Download Energy and Heat

Energy and Heat
What is Energy?
• When something is able to
change its environment or itself,
it has energy
• Energy is the ability to change
• Energy has several different
forms, such as electrical,
chemical, mechanical, light,
nuclear, and thermal
Energy Forms
Kinetic Energy
• Kinetic energy is energy in the form of
motion
• The amount of kinetic energy depends on
the mass and velocity of the object
• The kinetic energy of an object can be
calculated using the following relationship:
•
Kinetic energy = ½ mass X velocity2
•
KE = ½ m X v2
• The joule is the SI unit of energy
Kinetic Energy
Potential Energy
• Potential energy is stored energy
• The amount of potential energy depends on its
position or its condition
• Potential Energy can be calculated using the
following equation:
•
Potential Energy = weight X height
•
Weight = mass X Gravity (9.8 m/s2)
• PE is measured in joules
• Elastic potential energy is energy stored by
something that can stretch or compress, such as
a rubber band or spring
• Energy can be stored in the chemical bonds
between atoms
• Energy stored in chemical bonds is chemical
potential energy
Potential Energy
Conservation of Energy
• Energy may change from one
form or another, but the total
amount of energy remains
constant
• Energy cannot be created nor
destroyed
• This statement is known as the
law of conservation of energy
Energy Forms
• Energy can change from one
form to another
• Energy can be found in the form
of: nuclear
mechanical
chemical
thermal
light
electrical
Energy Conversion in a
Car
Energy Conversion in a
Coal Plant
Temperature
• Temperature is the measure of the
average kinetic energy of the
particles in a sample of matter.
• In SI units, temperature is measured
in Kelvin (K) (273 + °C).
• A change in state due to
temperature involves a transfer of
• energy from a warm/hot object to a
cool/cold object.
Thermal Energy
• Like temperature, thermal energy is
related to the energy of the particles that
make up matter.
• Thermal energy is the total energy of the
particles in a material.
• This includes both kinetic and potential
energy.
• Thermal energy of an object increases as
its temperature increases.
• The more mass a material has at the
same temperature, the
• more thermal energy it has.
Heat
• Heat is the thermal (or internal)
energy that flows from something
with a higher temperature to
something with a lower
temperature.
• Heat is a form of energy, so it is
measured in joules
• In most cases, heat flows from
warmer to cooler materials.
Specific Heat
• Different materials need different
amounts of heat to produce similar
changes in their temperatures.
• The specific heat (C ) of a material is
the amount of energy it takes to
raise the temperature of 1 kg of the
material 1 kelvin.
• Specific heat is measured in joules
per kilogram kelvin [J/(kgK)].
Change in Thermal
Energy
• Change in thermal energy = mass X
change in temperature X specific
heat
or Q = m X ΔT X C
• When ΔT is positive, Q is also
positive; the object has
increased in temperature and gained
thermal energy.
• When ΔT is negative, Q is also
negative; the object has lost thermal
energy and decreased temperature.
Movement of Thermal
Energy
• Conduction is the transfer of energy through matter by
direct contact of particles.
• Conduction takes place in solids, liquids, and gases.
• The most important way thermal energy is transferred in
fluids is by convection.
• Convection is the transfer of energy by the bulk
movement of matter.
• In conduction, energy moves from particle to particle, but
the particles themselves remain approximately in place.
• In convection, fluid particles move from one location to
another, carrying energy with them.
• Radiation is the transfer of energy in the form of waves.
• Good insulators do not allow heat to move easily through
them.
Movement of Thermal
Energy
Forced-Air System
• The most common type of heating system
in use today is the forced-air system.
• In this system, fuel is burned in a furnace
and heats a volume of air.
• A fan then blows the warm air through a
series of large pipes called ducts.
• The ducts lead to openings called vents in
each room.
• Cool air returns through the furnace
through additional vents, where it is
reheated.
Forced Air System
Radiators and Electrical
Heating Systems
• A radiator is a closed metal container that
contains hot water or steam.
• The thermal energy contained in the hot water
or steam is transferred to the air surrounding
the radiator by conduction.
• This warm air then moves through the room by
convection.
• An electrical heating system has no central
furnace as forced-air and radiator systems do.
• Instead, it uses electrically heated coils placed
in ceilings and floors to heat the surrounding air
by conduction.
• Convection then distributes the heated air
through the room.
Radiators and Electrical
Heating Systems
Using Heat to Do Work
• Combustion is the process of converting chemical energy
to thermal energy.
• During combustion, a fuel combines with oxygen and
produces heat and light.
• The thermal energy that is produced is then converted
into mechanical energy.
• An engine that converts thermal energy into mechanical
energy is called a heat engine.
• A heat engine is called an internal combustion engine
because fuel is burned inside the engine in chambers, or
cylinders.
• A heat mover is a device that removes thermal energy
from one location and transfers it to another location at a
different temperature.
• Refrigerators, air conditioners, and heat pumps are
examples of heat movers.
Heat Engine
Heat Movers