The Physics of Fluids: Pressure, Buoyancy, and Flow in Philippine Contexts

The Physics of Fluids: Pressure, Buoyancy, and Flow in Philippine Contexts

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  Chico River, Cagayan— a familiar Philippine fluid in motion G EN ER AL S CI E NC E 1 1 • U NI T I : P HYSI CS • L ES SO N 4 The Physics of Fluids Pressure, Pascal's Principle, Buoyancy, and Bernoulli's Principle — how water, air, and everyday Filipino technology behave under pressure. 1 Interactive lesson deck • General Science 11
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  OV E RVIE W Have You Ever Wondered How Boats Stay Afloat? Fluids are an essential part of everyday life. Water flowing through rivers, the air we breathe, and even the blood circulating in our bodies are all fluids in motion. This lesson introduces the fundamental concepts that describe both static and flowing fluids — and connects them to real Philippine situations. ESSENTI AL QUESTION How do pressure, buoyancy, and flow explain the way fluids behave in nature and in the technologies we use every day? SUCCESS TARGETS By the end of this lesson, learners should be able to: 1 Identify applications of Archimedes' and Pascal's principles at home, in the community, in business, and in transportation. 2 Design simple, practical activities or models that test how shape, mass, and volume affect an object's ability to float. 3 Explain how Bernoulli's principle produces lift and why typhoon winds can blow roofs off houses. 4 Apply the hydrostatic pressure equation to real depth-and-pressure problems. General Science 11 — Fluids 2
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  FOU NDATI ONS Two Quantities Every Fluid Problem Starts With Fluids are substances that flow and take the shape of their container — this includes liquids and gases such as water and air. Rivers that irrigate farms, the wind and rain of a typhoon, and the blood in our bodies are all fluids at work. ρ Density A fundamental property equal to mass divided by unit volume. = m / V (SI unit: kg/m³) ρ Understanding density is key to Pascal's, Archimedes', and Bernoulli's principles. p Pressure How much force is applied per unit area. p = F / A (unit: N/m² or Pascal) 1.0 atm = 101 325 Pa = 760 mm Hg = 14.7 lb/in² = 1.013 bar General Science 11 — Fluids 3
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  CO NC EPT 1 Pressure in Fluids: It Grows With Depth The deeper you go underwater, the greater the pressure — this is why your ears hurt when diving, and why scuba divers need special equipment. In the atmosphere, pressure decreases as altitude increases, affecting weather systems and airplane performance. Fisherfolk know that setting nets deeper exposes them to stronger water pressure. p = p + gh ₀ ρ p₀ = pressure at the surface ρ = fluid density g = 9.8 m/s² h = depth WORKED EXAMPLE For a column of water at h = 10 m, ρ ≈ 1 000 kg/m³: p = (1 000)(9.8)(10) ≈ 9.8 × 10⁴ Pa (about 0.97 atm) WHY DAM WALLS ARE THICKER AT THE BASE Since p = ρgh, water pressure rises with depth. Engineers thicken dam walls near the base so they can withstand the much greater force pressing outward there — and reducing the water height behind a dam lowers the pressure on its base. WHY TYPHOON WINDS BLOW ROOFS OFF Fast-moving air above a roof creates lower pressure than the still air trapped inside the house (Bernoulli's principle). That pressure difference can be strong enough to lift the roof away. General Science 11 — Fluids 4
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  CO NC EPT 2 Pascal's Principle: One Push, Felt Everywhere Pressure applied to a confined, incompressible fluid is transmitted equally to all points within the fluid and its container. This is how hydraulic brakes, jacks, and presses amplify a small input force into a much larger output force. p = p F / A = F / A ₁ ₂ ₁ ₁ ₂ ₂ TRY IT A hydraulic press has a small piston of area 0.01 m² and a larger piston of area 0.5 m². If 100 N is applied to the small piston, what force is exerted on the larger piston? Real Philippine applications: car brake systems • hydraulic jacks for lifting jeepneys and tricycles • hydraulic presses in fabrication shops. Figure 1: Pressure exerted at A (p₁) equals pressure exerted at B (p₂). MISCONCEPTION CHECK “Applying pressure to a confined fluid increases pressure everywhere equally” is only true if the fluid is static and fully confined — local dynamic effects or open boundaries can change the distribution. General Science 11 — Fluids 5
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  CO NC EPT 3 Buoyancy: Why a Steel Ship Doesn't Sink Figure 2: A 5-kg object submerged in water displaces about 2 kg of water — the buoyant force equals the weight of water displaced. The buoyant force on an object submerged (fully or partially) in a fluid equals the weight of the fluid the object displaces. An object floats when it is less dense than the fluid, or when its weight equals the buoyant force acting on it. F_B = _fluid × V_displaced × g ρ ⛵ Bangkas & fishing boats stay afloat by displacing enough water. 🦺 Life vests support a wearer's weight using the same principle. 🚢 Steel ships float because their hollow hulls displace a large volume of water. General Science 11 — Fluids 6
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  APP LY IT Will the Boat Float? THE PROBLEM A hollow metal boat has a total volume of 2.0 m³ and a mass of 600 kg when empty. Will it float on seawater (ρ = 1 025 kg/m³)? How much additional load can it carry before sinking? 1 Max buoyant force available F_B = ρ_sw × V × g = 1 025 × 2.0 × 9.8 ≈ 20 090 N 2 Weight of the empty boat W = mg = 600 × 9.8 = 5 880 N 3 Since F_B > W, the boat floats — with room for more load Additional load = (20 090 − 5 880) / 9.8 ≈ 1 450 kg REMEMBER A hollow shape submerges only part of its volume until the water it displaces weighs as much as the whole boat plus its load. A wooden block (ρ ≈ 600 kg/m³) floating in fresh water (ρ = 1 000 kg/m³) sits with about 60% of its volume submerged — the ratio of the two densities. Rescue teams use lightweight inflatable boats in flooded areas for exactly this reason: they displace a large volume of water relative to their own weight. General Science 11 — Fluids 7
