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.