Perceived effect on buoyancy of weight vs. gravitational force

Abstract

As part of a larger investigation into students' conceptions about buoyancy, we investigated the prevalence of the belief that the gravitational force on an object changes when the object is placed in a fluid. We also investigated the effect of describing the force as "weight" instead of "gravitational force." During the first phase of the study (Winter 2016 to Fall 2016), students at two different institutions were asked to identify the correct free-body diagram (FBD) for a ball floating in water, and then for the same ball held down while fully submerged under water. Half of the students were shown FBDs involving "weight," and the other half were shown FBDs involving the "gravitational force." During the second phase of the study (Fall 2017 to Spring 2019), students at one of the institutions were asked to explicitly compare the strength of either the weight or the gravitational force on the ball when it was falling, floating, and held submerged. This paper will report on the fraction of students who indicated that the weight or gravitational force differed between the scenarios and will discuss the effects of both the question asked and the wording used to describe the force.