一架圓柱體係佢既船身旁邊下部開孔，之後灌水入去個圓柱體入面

呢一樣野可以用flow rate 來explain.

無論開大孔定係細孔柱入面d 水都會係一樣咁多, 所以pressure at the hole 都會係一樣的, agree?

而 F= PxA; F = mQ; Q=AV <==F 係force, m= 係mass of water, Q 係 flow rate, A 係area of opening, V 係speed of water eject from the hole, 當combine 晒所有equation, 我地會得到:
constant = AV, 咁A 細 V 就大, 而V 大的話, 即係架ship 的velocity 大啦 <== 呢個係depends on action and reaction 啦.

解得好似有d 唔係幾好, 希望你明啦

Newton's Third Law of Motion
Identifying Action and Reaction Force Pairs
According to Newton's third law, for every action force there is an equal (in size) and opposite (in direction) reaction force. Forces always come in pairs - known as "action-reaction force pairs." Identifying and describing action-reaction force pairs is a simple matter of identifying the two interacting objects and making two statements describing who is pushing on who and in what direction. For example, consider the interaction between a baseball bat and a baseball.

Newton's Third Law of Motion
Identifying Action and Reaction Force Pairs
According to Newton's third law, for every action force there is an equal (in size) and opposite (in direction) reaction force. Forces always come in pairs - known as "action-reaction force pairs." Identifying and describing action-reaction force pairs is a simple matter of identifying the two interacting objects and making two statements describing who is pushing on who and in what direction. For example, consider the interaction between a baseball bat and a baseball.


The baseball forces the bat to the leftt (an action); the bat forces the ball to the right (the reaction). Note that the nouns in the sentence describing the action force switch places when describing the reaction force.

Consider the following three examples. An action force is stated; determine the mutual reaction force that forms the action-reaction force pair. Use the "pop-up menu" to view the answer.


Baseball pushes glove leftwards.

Enclosed air particles push balloon wall outwards.

Check Your Understanding
1. Consider the interaction depicted below between foot A, ball B, and foot C. The three objects interact simultaneously (at the same time). Identify the two pairs of action-reaction forces. Use the notation "foot A", "foot C", and "ball B" in your statements. Depress the mouse on the "pop-up menu" to view the answer.