Forces and Energy Notes

9.1 How Do Forces In Nature Affect Us

• Climate change increases sea surface temperatures.
• This increases intensity/frequency of natural disasters like:
  • Tropical cyclones (heavy rain, strong winds - up to 200 km/h, flooding, landslides).
  • Earthquakes (plates slide, release destructive energy).
  • Volcanic eruptions (magma pushed out, releasing heat, light, and kinetic energy).
  • Tsunamis (earthquakes/eruptions cause powerful waves up to 40 meters).

9.2 What are the Types of Forces?

• Forces:
  • Contact (physical contact)
    • Friction (opposes motion).
    • Elastic force (resistance to change in shape).
  • Non-contact (no physical contact).
    • Gravitational force (attracts objects with mass).
    • Weight (gravitational force on an object).
    • Magnetic force (between magnets/magnetic materials).
• Weight vs. Mass:
  • Weight: gravitational force (N).
  • Mass: amount of matter (kg).
  • Weight changes with location; mass remains constant.
  • Spring balance measures force/weight.
  • Electronic/beam balance measures mass.

9.3 What Happens When Two Or More Objects Interact?

• Force interactions transfer energy, causing changes:
  • Motion (start, stop, speed, direction).
  • Turning effects (levers, spanners).
  • Size/shape (kneading).
  • Pressure (force per area).
• Pressure: $Pressure = Force / Area$ (N/m² or Pa).
  • Everyday Applications
    • Pressure in Liquids (increases with depth; submarines, dams).
    • Atmospheric Pressure (air exerts pressure; straws, suction cups).
• Work:
  • Transfer of energy when a force causes movement in the same direction.
  • Conditions: force applied, object moves, object moves in the direction of the force.

9.4 How Is Energy Conserved?

• Law of Conservation of Energy: Energy cannot be created/destroyed, only converted.
• Forms of energy: electrical, sound, light, heat, chemical, elastic, gravitational, kinetic.
• Total energy = useful energy + energy transferred to surroundings.
• Examples:
  • Archery: chemical potential → elastic potential → kinetic.
  • Swing: gravitational potential ↔ kinetic.

9.5 What Are The Sources Of Energy That We Use?

• Fossil Fuels (non-renewable):
  • Burning produces air pollutants and greenhouse gases causing global warming.
• Renewable Energy:
  • Solar: light → electrical (solar cells); no pollution.
  • Hydroelectric: gravitational potential → kinetic → electrical; may cause flooding.
  • Wind: kinetic → kinetic (turbine) → electrical; may harm wildlife, noise pollution.
  • Geothermal: heat → kinetic → electrical; land use, toxic elements.
  • Biofuels: chemical potential → heat → kinetic; partially offsets carbon emissions.
  • Nuclear: nuclear → heat → kinetic → electrical; clean, but waste disposal is a challenge.