Unit 4 - Energy and Society Flashcards
(35 cards)
Energy and work
energy = the ability to do work work = the transfer of energy
Types of kinetic energy
heat/thermal = energy of vibrating particles sound = energy transferred by particle motion kinetic = energy of motion
Types of potential energy
gravitational = energy stored in an object due to its height in an area where the force of gravity can act on it to make it fall elastic = energy stored by the bending/stretching or compressing of matter chemical = energy stored in the chemical bonds of matter and can be released by way of a chemical reaction electric = energy stored when static electric charges are held a certain distance apart magnetic = energy stored in the space between two magnets radiant = energy that is carried by electromagnetic waves nuclear = energy stored in an atom’s nucleus that is waiting to be released in a nuclear reaction
Work
work can be done on an object by applying a force that moves it a certain distance
symbol = W
unit = Joules (J)
it is a scalar quantity
the applied force is used to calculate the work done (when = 0) not the net force
Cases when no work is done
the applied force is perpendicular to the displacement
when the displacement is 0
when there is no force
Kinetic energy
the energy possessed by an object because of its motion
unit = Joules (J)
the kinetic energy an object has acquired is equal to the work done to accelerate it
Gravitational energy
the energy possessed by an object because of its height above the ground
if an object is lowered, the change in gravitational energy is negative
the zero height must be specified
the change in height is always measured vertically, and the route taken is irrelevant
Law of conservation of energy
energy can only be transferred from one place to another or transformed from one form to another, it can’t be created or destroyed
in a real system, kinetic and gravitational energy are converted into other forms, most commonly heat and sound
the ultimate “end” of all energy is to become heat, which is then radiated into outer space
Energy efficiency
a measure of the completeness of energy transfer
it measures how much of the energy going into a device is actually transformed to the desired type of energy
energy out = amount of desired energy produced
energy in = amount of energy that goes into the system
Power
the rate at which work is done and at which energy is transformed
symbol = P
unit = Watts (W) which is equivalent to Joules per second
kWh = unit for energy
Kinetic molecular theory
all matter is made of atoms, which group into molecules
these atoms and molecules exert forces on one another that keep them a certain distance apart
the distances between molecules is responsible for the 3 states of matter
Thermal energy
heat/thermal energy = energy of motion, or the kinetic energy of matter at the atomic and molecular level
temperature = way to measure the average kinetic energy of all of the particles in a quantity of matter
thermometer = device for measuring temperature, operates according to thermal expansion
Units of measurement of temperature
Celsius = water freezes at 0 degrees, water boils at 100 degrees Kelvin = water freezes at 273 K, water boils at 373 K, 0 Kelvin is absolute zero, the lowest possible temperature when all molecular motion stops
Heat pumps
use the heat available outside of the house and transfer it inside, reducing the amount of energy needed to heat the house
circulate a substance called a refrigerant through an evaporation and condensation cycle
in the evaporation cycle, it is evaporated at low pressure and absorbs heat from its surroundings
in the condensation cycle, it is compressed at high pressure and releases the heat gained earlier
Methods of heat transfer
conduction = process of transferring heat by particle collisions
metals are good heat conductors because their atoms have mobile electrons which transfer the heat energy
convection = process of transferring heat by a circulating flow of fluid
radiation = process of transferring energy (including heat) by electromagnetic waves, travels at the speed of light, can travel through a vacuum
when radiant energy is absorbed by matter, the particles in the matter increase their vibration, raising the temperature
black particles absorb the most radiation
Specific heat capacity
heat transfer to any substance depends on =
change in temperature = more heat flows if the temperature difference is greater
mass = the more mass there is, the more particles there are to absorb/release energy
type of substance = depends on the intermolecular forces
specific heat capacity = the amount of heat energy to raise the temperature of 1.00kg substance by 1 degree Celsius, it is specific to each substance = J/kgC
High vs low specific heat capacity
high specific heat capacity = requires more energy to increase its temperature and will cool down at a slower rate (Pyrex therefore can keep food warm)
low specific heat capacity = requires less energy to increase or decrease temperature (Mercury can therefore go through thermal expansion faster and can be used in thermometers)
Heat exchange
in every energy transfer, the total amount of energy must remain constant
in a closed system, the total amount of heat lost by one object is equal to the total amount of heat gained by its surroundings
heat transfer stops when the two substances are the same temperature
Thermal expansion
substances expand when heated because their particles vibrate faster
thermal expansion can provide a means of measuring temperature
change in length varies directly as the change in temperature and the original length
coefficient of linear expansion = constant which depends on substance, C-1
Changes of state
the transfer of heat to or from a substance doesn’t always change its temperature
it may cause a change of state instead
temperature remains constant during changes of state, as the heat energy is all used to break or weaken intermolecular/interatomic bonds
latent heat of fusion = the amount of energy required to melt 1 kg of a substance
latent heat of vaporization = the energy required to evaporate 1 kg of a substance
unit = J/kg
Standard notation for nuclear energy
atomic number = number of protons in a nucleus = Z
atomic mass = number of protons and neutrons in a nucleus = A
element symbol = X
Nuclear energy
isotopes = atoms of the same element with different numbers of neutrons
they undergo the same chemical reactions as other isotopes of the same element
their physical properties may differ especially density, melting point, and boiling point
some may be radioactive
Radioactivity
radioactivity = the release of energy as a result of the disintegration of the nucleus
ionizing radiation = particles or waves of energy that carry enough energy to remove an electron from an atom
may damage DNA and includes UV light, X-rays, and the three types of radioactivity
photon = unit of electromagnetic radiation
natural transmutation = the formation of a new element through the three types of radioactivity
Three types of radioactivity
alpha decay = an alpha particle (helium nucleus with 2 protons and 2 neutrons) is emitted, discovered by Marie Curie, penetrates a few cells
beta decay = the emission of an extremely high energy electron, the electron is created when a neutron is converted into a proton and an electron, penetrates a few sheets of aluminum
gamma ray emission and electron capture = a gamma ray is extremely high energy electromagnetic radiation, the nucleus captures an electron and it combines with a proton to form a neutron, penetrates few cm of lead or 2 km of air
