2. The Nature of Energy
What is energy?
Energy is the ability to
cause a change or Mechanical
the ability to do work
Electrical Energy
Energy
What Solar Energy
are the different
forms of energy?
Heat Energy
Nuclear Energy
3. The energy of different objects may fall into
two main categories:
Kinetic Energy and Potential Energy
Kinetic Energy is the energy of a moving
object
Potential Energy is stored energy. This
can be thought of in two ways. Stored
energy in our bodies or in a battery is called
chemical potential energy. Stored energy
energy
due to the position of an object above the
surface of the earth is gravitational
potential energy.
4. Calculating Kinetic Energy
Kinetic Energy depends upon two factors: the mass of
the object and its velocity.
Mass is measured in kg and velocity is measured in m/s
When the units are multiplied, the result is kg m2/s2
Since a Newton (N) is a kg m/s2, therefore kg m2/s2 is
the same as a N-m, which is the same as a joule (J).
Hence, the unit of kinetic energy is the joule.
5. Practice Problems
How much energy does a soccer player with a
mass of 75 kg and a velocity of 5.5 m/s possess?
KE = ½mv2 KE = ½(75 kg)(5.5 m/s)2
KE = 1.1 X 103 kgm2/s2 1 kgm/s2 = 1N
KE = 1.1 X 103 Nm 1 Nm = 1 Joule (J)
KE = 1.1 X 103 Joules (J)
6. Solve the following:
What is the velocity of a car with a mass of 675
kg and a kinetic energy of 1690 joules?
2(KE)=2( ) 2KE = mv
½mv 2 2 2KE = v2
m
2KE = v v= 2(1690J)
m 675 kg
v = 2.24 m/s
7. Calculating Gravitational Potential Energy
Gravitational Potential Energy (GPE) depends upon
three factors: the mass of the object, the height of the
object from the surface of the earth, and the gravitational
acceleration constant (on earth = 9.8 m/s2)
Notice how the units multiply :
mass (kg) x m/s2 x height (m). Hence the unit is kg m2/s2
which is the joule (J).
Let’s do a practice problem…
8. Potential Energy
Calculate the energy possessed by a rock on
the side of a cliff. The rock has a mass of 237
kg at an elevation of 45 meters.
PE = mgh PE = (237 kg)(9.8 m/s2)(45m)
PE = 1.0 X 105 kgm2/s2
PE = 1.0 X 105 Nm
PE = 1.0 X 105 Joules
9. What is the Law of Conservation of Energy?
Energy
Energy cannot be created nor destroyed….but….
Energy can be transformed from one type to
another.
In this diagram, electrical
energy is converted into
thermal (heat) energy
and light energy.
10. There are many energy transformations in an
automobile.
The explosion of the gasoline involves the
release of chemical energy.
The chemical energy causes the pistons in
the engine to move (mechanical energy)
The moving pistons affect many moving parts
including a generator which produces
electrical energy which keeps the battery
charged.
The moving pistons and other moving parts
also produce heat energy.
11. Objects can convert potential energy to kinetic
energy or kinetic energy to potential energy.
The diagram below illustrates this relationship.
13. The major source of energy is the SUN.
In photosynthesis plants convert sunlight into
stored energy in the plants.
Animals and humans eat the plants to get
energy.
The human body “burns” this stored energy in
units called Calories.
One Calorie is equal to 4.18 J.
The human body stores energy in Calories and
will utilize “burn” this energy as needed.
15. Particles of matter are in constant motion. This
motion relates directly to the state of matter of the
object (solids, liquids, or gases).
Temperature affects how fast these particles
move. The higher the temperature the faster the
particles move. Moving particles possess kinetic
energy.
Temperature is defined at the average kinetic
energy of the particles of an object.
16. Thermal Energy is the sum total of all of the
energy of the particles of an object.
Thermal energy and temperature are related
though DIFFERENT.
Temperature is the average kinetic energy of the
particles of an object.
Thermal energy is the total amount of energy of
the particles of an object.
A bathtub full of water at 100oF has more thermal
energy than a thimble of water at 100oF. The
temperature is the same but the total amount of
energy is different. The bathtub has more energy.
17. What is heat?
heat
Heat is thermal energy that flows from
something at a higher temperature to
something at a lower temperature.
What is specific heat?
heat
Specific heat is a property of matter which
determines how readily a material is to absorb
heat and change temperature.
Specific Heat is defined as the amount of heat
energy needed to raise the temperature of 1
kg of a substance by 1 oC or 1 K.
18. Did you notice that water has a very high specific
heat, whereas iron has a low specific heat?
Water requires a lot of heat energy to raise its
temperature.
19. Metals require little energy to raise its
temperature.
Thermal energy can be calculated using the
following formula:
20. Try this one!! Answer = 376 J/kg K
Did you do this problem?
21. Transferring Thermal Energy
How is Thermal Energy Transferred? YOU MUST
KNOW THIS!!!!!
Conduction – direct contact
Convection – through a fluid
Radiation – by electromagnetic waves
22. What is heat transfer by conduction?
conduction
Heat transfers as particles of an object increase
their collisions as heated. These collisions
transfer the heat energy through the object by
colliding with adjacent particles.
23. What is heat transfer by convection?
convection
Heat is transferred through a substance through
currents. This occurs in fluids (liquids AND
gases)
Convection currents are caused by heating of a
liquid or gas, the liquid or gas rises, then cools
and falls. This occurs in the mantle of the earth
And in the atmosphere.
Most of our weather patterns are the result of
convection currents in the atmosphere.
24. What is heat transfer by radiation?
Radiation is heat transfer by electromagnetic
waves. These wave may pass through all states
of matter and also through NO matter – such as
the vacuum of space.
This energy is often called radiant energy.
Radiant energy from the sun travels through the
vacuum of until it reaches the earth.
25. How is heat flow controlled?
Insulators – a material which does not allow heat
to pass through it easily. Some animals have
good insulation to
survive severe winters.
26. Buildings and houses are insulated so that heat
does not pass out of (winter time) and into
(summer time).
28. Using heat – How do we use heat in our lives?
Forced-Air Systems – a fuel is burned in a
furnace and a fan circulates the heat in the house
29. Radiator Systems – closed metal containers that
contain hot water or steam. The thermal heat is
transferred to the air and circulated by convection
currents.
Electric radiators – heat metal coils which
transfer the thermal heat to the surrounding air.
30. Automobile engines are usually four-stroke
engines since each four-stroke cycle converts
chemical/thermal energy to mechanical energy.
31. Refrigerators, air conditioners, and heat pumps –
how do they work?
A coolant is circulated through pipes by a
compressor. When the pipes get small and
narrow the coolant compresses and changes to a
liquid giving off heat energy. When the pipes get
larger, the coolant changes from a liquid to a gas
(evaporates) causing the area to absorb heat and
get cooler
32. The human coolant - In-built cooling system
The human body has a cooling system which
function automatically – perspiration – sweat.
Like a refrigeration
system, the evaporation
of the sweat from the
surface of the body
causes energy to be
absorbed from the skin,
causing the skin to feel
cooler.
No sweat!!!
