Chalk is made of a substance called calcite, which is actually a form of the mineral limestone. The scientific way of denoting calcite (or calcium carbonate) is CaCO3. While blackboard chalk used to be made of this same substance, it is now usually made of gypsum, or calcium sulfate. That is what you’ll be using to make your sidewalk chalk today. 


Now that you know a little bit about chalk, let’s get started! ​

YOU WILL NEED:

• Toilet paper tubes
• Scissors
• Duct Tape
• Bucket or large mixing bowl
• Wax paper
• Water
• Tempera paint (available at Target, Amazon, and most craft stores)
• Plaster of Paris (gypsum)
• Cookie sheet

Here’s what to do! 

1. Collect about six toilet paper tubes. This is what you will use for your chalk mold. Cover one end of each tube with duct tape. Make sure the tape is secure so none of your chalk mixture will leak out the end. 
2. Measure a 6x6 inch piece of wax paper and cut it out. Roll the wax paper square up and place it inside the unsealed end of one of your cardboard tubes. The wax paper is to keep your chalk mixture from sticking to the inside of the cardboard tube. 
3. Repeat step 2 until you have all six of your paper tubes lined with wax paper. 
4. Measure out 3/4 cup of warm water and pour it into your bucket. 
5. Measure 1 1/2 cups of plaster of Paris and sprinkle it into the warm water. Stir as you sprinkle. The plaster will begin to harden in the next half hour, so you will want to work quickly. 
6. Divide the plaster of Paris mixture into six different bowls. Pick six different colors of tempera paint, and add about 3 tablespoons of paint to each bowl. Stir until the color is evenly distributed. 
7. Place each cardboard tube tape-side down on a cookie sheet, then pour the colored plaster of Paris mixture into each tube (one color per tube). 
8. Move the sheet of tubes to a place where they won’t be disturbed. It will take about three days for the chalk to dry completely. Peel the tubes and wax paper off, and voila! You have your own homemade sidewalk chalk! 

References
Vacker, M. Homemade sidewalk chalk. PBSParents: Crafts for kids. http://www.pbs.org/parents/crafts-for-kids/homemade-sidewalk-chalk/
Chalk. Wikipedia. https://en.wikipedia.org/wiki/Chalk

Images and Video Credits, in order of appearance: 

Taichi, 2005. The needles. Image uploaded from Wikimedia Commons on 8/28/2016. https://en.wikipedia.org/wiki/Chalk#/media/File:The_Needles.jpg File used in accordance with the Creative Commons Attribution-Share Alike 3.0 Unported license. No changes were made.

Yuvair, 2008. "Nitzana Chalk curves" situated at Western Negev, Israel are chalk deposits formed at the Mesozoic era's Tethys Ocean. Image uploaded from Wikimedia Commons on 8/28/2016. https://en.wikipedia.org/wiki/Chalk#/media/File:Nitzana_chalk_curves_(2),_Western_Negev,_Israel.jpg File used in accordance with the Creative Commons Attribution-Share Alike 3.0 Unported license. No changes were made.​

Tribble, 2008. Child drawing with sidewalk chalk. Image uploaded from Wikimedia Commons on 8/28/2016. https://en.wikipedia.org/wiki/Chalk#/media/File:Chalk-Sidewalk-Art-0092.jpg File used in accordance with the Creative Commons Attribution-Share Alike 3.0 Unported license. No changes were made.

Author: Maddie Van Beek

The past couple of weeks, you may have been watching the Olympics! It's pretty amazing to see some of the best athletes in the world compete! Of course, not all of us are at that level. So why is fitness important? Think about it. Sure, you have to be fit to do well in sports, but not everyone cares about sports, and that's okay! What’s the incentive to stay fit?

Facts about fitness:

• People who exercise frequently have healthier hearts. 
• Healthier hearts are less likely to have heart disease or strokes. 
• Exercising causes your body to release endorphins, which then make you feel better! Some runners describe this as a “runner’s high.” All I know is that whenever I’m having a bad day and I exercise, I am in a better mood afterwards! 

