📙 Advanced (960~1050) | Why Do We Feel Lighter in Water?

물속에서 몸이 가볍게 느껴지는 과학적 이유는 무엇일까요?

✔ 학습 목표 제시
부력의 원리를 아르키메데스 법칙을 통해 이해하고, 밀도와 부피 개념도 함께 배워요.

🔹 Reading Passage
When you enter a body of water, such as a swimming pool, you may experience a noticeable reduction in your body’s apparent weight. This sensation is not a mere illusion; rather, it results from a physical force known as buoyancy, which is a core concept in fluid mechanics.

Buoyancy refers to the upward force exerted by a fluid on an object that is placed within it. This force acts in opposition to gravity and can reduce the effective weight of the object. The principle was first identified by the Greek scientist Archimedes, who observed that submerged objects are pushed upward by a force equal to the weight of the fluid they displace.

According to Archimedes’ Principle, an object immersed in a fluid will float if it displaces an amount of fluid equal to or greater than its own weight. If it displaces less, it will sink. This explains why some objects float easily while others do not—it depends on the relationship between the object’s weight and the volume of fluid it displaces.

Two primary factors influence how strong the buoyant force is: the density of the fluid and the volume of the displaced liquid. This is why people feel lighter in denser liquids like seawater compared to freshwater. It is also why ships made of heavy materials can float—they are shaped to displace a large enough volume of water to support their weight.

🔹 Reading Comprehension Question 1
Q1. What causes the feeling of lightness in water?
A. The cooling effect of water
B. The salt in the water
C. The upward force called buoyancy
D. The slowing of gravity

🔹 Reading Comprehension Question 2
Q2. Why do ships made of heavy materials still float?
A. They are light inside.
B. They heat the water around them.
C. They displace a large enough volume of water.
D. They are pulled upward by wind.

🔹 Vocabulary Quiz
Q3. What does the word “displace” mean in the passage?
A. to destroy
B. to move aside
C. to replace
D. to push out of position

🔹 Grammar Quiz
Q4. Choose the correct sentence using passive voice:
A. The water pushes the object up.
B. The object push by water.
C. The object is pushed up by the water.
D. The object is push up the water.

🔹 어휘 정리표

영어 단어	영어 뜻	한글 뜻	예문
buoyancy	upward force in a fluid	부력	Buoyancy helps people float in water.
displace	to move something out of its place	밀어내다, 대체하다	Ships displace water to stay afloat.
density	mass per unit volume	밀도	Salt water has higher density than freshwater.
gravity	force pulling objects toward Earth	중력	Gravity pulls objects downward.
apparent	seeming, not actual	겉보기의	Your apparent weight feels less in water.
immerse	to put into a liquid fully	잠기다	He immersed the stone in water.
volume	the amount of space an object takes	부피	A large volume helps ships stay afloat.
exert	to apply (a force)	(힘을) 가하다	Water exerts pressure on all sides.

✔ 정답 및 해설
Q1. What causes the feeling of lightness in water?
정답: C – The upward force called buoyancy
→ The passage explains that buoyancy is what makes people feel lighter in water.
🔻 A: Cooling is mentioned nowhere.
🔻 B: Salt is mentioned as part of density but not directly the cause.
🔻 D: Gravity is not weakened but countered by buoyancy.

Q2. Why do ships made of heavy materials still float?
정답: C – They displace a large enough volume of water
→ Ships float because of the water they displace.
🔻 A: 내부의 가벼움은 관련 없음
🔻 B: 물을 가열하는 내용 없음
🔻 D: 바람은 부력과 무관

Q3. What does the word “displace” mean in the passage?
정답: D – to push out of position
→ “Displace” is used in the context of replacing the water.
🔻 A: destroy는 본문의 의미와 다름
🔻 B: move aside는 부적절
🔻 C: replace와도 다름

Q4. Choose the correct sentence using passive voice:
정답: C – The object is pushed up by the water.
→ Passive voice with “is + past participle” is used.
🔻 A: 능동태 문장
🔻 B: 동사형 오류
🔻 D: 문법 구조 오류

✅ Extra Grammar Note:
Passive voice uses be + past participle.
– 수동태는 be동사 + 과거분사 형태로 구성돼요.

🔁 문법 복습 문제
Choose the correct passive sentence:
A. The stone pushed into the water.
B. The stone was pushed into the water.
C. The stone push into water.
D. The water was pushing the stone.

정답: B

📝 수동태는 ‘was pushed’처럼 be + 과거분사 형태로 써요.

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