energy, work, heat

definitions:

work → process of energy conversion / transfer

work done → amount of energy converted / used

energy → ability to do work, measured in J - joules

kinetic energy → energy an object possesses by virtue of its motion

potential energy → energy an object possesses by virtue of its position, condition or state

renewable energy → energy that can be replenished naturally

non-renewable energy → energy that cannot be renewed naturally

temperature → measurement of degree of hotness

thermal equilibrium → no net change of thermal energy between two objects - same temperature

conduction → transfer of thermal energy through a medium without any flow of the medium

convention → transfer of thermal energy by means of convection currents in a fluid due to a diff in density

heat insulator → poor conductor of heat

greenhouse effect → process that occurs when greenhouse gases in earth’s atmo trap the sun’s heat, making earth warmer

energy

• defined as the capacity to do work

• SI unit: J (Joules)

• can exist in different forms

principle of conservation of energy → energy cannot be created nor destroyed, can only be converted from one form to another (total amount of energy in a system is constant)

conversion of energy: heat and sound given off due to friction, eg. gpe → ke + heat + sound

work done:

definition of work done → defined as the product of constant force exerted on that body and the distance moved by the body in the direction of the force, measure of how much energy converted

• occurs when force applied causes object to move in the direction of the force

• formula: w = f x d

• SI unit: J

kinetic energy:

• energy a body possesses due to its motion, moving objects

• translational → moving car

• rotational → rotating turbine

• vibrational → atoms and particles

• formula: ke = ½ mv2

• ke is dependent on mass of object and speed

• mass increase, ke increase proportionally

• speed increase, ke increase more than proportionally

gravitational potential energy (GPE)

• energy possessed by body due to its position above ground

• formula: gpe = mgh

• proportionally increases

renewable and non-renewable energy

solar → renewable ; large open spaces needed and toxic waste from solar panels require treatment

hydroelectric → renewable ; affect plants, aquatic life, wildlife → large areas needed are flooded

wind → renewable ; noise pollution, occupies lots of land space, affects birds, not aesthetically pleasing

geothermal → renewable ; wildlife habitats affected

biomass / biofuels → renewable ; air pollution, large emissions of co2 and water vapour, greenhouse gases

fossil fuels → non-renewable ; air pollution, large emissions of co2 and water vapour, greenhouse gases

nuclear → non-renewable ; potential radiation exposure, issues with disposal of depleted fuel rods

heat

heat → form of energy

temperature → measurement of degree of hotness, used measure temperature based on fixed points, related to a body’s KE (higher temp, particles move faster)

heat transfer

• 2 diff temp regions → heat flows from hotter region to cooler region

• same temp → no net flow of heat, thermal equilibrium

processes:

• conduction

  • transfer of heat involves movement of particles

  • transfer of thermal energy through a medium without any flow of the medium

  • conduction in solids

    • when heated → particles at hot end will vibrate more vigorously in fixed positions and collide with neighbouring particles

    • neighbouring particles start to vibrate vigorously as KE is transferred, become hot, process repeat

    • thermal energy transferred without flow of particles

    • metals have high thermal conductivity, other materials and water usually have low conductivity

    • metals have free electrons that can move randomly among the metal atoms, atoms vibrate more vigorously compared to other materials when heated, free electrons also gain KE and move faster, colliding with atoms in cooler region

  • conduction in liquids and gases

    • happen less frequently (collisions) because they are spaced far apart → poor conductors of heat

    • water in boiling tube → ice at bottom and water on top boiling → poor conductor

• convection

  • transfer of thermal energy by means of convection currents in a fluid (liquid or gas), due to a difference in density

  • water at bottom heated → water at bottom expand, less dense than surrounding water, rise to top, cooler water denser so sink, convection current

  • only in liquid and gas cos particle can move freely, not in solids because particles cannot move

insulators of heat → lagging

bimetallic strips → made of two diff metals, with different conductivity, used in thermostats

greenhouse effect

• process that occurs when greenhouse gases in earth’s atmo trap sun’s heat, make earth warmer

• greenhouses gases: water vapour, methane, carbon dioxide

• too much greenhouse gas → global warming

• greenhouse → used to magnify light energy from sun + protect plants from freezing temp

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