Chapter 10 – Transfer of Heat Energy & Its Effects

Heating: Objects expand (get bigger) because particles move further apart. Density decreases.
Cooling: Objects contract (get smaller) because particles move closer together. Density increases.
Extent of change: Gases > Liquids > Solids.
\text{density}=\dfrac{\text{mass}}{\text{volume}}
Engineers design structures to handle these size changes (e.g., gaps in roads, loose power cables).

Opening jar lids: Hot water expands metal lid.
Bimetallic strip: Two metals joined, bends when heated/cooled due to different expansion rates (used in thermostats, thermometers).
Liquid-in-glass thermometer: Liquid expands/contracts in a thin tube.
Hot-air balloon: Hot air becomes lighter (less dense) and rises.

Conduction:
- Heat moves through a material without the material itself moving (particles bump).
- Best in solids. Metals are good conductors, wood/air are insulators.
Convection:
- Heat moves by the actual movement of liquids or gases (fluids).
- Hot fluid gets lighter, rises; cool fluid sinks, creating a cycle (e.g., boiling water, air conditioners, land/sea breezes).
Radiation:
- Heat moves via electromagnetic waves, no medium needed (e.g., Sun's heat).
- Dark/dull/rough surfaces absorb and emit heat best. Light/shiny surfaces reflect heat.

Conduction: Frying pans (metal base, insulating handle), wool clothing (traps air), double-glazed windows (trapped air).
Convection: Electric kettles (heater at base), air conditioners (mounted high).
Radiation: Black hotplates (good emitters), silver kettles (poor emitters), light-colored clothes (poor absorbers).
Integrated Designs:
- Spacesuit: Insulating layers, white outer layer.
- Vacuum flask: Plastic cap, silvered double walls, vacuum (stops conduction/convection).

Heating causes expansion, cooling causes contraction.
Expansion/contraction affects volume and density, crucial for convection and buoyancy.
Materials conduct heat at different rates.