Free Falling with T-GEM

Free fall is discussed in the Projectile Motion unit in the Manitoba Grade 12 Physics Curriculum.  Rane (2015) states,”researchers have proved that free fall misconceptions are very common among the students” (p. 1).  Upon a literature review, Rane (2015) has also found that, “most of the students believe that…heavier objects fall faster than lighter ones” (p. 2).  Upon conducting analysis using a 15 item free fall diagnostic test, it was found that “…students [believed] heaver objects…take half the time [while others believed] lighter [objects]…move faster” (p. 6).  It is clear that the concept of free fall is challenging.  I have designed the following T-GEM lesson to assist students in understanding free fall and associated ideas like mass, acceleration, velocity, and velocity-time graphs.

Khan (2007) describes the GEM process as a “…cyclical pattern in which students [generate], [evaluate], and [modify] hypotheses…” (p. 877).

  1. Generate – students use a set of data or computer simulations to hypothesize relationships in the analyzed data.
  2. Evaluate – students use the identified relationships and test them out on a new case or example.
  3. Modify – students modify their original hypotheses and apply them to new cases.

Khan (2007) highlighted an important prerequisite to the GEM cycle.   It is important to have a small but important didactic lesson on introductory and background information that helps students make sense of the data in the first place.  If the students don’t know what they are looking at, seeing relationships in the data becomes difficult.

Free Fall Lesson

  1. Prerequisite Information – students are introduced to the Free Fall Tower gizmo by Explore Learning.  Students are given instruction on how to manipulate the gizmo and the data that can be collected from the gizmo.  They are given a brief review of the concepts of acceleration, velocity, and mass.  Graphs of velocity versus time are also reviewed for cases of acceleration and constant velocity.
  2. Generate – students are asked to determine if there are any relationships as they observe different objects free falling.  They are asked to manipulate their gizmo with air as the atmosphere in this part of the activity.  They are also asked to observe the graph section for trials.  Some objects appear to have constant velocity as they near the end of their fall. – The goal here is to generate a hypothesis that larger objects fall to the ground faster and to generate explanations for this observance.
  3. Evaluate – once students establish the relationship that larger objects fall to the ground faster – the students are asked to conduct similar manipulations, instead now with no air (vacuum) as the atmosphere.  They quickly ought to realize no matter which object combination they choose, all objects appear to fall at the same time, regardless of shape, size, or mass.  This is the discrepant event that will challenge their original hypotheses and force students to come up an adjustment to their original hypothesis.
  4. Modification – Students discuss the discrepant event and attempt to come up with new explanations for why all objects appear to fall at the same time.  Through discussion with the teacher’s guidance – students are helped to the conclusion that mass, size, shape have no impact on free fall as acceleration due to gravity affects all objects equally.  The issue of different objects falling at different times is because of their shape and air resistance when air is the atmosphere chosen.  Students apply their new explanations to in class experiments with real objects to further solidify the concept of free fall.


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

Rane, L. V. (2015). Investigating Student’s Conceptual Understanding of Free Fall Motion and Acceleration Due to Gravity. International Journal of Allied Practice, Research and Review, II(VI), 01-08.


  1. Hi Vibhu,

    Thanks for sharing the simulation on Gizmos! Though I have no familiarity with this physics topic, I can definitely adapt it for a gravity and force unit for my grade 7 students. The misconception that heavier objects fall faster than lighter objects sounds like a common occurrence in many students, but your exploration of teaching it from T-GEM appears very organized and effective!

    1. HI Gloria!
      Yes I have seen this misconception often as well so I thought it would be a good exercise for myself to develop a T-GEM approach to this concept.
      Thanks for sharing!

  2. Hi Vibhu,

    I would be a little hesitant to promote an incorrect initial hypothesis (that larger objects fall faster). My understanding is that the generate phase should not really be prescriptive, only that students should be able to provide some kind of explaination.

    One thing that I ran into with astronomy misconceptions is that both myself and my students have moments of doubting the simulations. Being able to supplement with real life example/demos to illustrate the impact of air resistance and videos from vacuum chambers may help with this. I think there was a NASA video floating around a while ago of a bowling ball and a feather dropped in a vacuum chamber and them falling at the same rate.

    – Dan

    1. Hi Dan!
      It would definitely be helpful to use live demonstrations or video demonstrations on the differences in free fall both in the presence of air and its absence. As far as hypotheses are concerned, in the true spirit of the scientific process, I think it is okay to make hypotheses (based on simulations in the presence of air) that may in fact be proven wrong upon analysis of new data (based on simulations in the absence of air). It would be a humbling lesson for students that not all ideas or explanations are right from the get go and that upon further experimentation hypotheses can be proven equally right or wrong.

      That being said, you are right. One explanation or another shouldn’t be pushed by the teacher during the generate stage, nor should I suppose the teacher should correct the explanations students offer in this initial stage.

      Thank you for sharing!

  3. There is a nice discussion emerging here on at least two related issues on teaching math or science with technology: a) how long do we let students keep their misconception before “correcting” them? and b) are simulations for learning math or science real and should we trust their findings? For a) The teacher in the study on GEM referred to his approach as guided discovery rather than more prescriptive methods of teaching classroom chemistry (such as, demonstrate a problem, provide sample problems, supply time to solve problem sets). Perhaps we can say in the generation phase that from experience, students are likely to offer a set of hypotheses (in the case on free-falling, that larger objects fall faster because they are heavier)? In the research on GEM, there can be several groupings or types of hypotheses offered to explain the same finding by students. In this case, the teacher attempted to work through a few of them with Evaluate-Modify cycles while others he worked out at the same time or took a vote on which ones to pursue. On average over 52 science topics, each T-GEM took 20 minutes, yet the teacher did not correct students per se nor encourage them to read the text before the lesson, speaking to Vibhu’s point on not all explanations are right. The T-GEM method would suggest that like Heather in the Private Universe, there is some advantage to students’ grappling with their misconceptions and experiencing dissonance rather than being told the correct answer from the outset. The second issue raised is about using simulations themselves for teaching science or math. In the case of Chemland, the simulations represent a larger data set and aim to help users learn conceptual relationships (versus a virtual lab type of simulation). It might be important for teachers to discuss how a data point was produced in the dynamically generated graphs on black-box simulations like PhET, Gizmos, and others. Simulations, virtual labs, labs, and demonstration each will have their cognitive affordances for learning and can support one another in an integrated learning experience. Thank you Vibhu for the free-fall GEM cycle and the two Gizmo simulations that are thoughtfully sequenced to promote dissonance and learning. Samia

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