PHYSICS - Thermal energy

Heat

a form of energy that transfers from a hotter object to a cooler one

Why do heat transfers stop

both objects reach a thermal equilibrium

Temperature

a measure of how hot or cold an object is (how much KE it has)

Thermometer

Particles in substances collide with particles in thermometer before reaching a thermal equilibrium. Liquid in thermometer expands/ contracts as temperature changes to be read

Conduction

The transfer of thermal energy through a substance by the vibrations of particles within the material. its most effective in solids, particularly metals, this occurs through particle movement and movement of free electrons

why are metals good conductors

they have free electrons which can move easily throughout the metal increasing the speed of the transfer of energy

Convection

The transfer of thermal energy in fluids through the mass movement of particles. When a fluid is heated, it expands and becomes less dense, causing it to rise. cooler denser fluid then sinks to take its place, creating convection currents that transfer heat from one region to another

Sea breeze

• land is hotter than the sea druing day

• causes air above the land to become hotter and less dense, rising

• the cool air from the sea is pulled in to replace it

• creating a sea breeze

• at night this is reversed

Radiation

The transfer of thermal energy through electromagnetic waves, specifically infrared radiation. Unlike Conduction and Convection, radiation doesn’t require a medium to travel through and can occur in a vacuum. All objects constantly emit and absorb radiation, hotter objects more than cool

Emitters

give off or release something

larger object = more thermal radiation emitted

Black + Matt

Absorption

absorbing (take in) thermal radiation

black + Matt

white colours

means less thermal energy is lost to surroundings

Thermos flask (Vacuum)

conduction - vacuum means that conduction can’t occur since it requires on particles colliding

Convection - having no gaps (air-tight) means there is no where for the thermal energy to escape via convection

Radiation - Silver wall keeps reflects the thermal energy back inside and keeps cooler air out reflecting it

Increasing thermal energy via radiation

surround in foil - reflects thermal radiation back to reduce heat and reflects thermal radiation back inside trapping the heat

Roof insulation

Layers of fibreglass or similar containing pockets of trapped air

Convection - trapped air can’t move

conduction - air = poor conductor

Double/triple glazing

creates an air gap between 2 plates

Convection - trapped air can’t move

conduction - air = poor conductor

Draught excluders

Insulator placed across the bottom of doors to keep heat in the room

Convection - trapped air can’t move

conduction - air = poor conductor

carpets and curtains

both insulators which keep heat inside

Convection - reduce heat loss to windows

conduction - air = poor conductor

silver lining on insulation/ foil

reflective layer that reflects thermal radiation back into surroundings

Radiation - reflects radiation back to surroundings