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Grade 8 Fluid Mechanics Overview

May 22, 2025

Grade 8 Study Sheet – Fluids

Lesson 1: Introduction to Fluids

  • Definition of Fluids: Materials with no fixed shape, free to flow, like liquids and gases.
    • Example: Water

Lesson 2: Characteristics of Fluids (Laminar and Turbulent Flow)

  • Particle Theory of Matter
    • Explains composition and behavior of matter.
    • Postulates:
      • Matter is made of tiny particles.
      • Particles have empty spaces between them.
      • Particles move randomly all the time.
      • Particles move faster and spread apart when heated.
      • Particles attract each other.
  • Types of Fluid Flow
    • Laminar Flow: Smooth, regular, parallel movement. Example: Rivers and Canals.
    • Turbulent Flow: Choppy, irregular motion. Example: Rapids.
    • Streamlined Objects: Reduce turbulent flow, aerodynamic. Example: Dolphins.

Lesson 3: Flow Rate and Viscosity

  • Key Definitions:
    • Viscosity: Resistance to flow.
    • Cohesion: Attraction between like particles.
    • Adhesion: Attraction between unlike particles.
    • Surface Tension: Strong attraction forming the surface of a liquid.
    • Flow Rate: Speed of fluid movement, measured in volume/time (e.g., L/s).
  • Flow Rate Calculations:
    • Example 1: Faucet - 0.2 L/s or 720 L/h.
    • Example 2: Baby bottle - 5 mL/min or 0.08333 mL/s.

Lesson 4: Density

  • Definitions:
    • Mass: Amount of matter.
    • Weight: Gravity's force on an object.
    • Volume: Space an object occupies.
  • Volume Calculation Methods:
    1. Measurement - Length × Width × Height.
    2. Displacement - Water rises when an object enters.
    3. Overflow Can.
  • Density Relationship:
    • Increase mass + constant volume = increased density.
    • Increase volume + constant mass = decreased density.
  • Density as a Characteristic Property: Unique, consistent measure irrespective of sample size.
  • Floating Objects:
    • Higher density than liquid = sinks.
    • Lower density than liquid = floats.
    • Same density = stays in place or moves if other objects are introduced.

Lesson 5: Calculating Density

  • Definitions and Formula:
    • Density: Compactness of a substance.
    • Formula: Density = Mass/Volume.
  • Units:
    • Mass in grams (g) or kilograms (kg).
    • Volume in liters (L), milliliters (mL), cubic centimeters (㎤), or cubic meters (㎥).

Lesson 6: Buoyancy and Displacement

  • Definition and Example:
    • Buoyancy: Upward force in a fluid. Example: Ship.
  • Ship Floating Mechanism: Displaces water using a hollow shell, increasing buoyant force, reducing density.
  • Buoyancy Types:
    • Positive: Less dense than fluid, floats.
    • Negative: More dense, sinks.
    • Neutral: Same density, remains suspended.
  • Archimedes’ Principle: Buoyant force equals weight of the displaced fluid.

Lesson 7: Fluids Under Pressure

  • Confined Fluids:
    • Definition: Fluids in a closed system, cannot enter or leave.
    • Example: Blood in the circulatory system.
  • Compressibility:
    • Gases: Particles far apart, compressible.
    • Liquids: Particles closer, almost incompressible.
  • Car Brakes: Hydraulic system using fluids.
  • Pneumatics: Gases under pressure, examples include dentist drills and bicycle pumps.
  • Hydraulics: Liquids under pressure, examples include car braking systems.
  • Hydraulic System Components:
    • Pump, Conductors, Valves, Pressure Gauge, Arm Cuff.

Lesson 8: Fluids in Real Life

  • Temperature and Pressure Effects:
    • Compressing gases decreases volume.
    • Heating gases increases particle spread.
    • Compressed gas may liquefy (e.g., Propane Gas).
  • Aerosol Can Danger:
    • Heating increases particle speed and pressure, risk of explosion.
  • Valves in Circulatory System:
    • Ensure correct blood flow, prevent backflow.
  • Valve Malfunction:
    • Causes blood pooling, leads to varicose veins.