全國中小學科展

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物理與天文學

Wetting Tracing Paper—Fiber Porous Media Curling Behavior and Mechanisms

This research presents a novel approach to understanding the curling and uncurling behavior of tracing paper when exposed to water, identifying limitations in traditional diffusion-based models like Fick’s second law. While Fick's model adequately represents the uncurling phase, where water content is stable, it falls short during the curling phase due to its inability to account for dynamic changes in diffusivity. Our study identifies capillary action, modeled through Richards' equation, as the primary mechanism in the curling phase, where diffusivity varies with water content due to capillary-driven water movement through the paper's porous structure. Experimental data align well with the Richards' equation model, highlighting a saturation point where curvature peaks, governed by evaporation's impact on moisture balance. To simulate this phenomenon, we developed a finite difference approximation scheme based on Richards' equation, discretizing the spatial domain for detailed control over moisture dynamics and incorporating the Robin boundary condition with virtual points. This approach, combined with evaporation considerations, produces simulation results consistent with observed data, emphasizing evaporation’s role in steady-state moisture gradients and the subsequent deformation mechanics. Our findings further reveal that factors like paper thickness, temperature, and salt concentration significantly influence curling behavior. We established linear correlations between peak time and thickness reciprocal, as well as between peak curvature and thickness squared, supporting theoretical models. Temperature affects both peak curvature and curling rate due to changes in viscosity and surface tension, and higher temperatures prevent full uncurling due to sustained evaporation effects. Increased salt concentration heightens peak curvature without altering expansion ratio, suggesting additional variables in play.

懸掛液滴的光學成像性質與其組合應用探討

眾所周知,水滴是生活周遭容易取得且可以放大物的透鏡,藉由作品中的實驗裝置能夠方便的觀察液滴中的成像,且能夠隨意地改變取率半徑和折射率,並搭配手機方便觀察與紀錄結果。若欲知液滴中成像的放大率,可利用測得的曲率半徑帶入「造鏡者公式」得知水滴的焦距,得知焦距後,便可將其帶入「薄透鏡公式」即可得知放大率 (距離水滴的長度不同,有不同的放大率),再利用實驗驗證算出的焦距和放大率是否符合實際的焦距。之後改變液滴的曲率半徑和種類並比較其對放大率的影響 (本研究討論曲率半徑0.1公分和0.15公分的差距、水和食鹽水的折射率差距)。此外,更加以研究「球透鏡公式」與「薄透鏡公式」所算出的數據之差距與實驗觀察結果比較,並應用於複合透鏡中。

磁星短x射線爆發特徵分析:以1E2259+586為例

我們是探討磁星的短X射線爆發(Short X-ray burst)。利用RXTE太空望遠鏡觀測磁星1E2259+586的數據,經由Bayesian block方法對光變曲線篩選找出爆發,並配合「波松分佈」與「虛無假設」找出50筆爆發事件(爆發的正確性有5σ的信心水準)。再利用HDBSCAN非監督式學習演算法來對短X射線爆發進行分群,找出此磁星有「短暫且高能爆發、中等持續與能量爆發、較長持續且溫和爆發、快速且低能爆發」現象,暗示了磁星爆發的多樣性並有不同的爆發機制。此外我們也發現磁星可能有「週期性」的現象,也許是自轉週期、地殼受的應力或磁場變化經過同樣時間累積(有週期性)而爆發。我們也比對有快速電波爆發 (Fast radio burst, FRB)的磁星SGR 1935+2154,看是否1E2259+586有FRB現象,結果暗示1E2259+586可能沒有FRB現象。

Wetting Tracing Paper—Fiber Porous Media Curling Behavior and Mechanisms

This research presents a novel approach to understanding the curling and uncurling behavior of tracing paper when exposed to water, identifying limitations in traditional diffusion-based models like Fick’s second law. While Fick's model adequately represents the uncurling phase, where water content is stable, it falls short during the curling phase due to its inability to account for dynamic changes in diffusivity. Our study identifies capillary action, modeled through Richards' equation, as the primary mechanism in the curling phase, where diffusivity varies with water content due to capillary-driven water movement through the paper's porous structure. Experimental data align well with the Richards' equation model, highlighting a saturation point where curvature peaks, governed by evaporation's impact on moisture balance. To simulate this phenomenon, we developed a finite difference approximation scheme based on Richards' equation, discretizing the spatial domain for detailed control over moisture dynamics and incorporating the Robin boundary condition with virtual points. This approach, combined with evaporation considerations, produces simulation results consistent with observed data, emphasizing evaporation’s role in steady-state moisture gradients and the subsequent deformation mechanics. Our findings further reveal that factors like paper thickness, temperature, and salt concentration significantly influence curling behavior. We established linear correlations between peak time and thickness reciprocal, as well as between peak curvature and thickness squared, supporting theoretical models. Temperature affects both peak curvature and curling rate due to changes in viscosity and surface tension, and higher temperatures prevent full uncurling due to sustained evaporation effects. Increased salt concentration heightens peak curvature without altering expansion ratio, suggesting additional variables in play.

