Introduction

This task was inspired by a common introductory physics exercise and by a theoretical consideration presented during a workshop at the GIREP Conference in Jyväskylä in 2011. The primary goal is to explore buoyancy and density through both theoretical calculation and hands-on experimentation. Surprisingly, the experiment disproved theoretical predictions, providing an excellent platform for open inquiry. The focus of this task is on the theoretical considerations involved in calculating the position of an ice cube in a liquid column, an experiment that tests the theoretical prediction, and an inquiry into why the two are not similar. Therefore, the aim of this task is to introduce students to both aspects: theoretical prediction and experimental testing.

The task emphasises upholding the idea that “an experiment is always right.” Theoretical predictions, which serve as the starting point, may not always match experimental results. These predictions can be incorrect or miss certain factors. To fully understand the experiment, it is often necessary to revisit the entire setup, ask multiple questions, and explore different phenomena that might or might not influence the outcome. If, after this process, a plausible explanation consistent with the experimental results is found, it is likely to be correct. Therefore, this activity primarily aims to develop skills in experimentation, questioning, and drawing conclusions.

For the task to be effective, students should initially understand the concepts of density and buoyancy. They need to be familiar with the definition of density and how density is calculated from measured quantities. They should also understand the expression used to calculate an object’s buoyancy. From a mathematical perspective, students must be able to manipulate simple algebraic expressions and comprehend the meaning of the results they obtain.

Task Description

This task transitions from theoretical prediction to experimental verification, aiming to bridge the gap between expectations and reality. Unexpected experimental outcomes prompt a deeper investigation into the physical phenomena involved, including density, buoyancy, surface tension, and hydrophobic interactions.

The question is simple, so is the experiment: An ice cube is floating in a glass of water. What happens with the ice cube if the oil with a density lower than the density of ice is poured into the glass?

Two main theoretical predictions are considered:

•         The ice will sink deeper into the water due to the additional pressure from the oil.

•         The ice will float higher or even into the oil, as both water and oil contribute to buoyancy.

A simple experiment shows that the behaviour of the ice cube is far from predicted. The analysis of behaviour shows that it is not straightforward to establish conditions in which the simple calculated prediction holds. However, during the process, one can easily develop the activity into a serious and interesting open inquiry that connects physics, mathematics, and chemistry. The introductory section of the task includes exercises in mathematics and physics. The middle section involves structured inquiry-based learning, while the final section features guided inquiry-based learning.