It is said that Galileo Galilei (1564 - 1642), an Italian Scientist, dropped a small iron ball and a large cannon ball from the top of the Leaning Tower of Pisa. He found that the two balls reached the ground at almost the same time.
Which of the following is/are correct deduction(s) from this experiment?
(1) The two balls fell with the same acceleration.
(2) A body will maintain uniform motion if there is no external force acting on it.
(3) The gravitational forces acting on the two balls were identical.
請解釋點解 (1) 係岩, (2) 係錯
我對 (1) ge 理解係
F=ma
W - air resistance F = ma
a = mg - F / m
唔係mass 越大, acceleration 就越大咩?
(2) 點解會錯ge??
air resistance 唔係會同 mg balance ge咩?
唔係balance 左 就冇net force 咩? 咁唔係constant velocity 咩?
但係佢答案話係得 (1) 岩...
求救, 唔該!!!!!!!!!!!!!
[急!!!!!!!!!] 20分!!!! f.4 phy
2009-01-01 2:21 am
回答 (3)
2009-01-01 3:05 am
✔ 最佳答案
你想得太多了。Galileo這個實驗，air resistance的作用是小得可以忽略的。(1): Since the two balls move with the same distance in a given time interval. We can deduce that they have the same state of motion in any given time. Hence, we say they have the same acceleration.
(2): In this experiment, we cannot deduce this statement. Since we actually do not know whether there is an external force acting on the system. This is not the nature of the experiment. So this is wrong.
(3): By Newton's 2nd law of motion,
F = ma
Since they have the same acceleration, and different masses. So the gravitational force acting on them are different.
2009-01-04 12:15:11 補充：
Acer81996 (回答者003)的concept有點錯。 Galileo這個實驗並不是在真空環境下進行的。
你的第一句statement，是根據牛頓萬有引力定律(AL課程)中可求得，物體自由落體的加速度是與物體本身的質量無關。
參考: Myself~~~
2009-01-03 10:23 pm
1.唔係mass 越大, acceleration 就越大咩?
A:mass 越大, kinetic energy 就越大, 不是 acceleration
2.A:surface area 太細，air resistance 自然就會很微小。
在一個真空環境，任何東西都不會有air resistance，所以這個可以忽略。
A:mass 越大, kinetic energy 就越大, 不是 acceleration
2.A:surface area 太細，air resistance 自然就會很微小。
在一個真空環境，任何東西都不會有air resistance，所以這個可以忽略。
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