Several times a year my students take part in STEM Challenges. During these daylong endeavors, my third graders work in collaborative teams combining scientific principles with technology, engineering, and math in order to solve a problem or answer a question that’s been posed. While prepping for these challenges can sometimes take quite a bit of effort on my part, the end result is what makes my teacher’s heart soar. I am rewarded with students completely engaged in critical thinking activities that result in audible aha moments through the course of the day coupled with a deep understanding of new concepts. This week I’m excited to share my latest challenge: learning about density and buoyancy using candy — perfect for this time of year when snack-sized candies are plentiful in many houses.
For this activity, my students took part in a sink and float demonstration using candy, then faced the STEM challenge of devising a way to reverse the original experiment's results. Would my third graders be able to make floating candies sink and sinking candies float? The challenge was on!!
In order to build background knowledge for my students (and to save on the amount of candy being used), I conducted the first sink and float experiment for students to observe. To begin, I laid out a large selection of wrapped candies on a table in front of the class. As you can imagine, just seeing all that candy captures their attention; curiosity was piqued and questions begin to fly.
With the students in a circle on the carpet, we passed around the candies for students to get an idea of how heavy each piece was along with its shape.
Next, I unwrapped the candies and asked the students to describe the properties of each one: rectangle, bumpy, crispy, flat, chewy, etc.
At this point, I handed out the paper below and asked students to predict if they thought the eight candies I’d preselected would sink or float in a cup of water.
Click on the image above to download and print a customizable document.
I tallied up the class responses and students recorded them on their data charts. Within their groups students discussed why they believed certain candies would sink or float.
Students had research time to find out what each candy was made of and to look up key words that appeared on the candy wrappers such as nougat and whipped filling.
Clear plastic cup filled with 8 oz. of water
Paper towels to absorb water when candy is removed
One by one, I dropped the unwrapped candies into a clear plastic cup filled with 8 oz. of water. Students recorded whether each candy sank or floated and made written observations. For example, in their observations they noticed that all the candies that sank did not arrive at the bottom of the cup in the same manner or at the same speed. Some, such as the solid chocolate Hershey, sank straight to the bottom quickly, while the Twix slowly settled instead.
Students recorded the experiment on their iPads in order to create a Keynote presentation at a later date.
After students observed the candies sinking or floating, we debriefed on why each candy had the outcome it did. Students had figured out that candies that had air pockets throughout, such as Kit Kat, 3 Musketeers, and Whoppers would float while others comprised of dense materials like caramel, solid chocolate or gelatin-based candies did not.
Afterwards, students used their iPads to look up the ingredient labels for the candies we tested to see if they could find patterns. (What they discovered is candy has a lot of sugar in it!) They also wrote down any remaining questions that they had such as what if we left the candy wrapped or what if we flattened the gummy out?
Through observation, the students grasped that candies that are dense will sink to the bottom of the cup. The density of the candy, however, depends on what is inside the candy. Candies that have whipped ingredients like nougat, marshmallow, or malted milk will float because their air pockets make them less dense and therefore more buoyant. Candy that is solid chocolate or filled with peanut butter or caramel will sink because they are denser than the water into which they are dropped.
After students had watched several candies sink or float in a cup of water they were challenged to design their own test that would have results that were opposite of those we observed.
Working with their teams, students looked through their what if questions and decided how they could test their questions.
Time was provided for the teams to design their experiment using the downloadable sheet below. Students recorded their underlying question, hypothesis, and materials needed.
Each group went before the class and explained what they hoped to accomplish. Next, they conducted their experiment for the class to see. Standing in front of their classmates, each team explained what they had done in an attempt to reverse the test results. They also explained what scientific principles made them believe their test would be successful.
Some questions my class wanted answered:
Will cutting a 3 Musketeers in half allow the air pockets to fill with water and sink the candy?
Will keeping a candy in its wrapper trap enough air in between the candy and the wrapper to make the candy float?
Will a gummie float if we poke a hole through the center then cover it with tape to trap the air in the center?
Will putting a malted milk ball in hot water cause the protective chocolate coating to melt allowing the air inside the candy to fill with water and sink?
Will using ice water cause the water to become so dense that the candy floats?
After all of our tests were conducted, we discussed and debriefed the results. Students expressed their thoughts in a chalk talk, a way for all student voices to be heard.
When students left that day, many were discussing different experiments they wanted to try at home using candy.
Tip: This is a great activity to do after Halloween when you can ask students to bring in a piece or two of snack-sized candy that can be used in the demonstration.
For another engaging STEM activity try my Valentine Catapult Challenge. It can easily be adapted to fall by using candy corn or small candy pumpkins.