Author: Maddie Van Beek

What’s heavier: A pound of feathers or a pound of rocks? This is is a trick question! A pound of anything is the same weight as a pound of anything else, but it would take WAY more feathers to make up a pound than a pound of rocks. This has to do with density. 



Density is determined by how tightly the atoms in an object are packed together. An object with very tightly packed atoms is denser than an object with atoms that have more room in between each other. Take a look at the image below. Which is denser, object A or object B?

Think back to the example. A rock is much more dense than a feather, so one pound of rocks takes up much less space than one pound of feathers.  

We have learned about density in some of our previous blogs, such as when you built a a liquid rainbow in a jar using liquids of different densities. Check it out to learn more! http://discoveryexpress.weebly.com/homeblog/rainbow-in-a-jar-learning-about-liquid-density

An object that is denser is also heavier than an object that is less dense. For example, stainless steel has a density of 7.8g/cm^3. Aluminum has a density of 2.7g/cm^3. Because steel has a higher density, it is heavier, more sturdy, and is used to build objects that need to last a long time, such as bridges or ships, while aluminum, a lighter, more flexible metal, is used more to make items such as cans or baking sheets. 

A similar example is muscle versus fat. Take a look at the image below. Which is denser, muscle or fat? 

You can see that 5 pounds of muscle takes up less space than 5 pounds of fat. 

So let’s get back to our question of the day: Do bowling balls sink or float? The answer seems obvious, doesn’t it? Clearly, heavy objects such as rocks should sink while lighter objects such as feathers would float, right? Well, it’s not as simple as it may seem. A bowling ball seems pretty heavy, but the determining factor of whether the ball (or any object, for that matter) will sink or float is its density. If an object is denser than water, it will sink. If an object is less dense than water, it will float. Water has a density of approximately 1g/cm^3. Just how do you figure out an object’s density? Let’s find out!

Now that you know a little bit about what density means, let’s try our activity! You are going to find out what density of bowling ball will sink and what will float. Your task is to find out the densities of each bowling ball using the following equations:


Circumference equation: 

circumference = 2 * π * radius


Volume equation:

volume = 4/3 * π * radius^3

(Remember, the symbol π is pi. Pi is approximately 3.14)



YOU WILL NEED:

• Two bowling balls (one lighter than 11 pounds and one heavier than 13 pounds)
• Tape measure
• Pencil
• Bath tub or large container filled with water
• A scale

Here’s what to do!

1. Fill the tub or container with water. 
2. Predict whether the bowling balls will sink or float. Why do you think this? 
3. Place the heavier bowling ball in the water. What happens? Is this what you thought would happen? 
4. Place the lighter bowling ball in the water. What happens? Does this surprise you? Why or why not? 
5. Now that you’ve observed what happens with each ball, you are going to actually determine their densities. 
6. Use a tape measure to find the circumference of your ball. To find the circumference, you need to wrap the tape measure all the way around the widest part of the ball. Make sure the tape measure is flat against the ball. Every ball should be right around 27 inches. Once you measure the ball, convert the inches to centimeters. 1 inch = 2.54 centimeters. 

For example, if your ball is 26 and 3/4 inches, then you would multiply 26.75 by 2.54. 



26.75 inches x 2.54 = 67.945 centimeters



7. After you find the circumference, solve for radius. 



67.945 = 2 x 3.14 x r

67.945 = 6.28 x r

67.945/6.28 = r

10.819 = r



The radius is 10.819cm. 



8. After you find the radius, you can solve for volume using the volume equation. 



volume = 4/3 * 3.14 * r^3

volume = 4/3 * 3.14 * 10.819^3

volume = 5301.878cm^3



Now you have the volume of the ball... IF the bowling ball were a perfect sphere, but it’s not. Bowling balls have finger holes, so you need to find the volume of the finger holes and then subtract the finger holes volumes from the volume you just found. 



9. Use the volume equation for cylinders below: 

volume = π * radius^2 * height

To complete this equation, you need to find the height and radius of the finger hole. Find the height by sticking a pencil eraser-first into the hole until it hits the bottom, marking the point on the pencil at the finger hole’s top, then measuring the pencil from the eraser to the point where you marked it. This is your height. Let’s say you found out the hole was 2.5cm deep. Plug the number into the equation. 



