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Daily Do

Why Does The Can Come Back?

Disciplinary Core Ideas Is Lesson Plan NGSS Phenomena Physical Science Science and Engineering Practices Three-Dimensional Learning Middle School Grades 6-8 Grades 9-12

Sensemaking Checklist

Welcome to NSTA's Daily Do

Teachers and families across the country are facing a new reality of providing opportunities for students to do science through distance and home learning. The Daily Do is one of the ways NSTA is supporting teachers and families with this endeavor. Each weekday, NSTA will share a sensemaking task teachers and families can use to engage their students in authentic, relevant science learning. We encourage families to make time for family science learning (science is a social process!) and are dedicated to helping students and their families find balance between learning science and the day-to-day responsibilities they have to stay healthy and safe.

Interested in learning about other ways NSTA is supporting teachers and families? Visit the NSTA homepage.

What is sensemaking?

Sensemaking is actively trying to figure out how the world works (science) or how to design solutions to problems (engineering). Students do science and engineering through the science and engineering practices. Engaging in these practices necessitates students be part of a learning community to be able to share ideas, evaluate competing ideas, give and receive critique, and reach consensus. Whether this community of learners is made up of classmates or family members, students and adults build and refine science and engineering knowledge together.


In today's task, Why does the can come back?, students experience the phenomenon of the comeback can - a can that when sent rolling along a level, horizontal surface, eventually changes direction and rolls back to the sender. Using the practice of developing and using models and the thinking tools of patterns and cause and effect, students begin to develop an understanding of the relationship between forces and energy.

This task requires at least one "comeback can" constructed ahead of time (see directions and tips below). If you are in a face-to-face setting, consider building at least one comeback can per each group of four students. Students should NOT be part of the construction process.

Build Comeback Can(s)

.Materials (per comeback can)

  • empty can with lid (Quaker Oats, coffee, and paint cans work well)
  • large rubber band
  • *hex nut
  • two paper clips
  • scissors
  • pen or screwdriver (to punch holes in bottom and top of can)
  • masking tape


  1. Use the pen to poke a small hole in the center of the bottom of the can. Then poke a small hole in the center of the lid. Set aside.
  2. Cut the rubber band so it is in one long strip.
  3. Slide the hex nut onto the rubber band strip and then tie the rubber band back into a loop.
  4. Use the pen to push the rubber band through the hole in the bottom of the can. Slide a paper clip through the rubber band to keep it from being pulled back into the can.
  5. Stretch the rubber band and use the pen to push it through the hole in the can's lid. Slide the remaining paper clip through the rubber band to hold the rubber band in place.
  6. Cover both paper clips with masking tape to conceal the rubber band.

*You can substitute a fishing sinker or washers for the hex nut. Make sure whatever you're using for as the weight does not touch the side of the can when suspended on the rubber band.

Watch the Come Back Can - Kids Craft Toy video to support the directions above. If you don't have a hex nut available, watch the Rollback Can Experiment video to find out how to use a 9-volt battery instead.

Give your comeback can a little push. Does it roll back to you? If the answer is yes, you're ready to begin!

Experience the Phenomenon

Tell students you have a puzzling phenomenon to share. Ask them to first create an I See - I Think - I Wonder table to record observations, ideas and questions.

Place the comeback can on the floor or long desk and roll it away from you. Each time the can returns, push it away from you using the same amount of force each time. Don't let the can continue to roll back and forth on it's own at this time.

Ask students to turn to a partner and share their observations. As you move around the room, listen for students to share ideas about forces and energy. Bring students back together and ask them to share an observation or their partner's observation with the class. Create a class list of observations; make sure the list is easily accessible by all students. If students share questions, ask them to make sure to record that question in the I Wonder column of their table.

Share with students, "I hear many of you sharing ideas about forces and energy. Do you think we can use ideas about forces and energy to explain why the can comes back?"

Assign students partners. Then assign each pair of students one of the following tasks:

  • Create a model to explain why the can rolls away and then back to you using ideas about forces, not energy. We're only interested in the forces acting on the can to help explain it's motion.
  • Create a model to explain why the can rolls away and then back to you using ideas about energy, not forces.

Make sure the same number of student pairs are working on each task.

