Comeback Can

Contributed by: Cory Telfer

Rolling Can

…an activity that’ll keep coming back to you

Big Idea: 

  • Structures and mechanisms throughout our environment have forces that act on and within them

Grade 5: Matter and Energy

Inquiry Skills Used

This is a technological problem-solving activity that involves critical thinking, analyzing, and interpreting skills.

Safety Considerations

You may want adult volunteers to punch the holes in the can ahead of time. Remove sharp edges of the can with a file.


First, discuss with the students some essential energy concepts. For example, energy never disappears; it only changes forms. A car’s fuel source is a form of chemical energy. When the car moves, the chemical energy is transformed into kinetic energy. Ask students to think of other examples of energy transformations. Energy can neither be created nor destroyed. If we could add up the energy in the world, it would always remain the same. It can, however, be stored. Discuss ways this occurs, such as in batteries or in food. In this activity, the concepts of energy transformation and storage will be explored.

What You Need

  • String
  • Coffee can with plastic lid
  • Elastics
  • Weight (large nuts and/or washers)
  • Hammer and nail (for preparation)

What to Do

  1. Use the hammer and nail to make two holes close together near the centre of the bottom of the can and near the centre of the plastic lid.
  2. Push elastic in one hole and out the other (for each pair of holes) so that the ends of the elastic are sticking out towards the inside of the can.
  3. Loop one loose end of the elastic through the other loose end and pull tight (repeat for the second elastic).
  4. Next, attach the weight to these elastic ends using string (or more elastic).
  5. Snap the lid on the can.
  6. Avoid breaking the elastic by not stretching the elastic too tightly in the can.
  7. Ask students to predict how the can will move.
  8. Then, have them roll it away on a flat surface (hallway works well) and observe. Have them consider:

1) What makes the can move the way it does?

2) How will changing the weight affect the way it moves?

3) Where does the energy come from and where is it stored?

Where to Go from Here?

Students could design a project that requires storage of energy, such as a car that moves.  As an alternative way of presenting this, you could prepare one of these cans as a teacher demonstration.  Cover over the ends where the elastic shows with construction paper or stickers and challenge the class to figure out how it works.  Then have the kids build their own.

STSE Links

Energy can be stored in many different ways. Have students identify the parts of the chain of energy conversions from the sun to the can moving backwards. The stored energy theme is often used in movies for slapstick humour purposes. This could be a good opportunity to watch any of the “Home Alone” movies, where energy is stored in contraptions and released as needed to protect him from the hapless burglars.

Cross Curricular Connections


  • Have students describe through a poster or procedure, an energy conversion from one of the “Home Alone” movies.
  • Have students identify stored potential energy by making a list of ways to store various kinds of energy (elastic, chemical, nuclear, gravitational, electrical, mechanical…).

Credit Where Credit is Due

Adapted from ideas in Susan Bosak’s Science Is Scholastic 1991 and Science and Technology: Conservation of Energy Pearson Education Canada 2000.