Volume = 3.14 * radius^2 * height

Volume = 3.14 * radius^2 * 2.5cm



10. Next you need to find the radius of the hole. The radius is half of the diameter (width of the hole). Remember to measure in centimeters! Let’s say you found out the diameter of the hole was 1.2cm. Because the diameter is 1.2cm, the radius would be 0.6cm. Plug the number into the appropriate spot in the equation. 



Volume = 3.14 * .6^2 * 2.5

Volume = 2.826cm^3 



11. There! You’ve now found the volume of a finger hole in the bowling ball. Check to see if the radius and height of each hole is the same. If they are all the same, you can just multiply the volume you found for the first hole by 3. If they are different, find the volume of the other two holes and then add them together to find the total volume for the three holes. For simplicity’s sake, let’s say that all three holes were the same and multiply our first number by 3.



Volume of three holes combined = 8.478cm^3



Now that you have the volume of the finger holes, subtract this number from the volume of the ball that you found earlier. 



Volume of bowling ball - volume of finger holes = True volume


5301.878cm^3 - 8.478cm^3 = 5,293.4cm^3


True volume of the bowling ball = 5,293.4cm^3



12. Now you FINALLY have the volume of the bowling ball! BUT you still don’t have the density. To find the density, you need to weigh the ball. Remember to use a scale that measures in grams. If you don’t have one, 1 pound = 453.6 grams. 



If your ball is 13 pounds, then you would multiply 13 by 453.6. 

13lbs * 453.6 = 5,896.8g



13. Now that you have the weight, divide it by the volume of the ball in cubic centimeters to discover the density. 



Weight of bowling ball / True volume of bowling ball = density



5,896.8g / 5,293.4cm^3 = 1.114g/cm 

The density of your bowling ball is 1.114g/cm. 



There you go! You now know how to find the densities of the two bowling balls. Do your results match up with what you predicted earlier? You should have found that the ball that floated had a density of less than 1g/cm while the ball that sank had a density of more than 1g/cm. 




References

http://scifun.chem.wisc.edu/homeexpts/bowling.htm


http://the-science-mom.com/875/density-a-simple-explanation/


http://classroom.synonym.com/explain-density-16387.html


http://www.middleschoolchemistry.com/lessonplans/chapter3/lesson1


http://www.brighthubeducation.com/science-homework-help/52127-what-is-density/

Author: Maddie Van Beek

In past experiments, you’ve learned about acids and bases. For example, you learned about acid-base reactions when you made an eggshell disappear and exploded a plastic bag: http://discoveryexpress.weebly.com/homeblog/experimenting-with-eggs-acid-base-reactions-and-osmosis 




Since you already know about acid-base reactions, today we are going to learn how to test different substances to not only tell whether they are an acid or a base, but also determine their pH levels. 




Why is it important to test for pH? Just one reason that scientists use pH testing in the real world is to check the quality of the water you use. If your water is too acidic or too alkaline, it could be dangerous. 




How will we do this activity without a complicated test kit? You are going to make your own pH level test kit simply with red cabbage!

If the pH is at 8, what color will the red cabbage extract be? 




If the pH is at 12, what color will the red cabbage extract be?




Let’s test it out!




Before you can test any liquids for their pH level, you need to make your pH indicator. 




YOU WILL NEED

• Red cabbage
• Water
• Measuring cups
• Food processor/blender
• Strainer
• Bowl
• Small cups

Here’s what to do! 

