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動靜皆有「能」!!
913 的理化課
你看到什麼?
913 的理化課
為什麼要倒水?
913 的理化課
位 能
當物體的【 位置高低 】 或
【 形狀 】 改變時,此時外力對
物體所做的功,轉換成物體另一種
形式的能量,稱為【 位能 】。
常見的位能有兩種形式:
【 重力 】位能、【 彈力 】位能。
動手做研究
• 軌道上的彈珠從高處落下來,經過平
台發射,水平射程有多遠?
實驗次數 起始高度 水平距離
1
2
3
請把握時間
只有5分鐘!!
動手做研究
• 軌道上不同質量的彈珠從高處落下來,
打到小球,小球的水平射程有多遠?
實驗次數 被大彈珠撞 被小彈珠撞
1
2
3
請把握時間
還是只有5分鐘!!
重力位能
• 相同條件下,物體的重力位
能和其質量大小成【 正 】
比,也和其高度變化大小成
【 正 】比。
913 的理化課
重力位能
• 公式:
重力位能 =
質量 × 重力加速度 × 高度
U = m × g × h
單位
Test Time 1
一個5kg的西瓜放在1m高的桌上,
則西瓜對地板的重力位能大小為
多少?
49 J。
Test Time 2
500公克的一杯珍奶離地100cm
高時,對地面的重力位能大小為
多少?
4.9 J 。
搶答題
有A、B、C三物體質量分別為
5kg、2kg、3kg,分別置於地面
上方5m、6m、8m處,則何者
對地面的位能最大?【 A 】
把懸吊的球拉高,
然後
放手!
913 的理化課
把蕭敬騰放到最危險,
但安全的位置!
913 的理化課
把蕭敬騰換成你,
站在那個位置!
913 的理化課
重力位能與動能的轉換
• 位能與動能可互相轉換,
將位能與動能的總和
稱為【 力學能 】。
913 的理化課
重力位能與動能的轉換
• 若物體只受【 重力 】而沒
有其他外力作用時,動能和
位能總和將保持不變,稱為
【 力學能守恆 】。
913 的理化課
自由落體的力學能
913 的理化課
• 單擺的力學能
滑板玩家要如何才能過中央山坡
如果有摩擦力會不會不同?
組合一種軌道,讓滑板玩家玩一玩
彈力位能
物體(彈性體)因形變
而具有作功的能,
稱為【 彈力位能 】
913 的理化課
橡皮筋彈射「紙彈」實驗
913 的理化課
實驗次數 橡皮筋
拉長長度
紙彈飛行
水平距離
1
2
3
彈簧的力學能守恆
(1)將圓球拉至A點,使其伸長
X距離,彈簧即儲存了彈性位能。
913 的理化課
彈簧的力學能守恆
在A點時,形變量
最大,
位能【 最大 】;
速率為【 零 】,
動能為【 零 】。
913 的理化課
彈簧的力學能守恆
放手後,圓球受彈
簧的彈力的影響,
向【 左 】運動。
到B 點之前,
動能【 】
位能【 】
913 的理化課
(2)
彈簧的力學能守恆
(3) 通過B點時,
位能為【 零 】;
速度【 最大 】,
動能【 最大 】。
913 的理化課
彈簧的力學能守恆
(4)彈簧繼續向左
壓縮至-X的距離。
到C 點之前,
動能【 】
位能【 】
913 的理化課
彈簧的力學能守恆
(5)到達C點時,
形變量最大,
位能【 最大 】;
速率為【 零 】,
動能為【 零 】
913 的理化課
生活中那裡用到
力學能的轉換?
913 的理化課
你的彈簧筆
可以彈多高?
913 的理化課

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位能與動能的轉換