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).
- Generate – students use a set of data or computer simulations to hypothesize relationships in the analyzed data.
- Evaluate – students use the identified relationships and test them out on a new case or example.
- 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
- 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.
- 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.
- 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.
- 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.