從力的比較觀點探討九年級學生理解浮力概念困難之研究

Abstract

摘 要 浮力的概念，在物理學當中是屬於重要且不容易學習的單元，學生必須統合之前學過的密度、體積、質量、壓力…等許多相關知識，並且要能掌握阿基米德的原理及物體在液體中抽象的受力情形，才得以架構出完整的浮力概念。鑒於近年來的基本學力測驗，有關浮力問題的答對率普遍偏低，研究者在學生解題過程中發現，普遍學生不太會使用物體在液體中受力比較的情形來解浮力的問題，許多可以用簡單的受力比較來解決的浮力問題，學生卻被其它複雜的想法所困住，反而無法解答。研究者查閱國內外十八篇相關討論浮力的文獻，尚未發現有從受力的比較觀點，來探討物體在液體中所受浮力的情形，因此本研究設計欲探討學生能否從物體受力的比較情形，來減少在浮力方面的學習困難，希望藉此提升學生在學習浮力的整體成效。 本研究主要從「力平衡」的概念為主軸，探討學生在使用物體受力的比較來理解「浮體」浮力、「沉體」浮力、「判斷浮沉」、「液體密度改變後的浮體」浮力、「液體密度改變後的沉體」浮力，這五個面向的浮力問題。本研究的浮力試題經由預試後確定信度、效度皆達到標準後正式施測。 研究結果發現：一、能掌握力平衡概念的學生，在以上有關浮力的五個向度的答對率皆高於未能掌握力平衡的學生。二、整體而言男生在浮力各向度的表現是優於女生的。三、使用「受力比較」模式解浮力題目的答對率高於使用「密度」模式的學生。 綜上所述，使用力的比較方式來解浮力問題可以減少學生在學習浮力的困難，而且可以提高浮力問題的答對率。

Abstract Buoyancy is an important but difficult concept in physics. Students need to integrate knowledge that they have previously acquired about density, volume, mass, and pressure. Moreover ,they need to understand Archimedes' principle and concept of the abstract force on an object in liquid before they can completely frame the concept of buoyancy. In recent years, students also had relatively lower performance in solving problems related to buoyancy in the Basic Competence Test. The researcher found in their problem-solving process that most of them were not familiar with comparing the forces on an object in liquid to solve buoyancy problems. Many problems could be solved through comparison of forces, but students' minds were restrained by other complicated methods and could not solve the problems correctly. In a review of 18 local studies of buoyancy, it was found that none of the existing studies used force comparison to explore the buoyancy of an object in liquid. Thus, the purpose of this study is to investigate whether the learning of buoyancy would be easier for students through comparison of forces on object, so as to enhance the overall learning effectiveness of students’ on buoyancy. Based on the concept of “force equation”, this study probed into the understanding of students on buoyancy from five perspectives, including buoyancy of “a floating object”, buoyancy of “a sinking object”, “judging whether an object is floating or sinking”, buoyancy of “a floating object after liquid density has changed”, and buoyancy of “a sinking object after liquid density has changed”. Before the formal test, a pre-test of the test problems about buoyancy was conducted to ensure validity and reliability of the test instrument. The research findings were: (1) Students familiar with the concept of force equation demonstrated higher correct response rates in all aspect of buoyancy problems than those unfamiliar with the concept of force equilibrium; (2) Generally, boys outperformed girls in all aspect of buoyancy problems; (3) Students who used “force comparison” to solve buoyancy problems also outperformed those who used “density” to solve buoyancy problems. To sum up, using force comparison to solve buoyancy problems could reduce the difficulty of solving buoyancy problems and also enhance the correct response rate.