More reasons to exercise:

• Strengthens your muscles
• Improves mental health
• Strengthens heart muscles
• Counteracts unwanted weight gain
• Reduces some health risks, such as diabetes and depression
• Increases endurance and energy

​
There are many ways to determine fitness, such as VO2 max (oxygen used while exercising at capacity), flexibility, body fat percentage, etc. But today, we are going to focus on heart rate. 

Vo2 max testing:

Figuring out your resting heart rate and your heart recovery rate after activity is just one way to determine physical fitness, but it is a great start to making healthy goals for yourself. Heart recovery rate is “the time it takes for the heart to return to its normal resting beat” (NOVATeachers). While healthy hearts generally return to their resting rates rather quickly, unhealthy hearts can take much longer. 

Normal resting heart rates:

• Infants: 100-160 beats per minute
• Children 1-10 years old: 70-120 beats per minute
• Over 10: 60-100 beats per minute

How can you improve your heart health? ​

Sometimes the easiest way to improve is to make some simple goals. Here are seven ways to help keep your heart healthy.

Make a goal for the Life’s Simple 7s! Analyze how you are doing for each one now, and make a measurable goal for improvement in at least four categories. 

Now that you know a little bit about heart health and why it’s important, let’s test our resting heart rate! (Use the data sheet below to record your results)

Data sheet:

YOU WILL NEED

• Data sheet
• Partner
• Clock or stopwatch

Use this video to help you find your pulse if you have trouble:

YOU WILL DO

1. Place two fingers on the inside of your wrist to find your pulse. If you have a difficult time locating your pulse, place two fingers on your neck, just below your jaw. Whether you choose to use your wrist or your neck, continue to use the same spot for the rest of the activity, for sake of consistency.  
2. Have your partner watch the clock for 15 seconds. In those 15 seconds, you should count how many beats you feel. Record your results.
3. Repeat step 2 two more times. 
4. Average the three results, and then multiply by 4 to calculate your average resting heart rate in beats/minute. 

Next, you are going to figure out your heart recovery rate.


Predict: How long do you think it will take your heart to return to its resting rate? 


YOU WILL DO

1. Do 50 jumping jacks. 
2. Find your pulse in the same spot that you used earlier.
3. Have your partner watch the clock for 15 seconds while you count your beats.
4. Record in your data sheet in the column titled, “Pulse Rate (Beats per 15 seconds).”
5. Continue to take your pulse every minute for 7 minutes and record results in your data sheet.
6. Multiply each result by 4 to find your beats per minute for each minute recorded. Record in table titled, “Pulse Rate per Minute (Beats Per 15 Seconds x 4).”

Now, you are going to graph your heart recovery rate: 

1. Open Microsoft Excel, or other spreadsheet program, on a computer
2. Create two columns: one for time (in minutes), the other for Change in heartrate over your resting rate (in Beats per Minute).  Your spreadsheet will look something like this:

3. Enter minutes 1-7 in the left column, and the change in your heart rate for each minute in the right column, like the example below (your numbers may vary).

4. Use the spreadsheet to create a graph of your heart rate as a function of time.  If you are using Excel, just select all the data and the column headings, go to the “Insert” tab, and select the scatter plot option, with lines and markers.  Use the example below for guidance:

The graph you created should look something like this:

Extension: Push yourself!

1. Run one mile as fast as you can (if you don’t have access to a track, set a certain distance, such as around the block).
2. Find your heart recovery rate. 
3. Repeat weekly to see how you improve your time AND your heart recovery rate!

OR

1. Do as many pushups as you can.
2. Find your heart recovery rate.
3. Repeat weekly to see how you increase your number AND decrease your heart recovery rate!

Are there certain activities that you recover from quicker? Try out different exercises and compare recovery rates. 



Why does heart recovery rate even matter? How could having a slower recovery time affect you? 



