國三學生在浮力情境中對作用力辨識與力平衡理解之探討

Abstract

本研究的主要目的是探討國三學生，在處理需要力平衡概念的浮力問題時，是否能根據物體在液體中不同的浮沉情況，辨識出作用於物體上所有的作用力？以及探討學生是否能利用力平衡的觀點，來判斷在不同的浮沉情境，液體中物體所受作用力之間的關係？ 研究對象為桃園縣某國中3年級的學生105名，利用研究者自行編製的「浮力情境紙筆測驗」為研究工具，包含繪製力圖、作用力的辨識、浮力與重力的關係判斷。調查國三學生在浮力的問題情境中，其具備的力學概念。另一方面，為了進一步了解學生對於力的理解，以及力平衡觀念的認知，則針對18位學生利用半結構的訪談加以詮釋分析，以期能探究學生的力學概念和了解學生浮力單元的學習困難。研究結果如下： 1.物體所受作用力較少時，學生在繪製力圖及辨識作用力的表現較好。 2.學生在繪製力圖時，通常能辨識出物體所受的重力與浮力，但容易忽略其他的作用力。 3.部份學生在繪製力圖時，誤將壓力視為一種作用力。 4.學生在使用浮力公式時，通常只注意其中一個因素，而無法同時考量物體體積與液體密度的變化，造成判斷上的錯誤。 5.部份學生以直觀方式判斷浮力，認為浮力越大，物體越容易上升；浮力越小，物體則容易下沉。 6.部份學生無法瞭解浮力的成因，以至於認為物體在液體中的位置，會改變物體所受的浮力。 7.部份學生缺乏辨識浮體與沉體的能力。This dissertation aims to explore if junior high school students (ninth grade) could identify all the acting forces exerted on a floating object in different circumstances when they deal with buoyancy problems. In addition, this thesis also studied whether students could distinguish the relationship between all the acting forces in different circumstances based on the concept of equilibrium.

Our research sample involved 105 junior high school students in Taoyuan County, Taiwan. A test written by the author was exploited as an investigation tool which focuses on the identification of applied forces, force diagrams drawing, as well as the determination of the relationship between buoyancy and gravity on the objects being studied. This test would reveal their conception while they worked on the buoyancy problems. On the other hand, in order to fully understand what extent students could reach with respect to the concepts of “exerted forces” and “equilibrium of forces”, interviews with 18 students via half-structure protocol were also pursued and interpreted. The results are expected to help understand their comprehension as well as the difficulties they may have in learning the concept of buoyancy. The findings are summarized as follows:

1.When fewer forces were exerted on an object, the better force diagrams were drawn and the forces better identified. 2.In drawing force diagrams, some students tend to identify the force of buoyancy and gravity easily while neglecting forces. 3.Some students mistook pressure as an acting force. 4.When students used buoyancy equation to resolve problems, they could not simultaneously consider the variation between object volume and liquid density, but rather focus on one quantity, thereby leading to some misjudgments. 5.Some students judged buoyancy intuitively: the larger the buoyancy force is, the easier the object would rise; the smaller the buoyancy force, the easier the object would sink. 6.Some students could not understand the real cause of buoyancy, leading to the misunderstanding that the buoyancy force would differ while an object is differently positioned in a liquid. 7.Some students are not able to differentiate between floating and sunken bodies.