physics
Heat- the transfer of thermal energy from a hotter to cooler object.
cannot transfer from cold to hot without work being done.
heat is measured in joules
Thermal energy transfer- collisions of particles, heat moves from warm skin to the cooler thermometer.
Heat absorption- when an object absorbs thermal energy, the value of heat (Q) is positive
Heat loss- when an object loses thermal energy, the value of heat (Q) is negative
conduction is the transfer of thermal energy through direct contact between particles in a solid from hotter to cooler ones.
example- metal rod heated at one end in a flame.
- spoon in hot water.
convection is the transfer of thermal energy in liquids or gases through the motion of fluid. the heated fluid rise while cooler fluid sinks creating a circulation.
example- water heating in a pot
-atmospheric convection (thunderstorms, hurricanes)
radiation is the transfer of energy through electromagnetic waves which do not require a medium(no need for matter) - energy is transferred through space or air as light and heat waves. can occur in vacuum
example- the sun warming the earth, heat felt from a fire or light bulb.
specific heat is the amount of energy that must be added to a unit mass of a material to raise its temperature by one temperature unit
specific heat is measured in joules per kilogram per degree celsius (j/kg.k)
-specific heat common materials- metals(used for cooking pans) have low specific heats and are good thermal conductors.
-water has a high specific heat, meaning it heats up slowly and retains heat longer. this property of water influences climate and helps regulate body temperature.
-ice and water vapor also have high specific heat.
~low specific heat like metals heat up faster
~high specific heat like water take longer to heat up
specific heat formula: Ca= -Mb Cb Tb/MaTa
final temperature formula: Tf= MaCaTa+MbCbTb/MaCa+MbCb
calorimeter- is a device used to measure changes in thermal energy.
it is carefully insulated to minimize energy transfer to the external environment.
as thermal energy is transferred from the hot substance to the cold water, they eventually reach an equilibrium temperature.
the change in thermal energy of the hot substance and the water is related by energy conservation in a closed system.
energy conservation: energy cannot enter or leave the system but can be transferred between the hot substance and the water.
energy change sign in convention:
positive energy changes indicates a rise in temperature
negative energy changes indicates a fall in temperature
types of collisions
elastic collisions : kinetic energy and momentum conservation is conserved
example- steel balls or hard plastic collisions
inelastic collision : kinetic energy decreases and momentum conservation is conserved
example- clay or soft material collisions
perfectly inelastic collisions : kinetic energy decreases and momentum conservation is conserved
example- car crashes where vehicles stick
superelastic collision : kinetic energy increases and momentum conservation is conserved
example- explosive events or spring system