References
https://en.wikipedia.org/wiki/Aerobic_exercise

http://www.pbs.org/wgbh/nova/education/activities/3414_marathon.html

http://www.heart.org/HEARTORG/GettingHealthy/GettingHealthy_UCM_001078_SubHomePage.jsp#

http://www.heart.org/HEARTORG/GettingHealthy/HealthierKids/LifesSimple7forKids/Keep-your-heart-healthy-with-Lifes-Simple-7-for-Kids_UCM_466541_Article.jsp

Images and videos, in order of appearance: 

Memorial Hermann, 2013. VO2 max test: What to expect. Uploaded from Youtube on 8/21/2016.  https://youtu.be/fn3Yr-LS_l0

Nova, 2007. Marathon challenge. Uploaded from pbs.org on 8/21/2016. No changes were made. 

eHow, 2009. Hospital basics: How to check your heart rate. Uploaded from Youtube.com on 8/21/2016. https://youtu.be/Wda4MeCSYyE

Excel images and instructions created by Dr. Erin Nyren-Erickson.

Author: Maddie Van Beek


What do you think of when you hear the word reaction?


Explosions? 


A rash? 


A response based on a previous situation or event? 


None of these thoughts are wrong, but today, we are talking about acid-base reactions. Check out the link below to define exactly what an acid-base reaction is.

FOLLOW UP QUESTIONS

1. What is an acid-base reaction? 
2. Why do acids and bases react and what happens when acids and bases react with one another? 
3. What compound is created from an acid-base reaction? 
4. Use a Venn Diagram to compare and contrast acids and bases. 

Learn more about Acid-Base reactions in this Crash Course video by Hank Green! 

Let’s check out our own acid-base reaction!

Make sure you do this experiment in the kitchen (or other easily cleanable area) or outside, if weather permits. 



YOU WILL NEED:

• Baking soda
• Vinegar
• Ziplock bag
• One square of paper towel
• Measuring spoons
• Measuring cups

Predict: What do you think will happen when you mix baking soda and vinegar in a sealed plastic bag? 



YOU WILL DO

1. Double check that your Ziplock bag has no holes. To test this out, fill it up with water and zip it up. If you see a leak, get a new bag. 
2. Create a “time-release” packet of baking soda. 
   1. Place your paper towel on a flat surface. 
   2. Measure 1.5 Tablespoons of baking soda and dump it in the center of the paper towel. 
   3. Fold the paper towel into a small square so that the baking soda is enclosed and will not leak out the sides. 
3. Measure 1/2 cup vinegar and 1/4 cup warm water, then pour both into the plastic bag. 
4. Now, you will need to move quickly! You may need a partner to help you out. You will need to hold your Ziplock bag open and place the time-release packet into the bag. The tricky part is that you need to zip the bag shut immediately after inserting the time-release packet. If you have a partner, have them put the packet in so you can focus on zipping the bag shut.  
5. Shake the bag up for a few seconds and then place it in the sink (or on the ground, if you’re outside). 
6. Record your observations!

What exactly happened and why?


EXPLANATION
Baking soda is a base and vinegar is an acid. When the two mixed together, there was an acid-base reaction! When the reaction occurred, it created carbon dioxide, which is a gas. The gas is what created those bubbles that blew up your Ziplock bag. 


Now that you have seen an acid-base reaction first-hand, you are going to try another one. This one will take a little longer to occur, so you won’t be able to watch the whole process.


YOU WILL NEED

• Two eggs
• Vinegar
• Two glasses
• Saran wrap
• A soup spoon

YOU WILL DO

1. Place one egg carefully inside each glass.
2. Pour enough vinegar to cover both of the eggs. You should see bubbles form on the eggs’ shells. Why?
3. Cover both glasses with saran wrap and put them in the refrigerator.  
4. Wait 24 hours.

Predict: What might the vinegar do to your eggs?

1. Use a soup spoon to CAREFULLY scoop the eggs out of the glass. What do they look like so far?
2. Dump the vinegar into the sink and then place the eggs back into the glasses.
3. Fill the glasses with enough fresh vinegar to cover the eggs, and place them back in the fridge for 24 more hours. 
4. Once again, use a soup spoon to carefully remove the eggs from the glasses. 
5. What do the eggs look like now?!