1. Cut up a head of red cabbage into small pieces. Measure about 2 cups of red cabbage pieces and dump it into the food processor. 
2. Add 1 cup of water to the red cabbage in the food processor. 
3. Cover the cabbage and turn on the food processor until the cabbage is fully blended. 
4. Place a strainer over a bowl and dump the blended red cabbage into the strainer. 
5. Remove the strainer and set aside. You should now have a bowl of red cabbage extract. This is your pH indicator!
6. Now that you have your indicator, you can test some household substances for their pH levels. 
7. Label one small cup vinegar and add 1/2 cup vinegar. Label a second small cup baking soda and add 1/2 cup water and 1 teaspoon baking soda. Stir until the baking soda dissolves. Label a third small cup ammonia and add 1/2 cup laundry ammonia. 
8. Make a chart to track your results. Use markers to color your chart and then estimate the pH level based on the pH scale above. Your chart may look similar to the one below:

9. Add 1 teaspoon of pH indicator to each cup. Observe. What colors did each liquid change to? Record your results. 


10. Find other household substances to test out! See how many different pH levels you can find in your home. 



Here’s an example of substances you could test: 

References:

• http://scifun.chem.wisc.edu/homeexpts/ACIDBASE.html
• http://discoveryexpress.weebly.com/homeblog/experimenting-with-eggs-acid-base-reactions-and-osmosis
• http://chemistry.about.com/od/acidsbase1/a/red-cabbage-ph-indicator.htm

Author: Maddie Van Beek


Have you ever bounced a rubber ball? Think about that experience--what makes a ball bounce? Bouncy balls bounce because of the highly pressurized rubber. Rubber is a highly elastic material, which makes it bouncy, but is also a polymer. We have learned about polymers in some of our previous blogs, such as when you created homemade slime (http://discoveryexpress.weebly.com/homeblog/two-times-the-slime-fun-with-polymers) or when you pierced a balloon without popping it (http://discoveryexpress.weebly.com/homeblog/balloon-science). Check them out to have more fun with polymers! 




Before you understand a polymer, you must know what a monomer is. See the visuals below.

A monomer is a small molecule that is able to bond with other monomers to form a larger molecule, or polymer.




Mono = one

Poly = many 




A polymer is created when monomers undergo a chemical reaction and form a chain. Think of a polymer as a necklace and the monomers as the beads on the necklace. 

In your activity today, you will be using glue, borax, and corn starch as your special ingredients to create a bouncy ball. Glue has polymer molecules in it already, but when you add the borax, it cross-links the polymer molecules in the glue to create polymer chains. 

The corn starch that you mix in acts as a binding agent. Think of how the cornstarch helped you create your slime a few weeks ago. If you missed this blog, check it out here: http://discoveryexpress.weebly.com/homeblog/two-times-the-slime-fun-with-polymers. 



Now that you know a little bit about polymers and the ingredients’ purposes in your activity, let’s get started! 



YOU WILL NEED:

• Water
• Glue
• Borax
• Corn starch
• 2 small bowls or cups
• Spoons or stirring sticks
• Food coloring

Here’s what to do!

1. First, get organized. Label once cup ‘Borax Solution’ and one cup ‘Ball Mixture.’
2. Pour 4 ounces of warm water into the ‘Borax Solution’ cup and add 1 teaspoon of borax. Use a spoon to thoroughly stir the water and borax together until the borax dissolves. 
3. Pour one tablespoon of glue into the ‘Ball Mixture’ cup and add a few drops of food coloring. Use a second spoon or stick to stir the food coloring in. 
4. Add 1/2 teaspoon of the Borax Solution into the ‘Ball Mixture,’ then add 1 tablespoon of corn starch. DO NOT MIX. 
5. Wait about 15 seconds to let the ingredients interact. Observe. Can you see anything happening? 
6. Use a spoon to stir the ingredients in the ‘Ball Mixture’ cup together until the mixture becomes a solid substance that you can no longer stir. The ingredients should quickly form a ball. 
7. Remove the ball from the cup and use your hands to roll it into a sphere. It may start out a little messy and lopsided, but soon you’ll have a nice, round bouncy ball!

Extensions

1. Now that you’ve made the bouncy ball, test it out! What surface does it bounce best on? How high can you get it to bounce? 



2. Try changing the amount of borax, glue, or cornstarch. Test out several different combinations and test each ball to see what helps create the highest bounce. 



