Balancing the scale with T-GEM

Elementary Science


Topic: Mass


Misconception: That the size and shape of (an) object(s) affects the balance on a scale even if the weight is the same


Students can sometimes get confused between the type of objects you may put on both sides of a scale and its impact on balance.  Some students think that if you put 1 pound of paper clips on one side of a scale and a 1 pound cube, the scale will not balance out.



  • Balance scales
  • Computers
  • Different objects





  • Assess students prior knowledge by asking them when using a balance scale, what is the relationship between the length of the arm and the mass of the objects that balance on it? Do different materials impact the balance of the scale?
  • Ask students to discuss with a partner how they will be able to get the scale to balance using different materials
  • Ask students to come up with a theory for how to get the scale to balance perfectly level
  • Ask students to use different materials to place on each side of the balance to see if smaller less heavy objects on one side and a single heavy object on the other of equal weight will influence the balance scale.
  • Have students hypothesize and test out if adjusting where the object(s) are placed on the scale influences
  • In partners, have the groups come up with some new rules for understanding weight and mass.
  • Have students use the PhET “Balancing Act” to test out different materials and their weight.


This lesson draws upon the T-GEM model.  According to Khan (2007) this model focuses on three important steps: Generate, Evaluate, and Modify.  In this lesson students are asked to generate their own ideas around mass /weight and how different objects will influence the balance of the scale. The students compare their predictions with their partners and then test out their theories that they have come up with.  After testing their hypothesis various times, the students then come up with some scenarios why different objects and lengths of arms will influence the balance scale. This is the ‘evaluate’ portion of the T-GEM.  The last stage of the lesson allows students to modify their original beliefs about weight and mass.  They are able to gain an new understanding regarding the relation of weight and mass to balance.  The extension part of the lesson is meant to give students further time to experiment with the ideas that they toyed with in the lesson. As Stieff et al (2003) discusses, it’s important to give students opportunities to give students virtually unlimited opportunities to experiment with real world objects.  Using visualizations allows students to understand the differences between physical variables and the equilibrium posting (Stieff et al, 2003). Students have the opportunity to test what they’ve learned  about balance and make predictions about how different objects will make the plank balance.




Khan, S. (2007). Model-based inquiries in chemistryScience Education, 91(6), 877-905

Stieff, M., & Wilensky, U. (2003). Connected chemistry – Incorporating interactive simulations into the chemistry classroom. Journal of Science Education and Technology, 12(3), 285-302.


  1. Hi Tyler,

    I like how approachable your plan is for the students. I too used the scale simulation in my lesson, and I particularly liked that students were free to place objects are varying distances from the fulcrum. It’s also nice that the scale in the simulation moves at a speed relative to the difference in forces on either side, which helps students visually observe how close they are to balancing the equation.

    Thanks for the lesson plan.

  2. Hi Tyler,
    I really appreciate the simplicity of your lesson and the simulation lab you can do that will emulate the hands-on work done in class while providing students with another opportunity to see their findings in a slightly different way. It is important for us to provide multiple views to reach a larger variety of learners and learning styles.

  3. Thanks Tyler for examining Mike Stieff’s work to inform your design of the lesson which includes the integration of both non-digital and digital activities/technologies. What might be the affordances of each technology in terms of the phases?

    By making the activity explicit with the phase (subheaders in the plan might also assist), we can see the richness behind the lesson that involves the use of scientific processes such as: making predictions, hypothesizing, comparing, evaluating, testing. We can also get a window into the guiding strategies that will scaffold student understanding such as asking students to “come up with some scenarios why different objects and lengths of arms will influence the balance scale”. Samia

    1. Hi Samia,

      I believe that allowing the students to experiment with different levers and objects will help them grasp the required concepts for the lesson. Providing a virtual environment to experiment allows students to use objects that may not be available at the school to experiment with in a real life environment.

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