Transcript Thermal Energy - St. Thomas the Apostle School

Thermal Energy
Chapter 6
Describe things you do to make yourself feel
warmer or cooler.
Matter in motion
• The matter around you is made of tiny particlesatoms and molecules
• These particles are in constant motion
• Because they are moving they have kinetic energy
• The faster they move the more kinetic energy they
have
• These particles move faster in hot objects then cooler
objects.
Temperature and Heat
• Temperature- related to the average kinetic energy of an objects
atom’s or molecules.
• Thermal Energy- the sum of the kinetic and potential energy of all the
atoms in an object.
-thermal energy increases as temperature increases.
-At constant temperature, thermal energy increases if mass
increases
Thermal energy that flows from something at a higher temperature to
something at a lower temperature is called HEAT.
• Specific Heat- amount of heat needed to raise the temperature of 1kg
of a material by 1 degree C or K.
Changes in thermal energy can be calculated as change in thermal
energy equals mass times change in temperature times specific heat.
1. When heat flows into an object and its temperature rises, the
change in temperature is positive.
2. When heat flows out of an object and its temperature decreases,
the change in temperature is negative.
3. A calorimeter is used to measure specific heat.
Actions that increase
thermal energy
Explanation
• Raise the temperature of an
object
• Increases the kinetic energy of
the atoms or molecules
• Pull atoms or molecules that
attract one another farther
apart
• Increases the potential energy of
the atoms or molecules
• Add mass to the object, without
changing its temperature
• More molecules at the same
level of energy means more total
energy in the object
Specific heat
Water as a coolant
•Water has the highest specific heat
•Water can absorb heat without a large
change in temperature.
•For example: Water is used as a coolant in
an automobile.
Measuring specific heat
• Can be measured through the use of a calorimeter.
• The mass of the sample is measured, as is the initial temperature of
the water in the calorimeter. The material is then heated,
temperature measured, and the sample is placed in the inner
chamber.
How do temperature and heat differ?
Transferring
Thermal Energy
•Thermal energy is transferred from place to
place by conduction, convection and
radiation.
Conduction- the transfer of thermal energy by
collisions between particles in matter.
Conduction occurs because particles in matter are in
constant motion.
Kinetic energy is transferred as particles collide.
Solids, particularly metals, are good heat conductors
The best conductors of heat are metals.
• Silver and aluminum and copper are the best conductors of heat
Convection- the transfer of energy by the motion
of heated particles in a fluid.
• Convection currents transfer heat from warmer to cooler parts of a
fluid.
• Convection currents create rain forests and deserts over different
regions of Earth.
Radiation- energy transfer by electromagnetic
waves
• Some radiation is absorbed and some is reflected when it strikes a
material.
• Heat transfer by radiation is faster in a gas than in a liquid or solid
Compare and contrast radiation, convection,
and conduction.
Complete the table
How is heat
transferred
definition
Example
How can you control heat flow?
• Humans use clothing, jackets..etc…
• Animals have blubber, thick coats, scaly skin, feathers, color of skin,
etc….
• What are some items you use to control heat
flow?
Insulator- material that does not let heat flow
through it easily
• Gases such as air usually make better insulators than liquids or solids
• A vacuum layer in a thermos is a good insulator because it contains
almost no matter to allow conduction or convection to occur.
Most living things control the flow of heat by using
special features such as fur, feathers, blubber, or
scales
What types of heating systems are used in
your home?
USING HEAT
Heating Systems-Warm homes and buildings
1. Forced air system- fuel heats air, which is blown through ducts
and vents; cool air is returned to the furnace to be reheated.
2. Radiator System- hot water or steam in a radiator transfers
thermal energy to the air
3. Electric Heating System- electrically heated coils in ceilings or
floors heat air by conduction
Solar Energy- energy from the sun
• Passive solar heating does not use mechanical devices to move heat.
(windows in a home)
-Active solar heating use solar collectors to absorb radiant energy,
which is circulated through the building
THERMODYNAMICS
• Thermal energy, heat, and work are related and the study of
their relationship among them.
• Heat and work increase thermal energy
• The first law of thermodynamics- the increase in thermal
energy of a system equals the work done on the system plus
heat transferred to the system.
• Closed system- no energy is added to a system
• Open system- energy is added to a system
• The second law of thermodynamics- heat cannot flow from a
cool object to a warmer object unless work is done
Heat Engine- an engine that converts thermal
energy into mechanical energy
• Internal Combustion Engine- Burns fuel inside the engine in chambers
or cylinders.
• Internal combustion engines convert only 26% of the fuel’s chemical
energy to mechanical energy.
Heat Mover- a device that removes thermal
energy from one location and transfers it to
another location at a different temperature.
• Refrigerator- contains a coolant that absorbs heat from the inside of
the refrigerator and releases it on the outside as heat.
• Air conditioner- Cools warm air
• Heat pump- can both cool and warm air
• The human body stays cool by EVAPORATION of sweat.