For Good Measure

Contributed by: Derek TottenBoy and bag

…a good balance of science and fun!

Big Ideas: 

  •  Simple machines help objects to move.
  • Simple machines and mechanisms make life easier and/or more enjoyable for humans.

Curriculum Connection: Grade 3: Structures and Mechanisms

Inquiry Skills Used

This is a research activity where students will explore how a mechanism can be adjusted to make movement easier.

Safety Considerations

Students should be reminded not to overload the mass in the bag as the metre stick could break and subsequent injury may then occur.  Remind students not to place their feet under the load on the metre stick.


This activity involves student discovery of the various ways to strengthen materials as well as an introduction to simple levers.  A metre stick serves as an introduction to both of these concepts in a simple, yet effective investigation.

What You Need

  • Metre sticks
  • Plastic grocery bags with some mass (blocks or books) inside it
  • Large paper clips
  • Fulcrum (a piece of doweling or a tin can work well)

What to Do

  1. Ahead of time, drill a hole in one end of the metre sticks (large enough to hook a paper clip through).  Introduce the metre sticks to the class and invite student pairs to hold the metre sticks between themselves.  Explain that normally you use the metre stick to measure lines, but today you will be measuring strength and force.
  2. Have the students choose a classroom object (e.g., book) and, with your approval, balance it on the metre stick between them.  Were some objects easier to balance?  Why?  Did the manner in which they held the metre stick make a difference? Could they balance more than one object on the metre stick at a time?
  3. Give each group a plastic grocery bag and have them insert the metre stick through the handles of the bag, placing the bag in the middle of the metre stick.  The metre stick should be held in their hands exactly as it was earlier in the lesson (markings towards the floor and ceiling).
  4. Have each group place an item into the bag then lift the bag off the floor.  Supporting an object should be much easier with the aid of the bag.  Have students observe their metre sticks, noting the sag in the middle.  Add another item to see the sag become more evident.
  5. Have the students twist the metre stick in their hands so that the markings are now facing the walls.  What did they notice?  If any of them have unfinished basements at home, ask them to recall the wooden supports in the rafters (ceiling). How do they look?  Why are they placed this way (flat or its edge)?
  6. Now introduce the challenge of lifting the bag with only one person. This should be done as though they are holding a fishing rod.
  7. Next, help them to set up a first class lever with the fulcrum placed in the middle of the metre stick. Attach a paper clip (like a hook) through the hole in the end of the metre stick to allow the bag to be easily attached.  Having the bag hanging over the edge of a desk or table also works well.  Have the students try lifting the load by pushing down on their end of the metre stick (lever).  They should try different fulcrum locations until they can make some generalizations.
  8. Does adjusting the fulcrum affect the distance that the lever moves? Students can record their experience in a picture or diagram.

Where to Go from Here?

Introduce students to 2nd and 3rd class levers.  Take the class outside to the teeter totter as a performance task.  They can use what they know about levers and balance to carefully place an uneven amount of children on a single teeter totter and balance it.

STSE Links

Does adjusting the fulcrum affect the distance that the lever moves?

Explore how humankind has used this technology to create work saving devices.

Cross Curricular Connections

Language Arts

  • Have the students write a story about how a group of children found a buried treasure in the school yard by moving a huge boulder using a simple lever.

Visual Arts

  • This activity also incorporates visual arts when producing a three-dimensional work of art that communicates a specific idea.