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Buoyancy, Archimedes' principle, and Pascal's.pptx

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Buoyancy, Archimedes' principle, and Pascal's principle
🎯 Learning Objectives Students will be able to: Describe Pascal’s and Archimedes’ principles. Explain buoyant force and floating/sinking using density and displacement. Today we’ll discover why boats float, how submarines dive, and how balloons rise!
BUOYANCY Have you ever tried to push a beach ball underwater? What happened? this magical force called buoyant force It pushes back and floats up
BUOYANCY Buoyant force: It’s the upward force that fluids like water or air give to anything placed in them. If an object pushes aside (displaces) some fluid, the fluid pushes back with a force equal to the weight of the fluid displaced.
But why does this force happen? Fluids don’t just sit there—they’re constantly applying pressure in all directions. guess what? The deeper you go in a fluid, the more pressure it has. The water underneath an object pushes harder than the water above it. This creates an upward force That's the buoyant force.
Q: Why do some things, like a stone, sink instead of float? It all depends on a battle of forces—who's stronger? Weight: The downward pull of gravity. Buoyant Force: The upward push from the fluid. If the object’s weight wins = 💥 it sinks. If buoyant force wins = 🎉 it floats.
Density and Buoyant Force Density: the amount of mass in a given volume. If the average density is … … equal to water, the object will float. … greater than water, the object will sink. … less than water, the object will rise. More dense = heavier. Less dense = lighter.
Density and Buoyant Force Ice: is less dense than water. That’s why ice floats along the ocean surface. Oil: is less dense than water. So oil floats instead of mixing in water. Helium: is less dense than air. That’s why your birthday balloons float to the ceiling. https://simpop.org/buoyancy/buoyancy.htm
Buoyant Force Buoyancy force depends upon two factors: Amount (Volume) of liquid displaced by the object The density of the object.
Object Displaced Water Buoyant Push Sink/Float Iron nail Very little Very weak Sinks Steel ship Tons Very strong Floats Buoyant Force Buoyancy force depends upon two factors: Amount (Volume) of liquid displaced by the object The density of the object.
Questions What is buoyant force? 🔘 A. The downward pull of gravity on an object in a fluid 🔘 B. The force that keeps solid objects from moving 🔘 C. The upward force a fluid applies to an object in it 🔘 D. A sideways force from wind or air
Questions What is buoyant force? 🔘 A. The downward pull of gravity on an object in a fluid 🔘 B. The force that keeps solid objects from moving 🔘 C. The upward force a fluid applies to an object in it 🔘 D. A sideways force from wind or air
Questions You have a block of wood, a rubber duck, and a marble. How could you predict which will float and which will sink without testing them in water? Compare their densities to water. Objects with lower density than water (wood and rubber duck) will float, and objects with higher density (like the marble) will sink.
ARCHIMEDES’ PRINCIPLE Any object completely or partially submerged in a fluid experiences an upward force equal in magnitude to the weight of the fluid displaced by the object.
ARCHIMEDES’ PRINCIPLE Force Balance Inside a Fluid An object submerged in a fluid feels two main forces: • Gravity (its weight) pulling it downward • Buoyant force (upthrust) pushing it upward due to fluid pressure differences. The object’s apparent weight is the net force after upthrust partially cancels out gravity. Apparent weight= Weight of object (in the air) – Thrust force (buoyancy)
ARCHIMEDES’ PRINCIPLE The “weight lost” when an object enters a fluid is exactly equal to the weight of the fluid displaced. apparent weight loss = weight of fluid displaced
•ρ is the density (in kg/m³ or g/cm³), •V is the volume (in m³ or cm³). •g is the gravity ( in Newton per kilogram (N/kg)) •m is the mass (in kg or g), ARCHIMEDES’ PRINCIPLE FORMULA Formula: Buoyant Force = ρ × V × g ρ = density of fluid | V = volume displaced | g = gravity
Archimedes’ Principle Derivation Weight = mass x acceleration due to the gravity Weight = mass x gravity Weight = density x volume x gravity mass = density x volume From Archimedes’ principle, we know that the apparent loss of weight is equal to the weight of the water displaced therefore the thrust force is given by the following equation: Formula: Buoyant Force = ρ × V × g ρ = density of fluid | V = volume displaced | g = gravity
Wood has density of 0.53 g/. What is the volume of 33.3 g of wood? Given density = 0.53 g/ mass = 33.3 g volume = ? = V = = 62.8
ARCHIMEDES’ PRINCIPLE Term Definition Actual Weight Force of gravity on the object in air Buoyant Force Upward force equal to weight of displaced fluid Apparent Weight What you feel in the fluid: gravity – buoyant force Displaced Fluid Fluid volume equal to object’s submerged volume Archimedes’ Law Buoyant force = Weight of displaced fluid
Pascal's principle A pressure change in one part of a fluid is transmitted equally throughout the fluid.
Pascal's principle When a ball is inflated, the pressure at the entrance is increased. The air is distributed evenly in the ball. The pressure exerted by the air on the ball wall will then be equal in all directions.
What Is Pressure? Pressure measures how much force is distributed over an area Pressure = Force ÷ Area Shows • If you push harder = more pressure 💪 • If you push on a smaller area = still more pressure! Pressure (P) = Force / Area, is the Pascal (Pa), which is equivalent to one Newton per square meter (N/m²). Force (F): is typically measured in Newtons (N). Area (A): is typically measured in square meters (m²).
What Is Pressure? Force = Pressure × Area shows how the same pressure on a larger area makes a bigger force
Activity Press your finger gently against a balloon. Now poke it with a pencil. Surface Area Resulting Pressure Finger Large Low pressure — not enough to pop the balloon Pencil Tip Tiny High pressure — easily punctures the balloon
A Squeezable Example! Let’s bring a tube of toothpaste! You squeeze anywhere on the tube. toothpaste shoots out the opening. That’s Pascal’s Law at work! • You apply pressure. • The pressure travels through the toothpaste. • Toothpaste escapes where there’s an opening.
Hydraulic Brakes! You step on the brake pedal with a small force. Force = Pressure × Area the bigger area multiplies the force to stop the car! That force creates pressure in a fluid. That pressure travels through the brake fluid to larger brake cylinders.
What’s Pascal’s Law? ✍ Your turn! Say it out loud or write it in your own words.