探討高速轉盤風切聲的性質與原理

若使氣流流經轉動的有孔圓盤,將出乎意料產生明顯的聲音。一開始我們假設聲音之來源僅為氣流被圓盤切成一段段的疏密波,並以此基礎進行後續研究。但儘管已使用吸音棉等設備,且對錄下來的聲音傅立葉分析後,卻發現現象並非想像中的簡單。這當中仍有許多無法解釋的現象值得深入探討:包含基頻之相對振幅對比泛音顯得極小、還出現了馬達與氣閥以外的噪音等等。故隨後我們滾動式修正研究方法並尋找更多理論解釋和支持,譬如運用物理引擎 COMSOL 模擬、查詢各方面文獻及理論。 歷經此探究過程,我們最後觀察到顯著的一組諧波,其基頻等為洞數乘以轉動頻率,且第 n 個振幅隨著 n 增加逐漸遞減。我們基於《Siren Harmonics and a Pure Tone Siren 》 (E. A. Milne, R. H. Fowler, 1921)中提到的的諧波模型,加上利用 COMSOL 進行模擬,最後對所觀測的諧音序列提供定性定量解釋,以及證實其他的噪音乃風切現象所貢獻。

水中的奇妙力量探秘 沃辛頓射流

我們以實驗室及生活上容易取得的重物與乒乓球模擬網路上跳水彈射手中球體的沃辛頓射流實驗。結果發現以圓形的類天然海棉托住乒乓球丟入水中可成功產生射流,因此選擇此為托球的載體進行實驗。依據我們的實驗結果,至少需要15公分水深才能形成完整的射流彈射出乒乓球,原則上在下落軌跡完全垂直於水面時,落下高度越高,球體彈射高度越高,實際實驗水深15公分以上時,落下高度50公分彈射高度約可達47公分,但結果受限於托球的海綿在落下高度40公分後下落軌跡不穩定,若期望更高的射流強度需要尋找更穩定下落的載體。最後我們將實驗影片逐格分析計算,證實球體彈射過程是一個反覆受到重力及空氣阻力等因素影響降速,又受到下方射流水柱力量推擠而加速的過程,初步建立以乒乓球標示射流噴射過程運動模式的邏輯。

A Study on the Dynamics of Coupled Oscillators within Magnetic Environments

此研究針對磁力耦合振盪器進行理論建構與實驗設計,在理論建構中,我們先以彈力作為外力並推導公式,與實驗數據擬合後發現擬合參數極具參考價值。將磁力引入系統並推導公式,發現其與實驗數值擬合效果也極好。融合上述公式與參數後推廣出能描述振盪器運動模式之運動方程式,以Python數值模擬發現,此方程式與數據十分吻合且能產生波包與頻率下降等真實情況,故推論該運動方程式是有一定價值的。在傅立葉分析中發現了簡正模之應用,且當磁鐵初始距離越短或磁力強度越大時,振盪頻率都會有所提升,而初始位移不會造成影響。而本研究的成果將可透過一已知磁性量值之磁鐵求出另一板簧上物質之磁性量值,進而應用到新型機械式磁性雙板簧的懸臂磁力計設計。

腔體共振與開孔氣流的探討

本研究探討聲音共振引起腔體開口處氣流噴出的現象。實驗通過揚聲器播放聲音,使固定的錐形瓶產生共振,並改變聲音頻率、聲音強度及腔體參數(體積、瓶口截面積、瓶頸長度)分析氣流的形成原理與機制。腔體非共振情況下,腔體內外氣壓的振幅差較小,且存在相位差,此時開口處並未測得氣流;而在共振時,腔體內氣壓振幅顯著增加,導致開口處出現氣流且流速達到峰值。而流速峰值頻率與腔體幾何參數的關係符合修正後的亥姆霍茲共振公式,其中瓶頸有效長度應為L+1.45D。此外,氣流形態受衝程比L/D影響,當衝程比小於0.1時,氣體噴出後容易被重新吸回腔體,無法形成噴流;而衝程比大於0.4時,噴出氣流形成穩定的不連續渦流環,即合成噴流;在0.1至0.4之間時,氣流形態處於過渡狀態。本研究為聲能轉動能方面提供新的研究途徑,並有進階研究的可能性。

低速狀態下磁性齒輪傳動特性的實驗與理論探討

本研究探討利用指尖陀螺作為磁性齒輪,觀察並分析其磁性齒輪效應。本研究測量了磁性齒輪間的轉動慣量、影響範圍及力矩,除此之外,本研究發現,自由運轉狀態下的齒輪,具有三個運動階段,高速狀態,介於高速至低速難以預測的階段,以及低速的穩定運動狀態。 此外,為提升磁場計算的精確度,我們發現磁偶極近似方法無法有效描述系統中的磁場分佈,因此使用積分計算來求得更精確的磁場數據,並與實驗數據進行比對,結果吻合良好。

光程差與焦散影響下的雷射圖紋

本研究主要是研究雷射光通過瓶底的圖紋,出現多樣性的焦散曲線圖形。瓶底的圖紋有數字、花紋、環保標章等,焦散圖則是由亮暗相間一環一環的曲線組成的繞射圖。 研究分析焦散圖的共通性,有焦點、折皺、尖嘴、三曲、橢圓、雙曲、類牛頓環、海波、沙灘共九類基本單元圖,以數學函數方程式表示並探究圖形與玻璃的紋路結構的關係。 探討最外環的寬度的變化得知: 1.每個焦散圖最外環的亮帶最寬,然後依次寬度漸小。 2.圖紋到螢幕的距離、入射光波長與寬度呈線性增加。 3.入射角度、瓶底圖紋的曲率與寬度呈線性減小。 改變折射率,結果焦散圖形狀樣貌不變,縮小後仍然呈現立體狀。而且在水中最外環寬度與距離成正比,入射角度線性減小,波長線性增加趨勢。 未來希望能繼續探討複雜的焦散及 3D 立體的實像圖,應用於光學藝術的創作及室內設計上。