References

• https://sciencebob.com/make-your-own-bouncy-ball/
• http://www.theidearoom.net/2009/07/make-bouncy-ball.html
• http://www.pbs.org/parents/crafts-for-kids/super-bouncy-balls/
• http://www.brooklyn.cuny.edu/bc/ahp/SDPS/SD.PS.polymers.html

Author: Maddie Van Beek

Have you ever seen a lava lamp before? Your parents might have one left over from when they were teenagers! If you haven’t seen one before, take a look at the photo below! 

Lava lamps used to be super popular and seem to make a comeback every once in a while. The “lava” inside real lava lamps are made with colored wax, but today, you are going to make a much simpler version of the classic lava lamp using oil, water, and Alka-Seltzer tablets.

If you have been following our blog for a while, you may remember other Alka-Seltzer experiments we’ve done in the past. For example, you made film-canister rockets  (http://discoveryexpress.weebly.com/homeblog/make-your-own-film-canister-rocket) and made bubbles float (http://discoveryexpress.weebly.com/homeblog/make-soap-bubbles-float)! As you know from these experiences, Alka-Seltzer has a fizzy reaction that occurs when you place the tablet in water. When Alka-Seltzer fizzes, it is actually releasing carbon dioxide gas. Check it out!

Now that you know a little bit about Alka-Seltzer and its reaction with water, let’s move on to the other aspects of this activity. Before you use any Alka-Seltzer, you need to actually mix oil and water to start your project. 



As you might already know, oil and water do not like each other! Pour a glass of water and then add a drop of vegetable oil. What happens? The oil sits right on top of the water. You may have already known that oil and water don’t mix, but do you know WHY? Check out the video below for a little insight! 

Two main reasons that oil and water don’t mix are their different densities and charges. You might have already worked with liquid density when we made a liquid density rainbow. If not, check it out for more ways to learn about liquid density while making a liquid rainbow in a glass (http://discoveryexpress.weebly.com/homeblog/rainbow-in-a-jar-learning-about-liquid-density)!

Basically, water molecules are packed more tightly than oil molecules. When molecules are more tightly packed, they are denser than other liquids or objects that have molecules that are less tightly packed. This means you might have two objects of the same size that are different densities. 



Look at the image below. Which object is denser?

Because one object is denser, it will weigh more. For example, look at the picture below. Even though the cork and the rock are about the same size, the cork floats while the denser rock sinks to the bottom. 

Essentially, half a cup of oil and half a cup of water look the same, take up the same space, but a half cup of water contains more molecules than a half cup of oil. This is why when water and oil are mixed together, the oil floats at the surface and the water sinks to the bottom. 



The other reason that oil and water don’t mix is that water is polar and oil is non-polar. Because polar molecules only dissolve in polar solvents and non-polar molecules only dissolve in non-polar solvents, neither the water or the oil will dissolve when mixed together. Instead, the water molecules will stick to each other and the oil molecules will do the same. 



Now that you know a little background information on your materials, let’s get started! 



YOU WILL NEED: 

• Empty plastic bottle
• Water
• Oil
• Alka-Seltzer
• Food coloring
• Flashlight (optional)

Here’s what to do!

1. Fill your plastic bottle with vegetable oil until it is about 3/4 full. 
2. Pour water to your bottle until it is full, but not overflowing. 
3. Add about 10 drops of food coloring into the bottle. Take a moment to record your observations. What happened when you added the food coloring? Did it mix in with both liquids?
4. You should have noticed that the food coloring changed the color of the water but not the oil. Why do you think that is? 
5. Next, break an Alka-Seltzer tablet into a few pieces and drop one piece into the mouth of the bottle. What happens? Lava greatness!
6. If you want the full effect of the lava lamp, set your bottle on top of a flashlight and turn the lights off. 
7. As soon as the bubbling subsides, just add another piece of Alka-Seltzer to keep the party going! 

References

https://sciencebob.com/blobs-in-a-bottle-2/

http://www.stevespanglerscience.com/lab/experiments/bubbling-lava-lamp

https://www.questacon.edu.au/outreach/programs/science-circus/videos/oil-and-water

http://mocomi.com/why-oil-and-water-dont-mix/

https://en.wikipedia.org/wiki/Lava_lamp