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  CO NC EPT 4 Bernoulli's Principle: Faster Flow, Lower Pressure For the steady flow of an incompressible, non-viscous fluid along a streamline, the sum of pressure energy, kinetic energy per unit volume, and potential energy per unit volume stays constant. In practical terms: where a fluid speeds up, its pressure drops — and the other way around. p + ½ v ² + gh = p + ½ v ² + gh ₁ ρ ₁ ρ ₁ ₂ ρ ₂ ρ ₂ p = pressure (Pa) ρ = density (kg/m³) v = speed (m/s) g = 9.8 m/s² h = height (m) Air moves faster over a wing's curved top than below it, creating a pressure difference that lifts an airplane — the same idea behind a typhoon peeling off a roof. THREE PRINCIPLES, ONE STORY Pascal's Explains pressure transmission in confined fluids (brakes, jacks). Archimedes' Explains buoyant forces in static fluids (ships, life vests). Bernoulli's Explains energy behavior in moving fluids (lift, storm winds). General Science 11 — Fluids 8
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  EV E RYDAY F LU I DS Fluid Physics Applications in the Real World 🚰 Water Supply Fluid principles maintain consistent pressure and flow in community pipelines. ⛵ Boats & Ships Fluid buoyancy and flow keep hulls stable and efficient on water. 🔧 Hydraulic Machinery Brakes and jacks use Pascal's principle to amplify force and lift heavy loads. 🏥 Medical Devices IV lines and household tools use fluid dynamics like the Venturi effect. ️ ⛈️ Weather & Ocean Fluid principles explain wind patterns, currents, and storm formation. 🌾 Agriculture Irrigation and spraying equipment rely on fluid flow and pressure. 🌊 Natural Phenomena River flow, waves, and fish movement are governed by fluid dynamics. ⚡ Hydropower Water flow and pressure differences are harnessed to generate electricity. General Science 11 — Fluids 9
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  G RO UP AC TI V I TY Smart Moves: What Makes an Object Float? Form groups of three to four. Follow the engineering design process to test whether shape, mass, or volume affect floating in water. 1 Define How can we design a model or activity to test whether shape, mass, or volume affect floating? 2 Imagine Sketch two designs — e.g. a clay ball vs. a clay boat, or a heavy object in a lightweight container. 3 Plan Decide how you will vary one property at a time (shape, mass, or volume). 4 Build & Test Place each model in water. Record whether it floats or sinks, and how it behaves. 5 Redesign If a model sinks, think of changes that could make it float. Test again. 6 Discuss Present your results. Classmates ask follow-up questions about the science behind your design. General Science 11 — Fluids 10
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  PRO G RESS SNAP SH OT Quick Quiz: How Are You Doing? Choose the best answer for each item, then check the answer key on the next slide. 1 During a typhoon, the roofs of poorly built houses are often blown off. Which principle best explains this? A. Pascal's principle B. Archimedes' principle C. Bernoulli's principle D. Torricelli's theorem 2 A submerged object feels lighter in water than in air. Which explanation best describes this? A. Its density decreases in water B. It loses weight from absorption C. Buoyant force partly balances its weight D. Pressure above equals pressure below 3 Two identical containers are filled, one with water and one with oil. The water exerts greater pressure at the bottom. Which factor is most responsible? A. Shape of the containers B. Viscosity of the fluids C. Densities of water and oil D. Surface area of the containers General Science 11 — Fluids 11
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  ANSW E RK E Y Quick Quiz — Answers & Reasoning 1 C — Bernoulli's principle Faster-moving air above the roof creates lower pressure than the still air inside, and the pressure difference lifts the roof. 2 C — Buoyant force partly balances weight The upward buoyant force (Archimedes' principle) offsets part of the object's weight, so the scale reads less. 3 C — Densities of water and oil Hydrostatic pressure depends on fluid density: p = ρgh. Water is denser than oil, so it exerts more pressure at the same depth. General Science 11 — Fluids 12
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  CR EATI NGMEANI NG F U L CO NN EC TI ONS Core Value: Preparedness The physics of fluids helps us understand natural events that significantly impact Filipino lives — floods, storm surges, and typhoons. Knowing how water and wind behave can make the difference between safety and danger. • Understanding water pressure and flow explains why floodwaters rise rapidly in low-lying areas and why storm surges produce dangerous currents. • Understanding air pressure and wind patterns helps us comprehend the formation and strength of typhoons. • Connecting scientific understanding to real-life situations empowers us to protect ourselves, our families, and our communities. REFLECT How does understanding the physics of fluids influence the way you think about and prepare for floods and typhoons in your community? “I can use what I learned about fluids to make a difference by ___________________.” General Science 11 — Fluids 13
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  K n ow l e d g e • S k i l l s • A tti t u d e s • A c ti o n s Fluids Are Everywhere — Now You Can Explain Them. Pressure • Pascal's Principle • Buoyancy • Bernoulli's Principle General Science 11 | Unit I: Physics | Lesson 4: Fluids