Lesson Plan: T-GEM and Density

Science 3


Students will be able to identify the reason why an object sinks, floats, or remains neutrally bouyant.

Students will recognize that objects do not sink or float due to their weight/mass but rather as a result of their density.


Computer lab or cart



  • Assess prior knowledge by asking students what types of objects sink or float
  • Ask students to come up with a rule regarding whether an object sinks or floats
  • Have the class log on to the computers and navigate to https://phet.colorado.edu/sims/density-and-buoyancy/density_en.html
  • Have students begin on the blocks of the same mass activity and record which colours sink or float
  • Ask students if this agrees with their rules. If not, what else might explain why some blocks sink and others do not
  • Next have the students complete the same process for blocks of the same size, record their results, and see if they agree with their new rule.
  • Have students open the custom block option and attempt to three different materials to float in the middle of the water. What do their 3 floating objects all have in common?
  • As a class, come up with a new rule to explain bouyancy as a result of an object having the same density as the fluid in which it is sitting.
  • Explain the terms positive, neutral, and negative bouyancy
  • Model calculating denstiy by dividing mass by volume. Grade 3’s will likely need calculators
  • Return to the simulaitons and have the students students check this new theory using the blocks of same density setting.
  • Extension: have students use the mystery blocks option, the demonstrated calcuation, and the density reference chart in the simulaiton to discover the identity of each of the mystery blocks.



  1. Hi Daniel,

    The concept of density and buoyancy seems to be perfect to explore using a PhET simulation because it ensures all students are visualizing that same information; there is no ambiguity. In real lab experiments, because of the confounding factors (i.e. water level and temperature, etc.), it can lead to different results for students, which may create more misconceptions!

  2. Hi Daniel,
    I was wondering if this was an introduction to your buoyancy unit or where it fit into the unit. Would you expect the students to know the vocabulary ahead of time, like the difference between mass, weight and density? Would you have the students discover these definitions on their own or would you provide them with an explanation? I know my students always get confused between mass, weight and density so I wondered if you had a good tip on how you deal with it with your students?

    Would you only use the simulation or would you try an in class component?
    Like Gloria, I think the phet simulation for buoyancy is a great choice for this grade level as it has everyone on the same playing field.

    1. Hi Catherine,

      Yup, looks like I missed that in my plan. My 6’s know it but I had to teach these terms to them so I an only assume the 3’s would not know them at all. I think I would use more of an emergent approuch to allow them to ask the question or prompt them to ask. For instance, I might ammend the process to include:

      – Once the simulation is open to the “objects of the same mass” page, ask the students to look for any unfamiliar terms.
      – If they notice mass, provide an introduction on mass
      – If mass is not noted by the students, ask for volunteers to explain it and remediate any noted misconcpetions. Give a summary/full explaination of mass

      I would use a similar process for voume and density with students hopefully realizing that they will need to explain the terms and shift from reactive explainations to pro-active questioning.

      – Dan

  3. Hi Daniel,

    I really liked the flow of your lesson, and the hypothesizing and re-evaluating that you are having the students engage in. I had not focused on the science 3 header at the top, so I was actually quite surprised when I got near the bottom and read that grade 3’s would need calculators. Because of the grade level, I wonder how in-depth you would make the data collection? Would you ask students to visually represent the data somehow after they had finished collecting it, or would you be satisfied that they had “dipped their toes” into the process of data collection at this grade level? I also wonder, as Catherine touched on above, whether you would have students complete a more “traditional” science lab on this assignment as well, or would you stick to the PhET simulation?
    Thank you for sharing!

  4. Great questions class for Daniel’s lesson sketch. There are a number of concepts in science at play in this lesson. Which curriculum is it for and how long do you envision it? I like how you ask at various points for students to continuously explain what they find using the simulation. This is an interactive way to encourage students to think out loud for causal mechanisms and associations that undergird their observations. It sounds like you are following one of the learning cycles, since there is a process of hypothesizing and re-evaluating a rule that gets established by the class. For this, headers might help to delineate which phase of the cycle the teacher and students are in. Also, it would be great to imagine how one might scaffold different rules or explanations that emerge among the group for this step (or others like it): As a class, come up with a new rule to explain bouyancy as a result of an object having the same density as the fluid in which it is sitting. This lesson has students return to the simulation in a very thoughtful and interactive way. Thank you for sharing this simulation and this topic for grade 3s. Samia

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