As you move around the room, you might ask the students working on the forces models:

  • I see you're representing a force here (point) on the can. What is pushing/pulling on the can? (What is doing the pushing/pulling on the can?)
  • How are you representing forces?
  • How are you representing the direction/size of the force?
  • When are the forces acting on the can balanced/unbalanced? How could you show that forces are balanced/unbalanced on your model?

You might ask students who are working on the energy models:

  • How are you representing energy on the model?
  • How are you representing the transfer of energy on the model?
  • How are you representing different amounts of energy?
  • I see you're representing energy like this (point) here, and like this (point) here. Why?
  • How might you represent transformation(s) of energy on the model?

Next, create small groups of four students by combining a pair of "force" students with a pair of "energy" students. Ask the groups to work together to create a consensus model that uses both force and energy ideas to explain why the can rolls away and then back to you.

Make Predictions

Roll the comeback can across the floor or table using the same amount of force as you did before. Say to the students, "Without making changes to the comeback can itself, what variables could we change?" Ask students to independently think about the variables and then record their ideas. Then, ask students to share their ideas with their small group.

Bring the students back together and ask them to share variables their group identified. Students might share these variables:

  • the amount of force applied to the can
  • where (location on can) the force is applied
  • the surface (texture) the can rolls over
  • the amount of time the force is applied
  • how the force is applied
  • length of time/cumulative distance can rolls between pushes

Say to students, "Let's test how well our models can predict how changing a variable will effect the way the comeback can rolls." Ask students to identify three variables they want to change and tell how each change will affect the comeback can's motion based on their model (use the model as the basis for evidence). Give students independent thinking time to complete this task; consider asking students to use the If-then-because sentence stem (scaffold) for each prediction.

Ask students to return to their small groups and share their predictions. Then ask groups to choose three predictions to test. They can change the same variable in three different ways or choose three different variable to change. Create a space for groups to post their predictions.

If you have multiple comeback cans, provide each group with a can to test their predictions. If you only have one comeback can, categorize the groups' predictions (or ask students to categorize the predictions) and then test each set of predictions. Ask students to make and record observations and note any new questions that arise in their I See-I Think-I Wonder table (and answer questions they now can).

Ask student groups to share their predictions and the outcome of the tests (related to their predictions) with the class. You might have them post the test results next to their predictions. Next, ask student groups to look for patterns in the class data. Bring the class back together and ask groups to share patterns they observed. Create a class record of the patterns the groups identify.

Revise Models

Give student groups time to add to and/or change their group consensus models based on the data collected during testing and the patterns identified by the class. Then, ask groups to post their models around the room or in a shared virtual space. Instruct groups to visit at least two other group models and at each one observe and record:

  • two similarities between their model and the other group's model
  • one difference between their model and the other group's model

Allow students time to return to their group consensus models and make revisions. As you walk around the room, ask student groups why they are adding to/changing their models. You might ask, "How does this addition/change help to explain why _____ caused the comeback can to _____?"

Bring students back together. Create a list labeled, "Must-Haves" and ask students to share what they think must be included on a model that explains why the can rolls away and then comes back to you. Students will likely include:

  • a force that starts the can rolling
  • a force that stops the can
  • a force that causes the can to change direction
  • motion energy transferred from the arm/hand to the can
  • motion energy of the can
  • energy stored in the can
  • stored energy transformed to motion energy (and vice versa)
  • motion energy transferred to the air/floor (sound, heat)

Consider writing each "must-have" on a paper strip or digital sticky note. Task students to work with a partner or small group to connect statements about forces to statements about energy. For example, students might connect "a force that starts the can rolling" with "motion energy transferred from arm/hand to can". Ask groups to share the connections, and physically move the statements on the class "must-have" list to reflect the connections. If the same statement is needed for more than one connection, write the statement a second time and make the connection. You might ask students if there is pattern in the connections they have made between forces and energy. Students might say statements about forces connect to statements about the energy transfers.

Reveal the inside of the comeback can. Ask students to revisit the questions recorded in the I Wonder column of their table. Which questions can they now answer? What new questions do they have?

NSTA Collection of Resources for Today's Daily Do

NSTA has created a Why does the can come back? collection of resources to support teachers and families using this task. If you're an NSTA member, you can add this collection to your library by clicking Add to My Library (near top of page).

Check Out Previous Daily Dos from NSTA

The NSTA Daily Do is an open educational resource (OER) and can be used by educators and families providing students distance and home science learning. Access the entire collection of NSTA Daily Dos.

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