Transcript Energy, Heat and Temperature What is energy?

Energy, Heat and Temperature
What is energy?
• The ability to do work (if the work is
done, energy is used)
• Energy is transferred from one object to
another when work is done.
What unit is used to measure
energy?
• Joule
What is potential energy?
• (energy of position)
• The stored energy
resulting from the
relative positions of
objects in a system
What is gravitational potential
energy?
• Potential energy depends on an objects
height above the ground
• Depends on mass and height (mass and
height are directly proportional to gpe)
• GPE = mgh
• Gravitational potential energy =
(mass)(gravitational
acceleration)(height)
What is kinetic energy?
• The energy of a moving
object due to its motion
• Depends on mass and
velocity (mass and
velocity are directly
proportional to ke)
• KE = ½mv2
• Kinetic energy =
½(mass)(velocity)2
Which of the two factors, mass
or velocity, will have a greater
effect on kinetic energy?
• Velocity, because it is squared
KE = ½mv2
What is the law of conservation
of energy?
• Energy cannot be created or destroyed (it’s
just converted from one form to another)
What is an example of a kineticpotential energy conversion?
• As an object falls, its
potential energy
decreases and its
kinetic energy increases
but the total energy
(mechanical energy)
remains the same
What are some other forms of
energy?
a) Heat energy – caused by the internal motion
of atoms
Ex. Friction generates heat energy *causes
changes in temperature and phase of matter
b) Chemical energy – caused by the
breaking/forming of bonds between
atoms
Ex: burning releases chemical energy
as heat energy, when you digest your
food chemical energy is released
c) electromagnetic energy – energy
associated with moving charges
*there are many kinds of
electromagnetic energy: electricity,
light, x-rays, radiowaves, etc.
• d) nuclear energy – caused by changes
in the nucleus of an atom (fission or
fusion)
Fission Reactor
TEMPERATURE AND HEAT
What is heat?
• A form of energy caused by the internal
motion of molecules of matter
How can heat be transferred from
one object to another?
•
The heat always moves from the warmer
object to the cooler object
•
•
•
Conduction
Convection
Radiation
Conduction
• Conduction – heat is transferred
through a substance, or from one
substance to another by the direct
contact of molecules
• Can take place in solids, liquids, and
gases (best in solids)
• Remember: insulators and conductors
Convection
• Convection – heat energy is transferred
through liquids and gases by means of
up and down movements called
convection currents
Radiation
• Radiation – transfer of heat energy
through empty space (does not require
a medium in order to travel) – it is
transferred by electromagnetic waves
• Ex: sun’s heat (infrared radiation), heat
given off by an electric heater or fire
What is temperature?
• A measure of the average kinetic
energy of molecules
• If heat is added to an object, the average
kinetic energy of its molecules increases
and therefore its temperature increases
How are heat and temperature
different?
• Heat depends on the mass of the
substance present
• Ex: 10g of water at 90°C has more heat
energy than 5g of water at 90°C
• Heat is a measure of the actual amount
of energy present where temperature is
a measure of the average amount of
energy present
How is temperature measured?
• With a thermometer; it consists of a thin
tube filled with mercury or colored
alcohol and as the liquid is heated it
expands and rises and when it is cooled
it contracts and falls
What unit is used to measure
temperature?
• Celsius (metric)
• Kelvin (metric)
• Fahrenheit (standard)
What unit is used to measure
heat?
• Calorie or Joule
The food calorie is used to measure how
much energy you get from various foods.
One Calorie is equivalent to about 4,180 J.
What is specific heat?
• Refers to the ability of a substance to
absorb heat energy, some absorb heat
energy easily (conductors) and have a
low specific heat while some do not
absorb heat easily (insulators) and have
a high specific heat
• The specific heat of water 1cal/g·°C
(water has a high specific heat – it requires
a lot of heat to change its temperature)