歡迎閱讀《週末科學版》！我們每週六都要為你介紹可以在家中進行的有趣科學實驗。你可以在《科學日誌》中記錄自己做了哪些活動，這樣就可以將所學的記錄下來，比較這些結果，也許還可以利用它們來設計新的實驗！先看一下《科學日誌》的點子再開始吧。展開實驗之前，記得要獲得大人許可喔！
In many ball sports, there is a rule that specifies the air pressure of the ball. Pressure is usually measured in psi (pounds per square inch). According to the NBA, a regulation basketball should be “inflated to 7.5 to 5.8 pounds pressure.” But why is it necessary to make such a rule? Why can’t umpires and referees just decide how much air to put in the ball? The answer is to do with the bounce. By regulating the air pressure, the players can be sure that the ball will bounce in a similar way as it did in the last game, and the game before that.(John phillips, staff writer)
In today’s experiment you will learn more about the correlation between air pressure and bounciness.
What you will need: a basketball, an air pressure gauge, a pump, stepladders, chalk, a video camera, a tripod and a meter stick.
許多球類運動都會明訂球壓標準。壓力常用的測量單位為「psi」（每平方英吋所承受的磅數）。根據全美籃球協會（NBA）的規定，每顆標準籃球的「球壓應該要介於7.5到5.8 psi」。但為什麼一定要有這種規定呢？為什麼裁判和評審不能自行決定球要充多少氣呢？答案和彈力有關。藉由規範球壓，選手們就可以確定球的彈力會和前場比賽，還有上上場比賽時差不多。（翻譯：袁星塵）
今天的實驗中，你將深入了解壓力和彈力的關聯性。
實驗所需：一顆籃球、一個球壓計、一個打氣筒、摺梯、粉筆、一台攝影機、一個三腳架和一把米尺。
Methodology
Step 1: Find a wall that you can mark with chalk. The side of a building will work well.
Step 2: Using the meter stick, chalk and step ladders, mark 10cm intervals on the wall from one meter up to three meters.
Step 3: Using the tripod, position your video camera so that it can capture all the markings on the wall. Set the camera to record.
Step 4: Record the pressure of the ball and drop it from the top of the stepladders.
Step 5: Use the pump to increase the pressure by 0.5psi. Drop the ball from exactly the same position. Repeat at least five times, recording the pressure before each drop.
方法
步驟一：找一面可以用粉筆作記號的牆，大樓的外牆效果不錯。
步驟二：用米尺、粉筆和摺梯在高一公尺以上、三公尺以下的區域，以每十公分為間距標上記號。
步驟三：用腳架架好攝影機，讓它可以捕捉到牆上所有的標記，然後按下錄影鍵。
步驟四：記錄球壓後，讓球從梯子頂端處自由落下。
步驟五：用打氣筒打氣加壓0.5psi，然後從同一個位置讓球自由落下。重複這個步驟至少五次，每次丟球前都要記下球壓。
Record the results
Step 1: Your video camera should have captured the height of each bounce. Freeze the shot when the ball is at its highest and record it next to the corresponding air pressure.
Step 2: Put the results in a graph. You should notice a correlation between the air pressure and the height of the bounce.
記錄結果
步驟一：你的攝影機應該有錄下每次球彈回的高度。在球彈到最高點時定格，把高度記錄在相對應球壓旁的欄位。
步驟二：將所有結果製成圖表，你就可以看出球壓和彈跳高度間的關聯。
Why it happened
The air molecules in the under-inflated ball are loosely packed. When the ball hits the ground, its surface stretches, and the energy is dissipated. In the heavily inflated ball, the air molecules are densely packed. When the ball hits the ground, the energy from the fall is stored and returned, projecting the ball upwards.
實驗原理
沒有充飽氣的球內，空氣分子鬆散，當球撞擊地面時，其表面展開，能量會逸失；充滿氣的球中，空氣分子密集，所以當球撞擊地面時，球落下所產生的能量會被貯存，並使球向上反彈。
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