垂直水柱的成節機制探討

科展類別
臺灣國際科展
屆次
2007年
科別
物理科
學校名稱
國立高雄師範大學附屬高級中學
指導老師
簡聿成、徐德耀
作者
徐悅群、楊亭亭
關鍵字
垂直水柱,成節機制

摘要或動機

本研究欲探討垂直水柱遇障礙物成節的形成機制。以數位照相機、光電計時器等進行觀測。 實驗結果如下: (一)因往返水柱波速不同,而且節無波腹大幅振動現象,故節不是駐波現象。 (二)細針插入水柱表面時,當針上方超過某長度後,針下方產生V字形震波。但不論針相對水柱的速度是否超過波速,針上方都有節,故不是震波所產生的現象。 (三)根據水波槽模擬實驗,不論木條是否超過波速,木條前方均產生波紋。木條前方的水受到木條推動,往前方加速,因此顯現出波紋了。 我們認為,在水柱中所看到的節,不是震波或駐波,而是相對於木條往前傳遞的波。波源是撞擊物,改變了水柱表面的壓力,而成為波源,水柱的水因受撞擊,某個範圍內流速會小於波速,使得撞擊物前方存在波紋。This experiment uses digital camera and photoelectric timer to discuss the mechanism of causing spouts to form nodes on its surface. Because the downward wave velocity of the spout is different from that upwardand there are no significant vibrations of antinodes, standing waves are not the mechanism of causing nodes. In the experiment of inserting a needle into the spout, we found out that while the needle was inserted above a certain length of the spout, v shaped bow waves emerged. However, no matter the velocity of the needle related to the spout is over the wave velocity, there are always nodes above the needle. Therefore, bow waves are not the mechanism of causing nodes. According to the ripple tank simulating experiment, no matter whether the speed of the wooden stick is faster than the wave velocity or not, there are always waves forming in front of the wooden stick. The wooden stick pushes water in front of it and causes the water to accelerate forward. Therefore, waves appear. We think that the nodes we see on spouts are neither standing waves nor bow waves. The nodes are rather caused by the relatively moving wooden stick. The object, which impacted the spout (wooden stick), changed the pressure of the spout’s surface and became the source of wave. Because of the impact, the velocity of the water current of a certain area became slower than the wave velocity and causes nodes forming on the surface of the spout.


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