WHAT HAPPENED?
The eggshell is made up of calcium carbonate, which is a base. Referring to the experiment you already did with baking soda and vinegar, what do you think happened when you put the eggs into vinegar? Why? How was this experiment similar or different from the one above? 



Extension: Learn about Osmosis! 

Now that you have two shell-less eggs, let’s try a new experiment with them as an introduction to osmosis.

FIRST: What is osmosis?

A hypertonic solution has a higher concentration of solute outside the cell, therefore less water, than in the cell, while a hypotonic solution has a lower concentration of solute outside the cell than in the cell. 


An isotonic solution is “at peace.” It has an equal amount of solute outside the cell than inside the cell.


What is solute and what is a solution? 

An example of a solution is sugar water. The solute (substance to be dissolved) is the sugar and the solvent (the substance doing the dissolving) is the water. 
​

What does this all mean? 

Basically, a cell within a hypertonic solution will shrink, as the movement of water goes from the cell to the solution. A cell within a hypotonic solution will swell, as the movement of water goes from the solution to the cell. A cell within an isotonic solution will stay the same, as the water moves in and out of the cell equally. 


Check this science rap to help you remember these osmosis terms and learn more about where osmosis occurs in real life! ​

Let's start our activity!
Goal: See what happens when you put an egg in a hypertonic solution versus a hypotonic solution. 

YOU WILL NEED

• Two glasses
• Two naked (shell-less) eggs
• Corn syrup
• Water
• Soup spoon

CHECK FOR UNDERSTANDING

• Is the corn syrup hypotonic or hypertonic?
• Is water hypotonic or hypertonic?

Predict: How will your two eggs differ after hours? 


Here's what to do! 

1. Place each egg in a clear glass.
2. Fill one glass with enough water to cover the egg.
3. Fill the second glass with enough corn syrup to cover the egg. 
4. Place both glasses in the refrigerator for 24 hours. 
5. Take both glasses out and record your observations. 

What do your eggs look like? How do they differ? Why did this happen?


What do you think would happen if you now placed the eggs in opposite solutions? Try it out! 

1. Put the corn syrup egg in a glass of water and the water egg in a glass of corn syrup. 
2. Place in the refrigerator. What do they look like after 24 hours? 
3. Record your final results. 

References

• https://www.exploratorium.edu/cooking/eggs/activity-naked.html
• https://www.exploratorium.edu/cooking/eggs/activity-nakedexperiment.html
• http://www.exploratorium.edu/science_explorer/bubblebomb.html
• http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/acidbase.html
• http://www.microbelibrary.org/library/biology/3120-osmosis-a-cell-in-an-environment-that-is-hypotonic
• http://www.chem4kids.com/files/matter_solution.html

Image and video credits, in order of appearance:

CrashCourse, 2013. Acid-Base Reactions in Solution: Crash Course Chemistry #8. Uploaded from Youtube on 8/15/2016. ​https://www.youtube.com/watch?v=ANi709MYnWg&feature=youtu.be

Openstax, 2016. The process of osmosis over a semi-permeable membrane, the blue dots represent particles driving the osmotic gradient. Image uploaded from Wikimedia Commons on 8/15/2016. 
https://upload.wikimedia.org/wikipedia/commons/6/62/0307_Osmosis.jpg File used in accordance with the Creative Commons Attribution-Share Alike 4.0 International license. No changes were made. 

LadyofHats, 2007. Effect of different solutions on blood cells]]. Image uploaded from Wikimedia Commons on 8/15/2016. ​
https://upload.wikimedia.org/wikipedia/commons/thumb/7/76/Osmotic_pressure_on_blood_cells_diagram.svg/553px-Osmotic_pressure_on_blood_cells_diagram.svg.png File released into the Public Domain. 

