SLOS - 8-3-08 - GLO: C2, D3 - Compare fluids of different densities to determine how they alter the buoyant force on an object.
Why I chose this topic?
I believe this topic is sometimes difficult for students to understand and so I chose a discrepant event that the students could relate to their everyday lives. Most students drink pop on a regular basis and would not expect that two cans of pop, which are the same size, will react differently when placed in water. Furthermore, I believe it is a great discrepant event because it will get the students thinking about how other pops would react when placed in water. They will realize you can learn a lot about the content of a pop can by whether or not it floats when placed in water.
When Coke Floats
“Hurry up!” Antonio screamed.
Frustration was starting to set in while he waited for Joel. They rode to school every morning together and just like every other morning Joel was late. However, Antonio, being the responsible one, anticipated this. He came early every morning because he knew Joel was slow and liked to make unnecessary stops along the way to school.
“Were gonna be late!”
“Okay! Okay! I’m coming! Would you relax!” Joel barked back.
It was a hot June morning. The humidity was so thick you could see it. Antonio was trying to hide from the sun by holding his skateboard over his head as he waited for Joel to come out his bedroom window. Even if he wasn’t leaving against his parents will Joel still used the window. He said he didn’t want to get sloppy with his technique on sneaking out the window and for a guy who snuck out of his window every single night this seemed to make sense. He had it down to a perfection. Antonio watched as he slithered out of his window feet first. He made sure he only stepped on certain areas of the roof before anchoring himself down the basketball hoop hanging on the garage. Perfection!
“I’m sweating already!” Joel complained. He looked over at Antonio and laughed. “Look at you! You’re soaked right through your shirt!”
“It’s not my fault its 300 degrees outside!” Antonio snapped.
“Come on, let’s go buy a cold drink on the way to school.” Joel said while patting him on the back.
They jumped on their skateboards and rode down the newly asphalted street. The heat made it feel like their wheels were sticking to the roads surface.
They stopped off at the corner store to pick up a couple cans of coke. They pressed the cokes against their foreheads as they walked out of the store. The ice cold cans were refreshing as they pressed against their skin.
“Come on, let’s go drink them down by the quarry. We could even take a quick dip before school!” Joel blurted out with excitement.
Antonio knew this was a bad idea but of course that was typical coming from Joel. However, despite his fear of being late for school Antonio quickly submitted and agreed to go. The heat was unbearable and the thought of jumping into cool refreshing water was just too good to pass up.
“Alright, but we have to be quick!” Antonio demanded.
It didn’t take long before they reached the quarry. Joel jumped in first. Antonio piled their clothes and skateboards under a tree.
“Don’t jump in yet!” Joel blurted out. “Toss me my coke first!”
Antonio tossed him his coke, however, not being the most coordinated kid, he completely missed and the coke landed in the water a few meters away from Joel.
“Look! It floats!” They both shouted at the same time.
Excited by this new discovery Antonio grabbed his coke and through it into the quarry then jumped in after it. As his head resurfaced he looked around but could only see one can floating.
“What did you do with the other coke?” He questioned Joel.
“Nothing, it sank!”
They both swam over to the floating can in confusion.
“This one is yours anyways Antonio, its the diet coke.” Joel stated as he slapped Antonio across the head. “Why did my coke sink and your coke floated? They are exactly the same!” Joel was angry now.
“But they weren’t the same, mine was diet and yours was a regular coke. Come on, you can share mine, we better get to school.”
They quickly got dressed and rushed off to school. Joel gave Antonio a punch on the shoulder. “Thanks for throwing my coke to the bottom of the quarry you jerk! You owe me one!”
“I don’t understand why that happened? Why would one can float and the other sinks? Let’s go ask Mr. Powers.” Antonio suggested.
They walked into their science class and explained to Mr. Powers what had happened.
Perform the demonstration as described above. Ask the students for predictions on what will happen with the diet coke and with the regular coke when dropped into the container of water. This demonstration can be performed in front of the class during the reading of the story as well.
Mr. Powers explained to the boys that when an object is placed in water it will displace, or push aside, a certain amount of water. If the object displaces more than its own weight in water it will float. A regular coke can is heavier because of the amount of sugar that it contains. Therefore, the regular can of coke will sink because the amount of water it displaces is less than its own weight, unlike the diet coke that displaces more than its weight in water. He explained how the density of an object is what determines how it will react in water. Density is the mass per unit of volume. The density of an object determines how much liquid it will displace.
Draw a picture of this discrepant event below
Explain why the diet coke floats and the regular coke sinks when placed in water?
Antonio and Joel realized now why their regular coke can floated to the bottom of the quarry while the diet coke can floated. They wondered though if the diet coke and regular coke would perform the same way if placed in a different liquid. Furthermore, they wanted to know if different brands of coke or different types of pop would have the same result as coke.
Develop a plan on how to investigate these questions that the boys have raised.
Would a different type of liquid produce the same results as the water did? Furthermore, would different types of pops have the same type of results as the coke did?
What will I change? What will I keep the same? What/how will I measure?
Record your outcomes in the following chart:
What can you conclude based on your findings?
Complete the story based on what you have learned from this investigation:
How do you feel about drinking regular coke now, knowing that it contains something (sugar perhaps) that makes it much denser than diet coke? Does it make you think about any health concerns?
Can you think of any other examples of food or drink products that have diet and regular options that might react similar to coke and diet coke? Perhaps other types of pop?
Explain what density is and how it plays a role in this experiment?
Draw a picture of what the inside of the two different cans look like and use words to explain why one can floated and the other one sank.
Do you think that coca cola does a good job explaining the difference between diet coke and regular coke on their labels?