Volume and Capacity

coffee

My fourth grade students are studying volume and capacity this week. As I introduced the topic earlier in the week I started to observe that students had a minimal understanding of volume. They remembered the l x w x h formula.  They remembered creating cities last year and finding the volume of different rectangular prisms. So I brought out my supply of centimeter cubes and the class built different rectangular prisms. Being able to replicate rectangular prisms with centimeter cubes was a great way to start off the lesson. Students reconnected (as we studied this last year and I kept on reminding them) the concrete and abstract models of rectangular prisms and volume. At this point the class started to explore the volume of different 3d shapes.   We had a few volume estimation drills with objects in the classroom. Students seemed to do well with triangular prism estimation (1/2 of the rectangular prisms) but had trouble with cylinders.   I had students work in groups to estimate the volume of a cylinder in the classroom.

They made their estimates in cubic centimeters. I thought that the centimeter cubes that I had on my desk would help students visualize the volume better. Students were given the formula to find the volume a cylinders but were still quite a bit off with their estimates. The class then calculated the actual volume.  After their first attempt the class started to pinpoint the errors. We made a list:

  • Adding the radius twice instead of multiplying ß most errors fell into this category
  • Using incorrect number for Pi
  • Used the diameter instead of the radius
  • Estimated using incorrect units
  • Rounded the measurement incorrectly

Keeping these errors in mind, our second volume attempts were closer. Not all, but most groups were on the right track and could visualize an approximate volume of the second cylinder. After all the results were collected the students and I measured the exact dimensions of the cylinder. I had a few students look astonished that the cylinder could “hold that many cubes.” They couldn’t believe it and didn’t think it was reasonable. So we went back to a different representation. I put the container under the document camera and we created an approximate layer of cubes on the bottom of the cylinder.

layer

Finding the radius wasn’t used for this demonstration. We added a few more cubes to add for the tiny spaces. The class found the height and used it along with Pi to estimate the volume.

height

That estimate was close to the actual measured amount. I could sense that students were developing more confidence as we moved into the next part of the lesson.  This seemed to make sense to the students. Being able to quickly backtrack to a different representation helped students see volume differently.

The next day students explored the similarities between cubic centimeters and milliliters. This was a challenge for some of the students and some didn’t believe that 1 cm3 was 1 ml. Part of the reason is that students are often used to working with volume and capacity in completely different situations. Liquid and solid measurements are often separated into different lessons and units. Rarely are they combined at the elementary level so this was fairly new to students. While researching a few different options in helping make connections I settled on using an activity that mimics this video.

I passed out the assignment and students were placed in groups.  I modeled how to start the assignment and answered questions.

volumeandcapacity.jpg

 

Students worked in groups and were given options in how to showcase their understanding of cubic centimeters and milliliters. Students filled up their graduated cylinders to specific levels and I added a small bit of food coloring. It’s so funny how fourth graders can get so excited over this. Note to self:  buy extra food coloring.  Students added actual centimeter cubes to the graduated cylinder and watched as the water level rose.

Students reviewed the difference between the water levels after cubes were dropped to the bottom of the graduated cylinder. Students then recorded their explanation to what happened and how cubic centimeters are equivalent to milliliters. We finished up the day with an exit card on volume.

 

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