Sciencemusicvideos, 2013. Osmosis! Rap science music video. Uploaded from Youtube on 8/14/2016. https://youtu.be/HqKlLm2MjkI

Author: Maddie Van Beek

Surface tension is a “contractive tendency of the surface of a liquid that allows it to resist an external force” (Wikipedia). These forces are a result of the hydrogen bonds water molecules form with each other (see our answer to “Why does ice float?")

Put the definition into your own words! What is surface tension?

Below, check out a water strider using surface tension to "walk on water." The surface of the water is like a thin membrane that resists the force of objects such as the water strider.

Check for understanding! 

• What are some other examples of times you have seen surface tension in action? 

• Why do water molecules at the surface create stronger bonds? 

• What is the surface tension of water? Does it ever change, and why? 

• What is the difference between cohesion and adhesion? 

• When you add soap to water, what happens to the surface tension? Hypothesize why this is.

Click HERE to learn more. 

Follow up question: 

• Why does the addition of soap cause the spring to sink? 

Let’s try out a similar experiment! 


YOU WILL NEED:

• Cup
• Water
• Paperclip
• A square of toilet paper

Extension Materials

• Soap
• Baby powder

YOU WILL DO: 

1. Fill the cup with water.
2. Hypothesize: Does a paperclip float or sink? 
3. Place the paperclip on the surface of the water. What happens? Record. 
4. Remove the paperclip from the cup. 
5. Gently place the square (or small piece of the square) of toilet paper on the surface of the water. 
6. Gently place the paperclip on the surface of the toilet paper. 
7. Watch what happens and record observations. How is this different than the first time you put the paperclip in the cup? Why is this? 
8. You should see the toilet paper absorb water and sink, leaving the paperclip “floating” at the surface!
9. What happens when you bend the paperclip? Do different shapes make any difference? 

Extension

1. Try what Physics Girl did in her experiment! Put a bit of hand soap on your finger and touch the surface of the water. What happens? Why is this? 
2. Next, hypothesize how many paperclips the surface of your cup of water can hold! 
3. We know that soap makes the surface tension weaker, but can anything make the surface tension stronger? Take a guess!
4. Sprinkle baby powder on the surface of your water, and try the paperclip experiment again. How many paperclips “floated” this time? 
5. Try out other liquids such as soda, milk, vegetable oil, vinegar... do you obtain the same results, or are they different? 

Resources

http://en.wikipedia.org/wiki/Surface_tension

http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html

http://www.sciencebob.com/experiments/paperclip.php

http://www.exploratorium.edu/ronh/bubbles/soap.html

​Image and video credits in order of appearance:

Apel, 2006. Water beading on a leaf. Uploaded from Wikimedia Commons on 8/8/2016. https://en.wikipedia.org/wiki/Surface_tension#/media/File:Dew_2.jpg File used in accordance with the Creative Commons Attribution 2.5 Generic license. No changes were made. 

Booyabazooka, 2008. Diagram of the forces on molecules of a liquid. Uploaded from Wikimedia Commons on 8/8/2016. https://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Wassermolek%C3%BCleInTr%C3%B6pfchen.svg/300px-Wassermolek%C3%BCleInTr%C3%B6pfchen.svg.png 
File released into the Public Domain. 

Vickers, 2008. Water strider. Uploaded from Wikimedia Commons on 8/8/2016. 
https://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Water_strider.jpg/1280px-Water_strider.jpg File released into the Public Domain. 
​
Billerbeck, 2010. Water strider or water bug.
​Uploaded from Youtube on 8/8/2016. https://youtu.be/b9nxUtoH7to

Physicsgirl, 2012. Amusing surface tension experiment. Uploaded from Youtube on 8/8/2016.
https://youtu.be/2F64qh9qPAI

Armin Kubelbeck, 2007. A metal paperclip floats on water. Uploaded from Wikimedia Commons on 8/8/2016. 
https://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Surface_Tension_01.jpg/1024px-Surface_Tension_01.jpg File used in accordance with the Creative Commons Attribution-Share Alike 3.0 Unported license. No changes were made.