Download 15.1 Energy and Its Forms

15.1 Energy and Its Forms
In an avalanche, a
mass of loose snow,
soil, or rock suddenly
gives way and slides
down the side of a
mountain.
The avalanche
releases a great
amount of energy.
15.1 Energy and Its Forms
Energy and Work
How are energy and work related?
Energy is the ability to do work.
Work is a transfer of energy.
15.1 Energy and Its Forms
Energy and Work
Work and energy are closely related.
• Energy is known by the changes it causes.
• Work is done when a force moves an object
through a distance. Energy is transferred by a
force moving an object through a distance.
• Both work and energy are typically measured in
joules (J).
15.1 Energy and Its Forms
Energy and Work
Energy has different forms.
A. The sun gives off energy in the form of heat and
light.
B. Plants convert sunlight into food.
C. People convert food energy into muscle
movement.
15.1 Energy and Its Forms
Kinetic Energy
The energy of motion is called kinetic energy.
The kinetic energy of any moving object
depends upon its mass and speed.
15.1 Energy and Its Forms
Kinetic Energy
• m = mass in kilograms (kg)
• v = speed or velocity in meters per second (m/s)
15.1 Energy and Its Forms
Kinetic Energy
Calculating Kinetic Energy
A 0.10-kilogram bird is flying at a constant speed
of 8.0 m/s. What is the bird’s kinetic energy?
15.1 Energy and Its Forms
Kinetic Energy
1. A 70.0-kilogram man is walking at a speed of
2.0 m/s. What is his kinetic energy?
15.1 Energy and Its Forms
Kinetic Energy
2. A 1400-kilogram car is moving at a speed of
25 m/s. How much kinetic energy does the car
have?
15.1 Energy and Its Forms
Kinetic Energy
3. A 50.0-kilogram cheetah has a kinetic
energy of 18,000 J. How fast is the cheetah
running? (Hint: Rearrange the equation to solve
for v.)
15.1 Energy and Its Forms
Kinetic Energy
3. A 50.0-kilogram cheetah has a kinetic
energy of 18,000 J. How fast is the cheetah
running?
15.1 Energy and Its Forms
Potential Energy
Potential energy is energy that is stored as a
result of position or shape.
There are two forms of potential energy:
gravitational potential energy and elastic
potential energy.
15.1 Energy and Its Forms
Potential Energy
Gravitational Potential Energy
Potential energy that depends upon an
object’s height is called gravitational
potential energy.
This type of potential energy increases
when an object is raised to a higher level.
15.1 Energy and Its Forms
Potential Energy
This diver has gravitational
potential energy as she stands
at the end of a diving board.
She gained the potential
energy by doing work—by
climbing up the steps to the
diving board.
15.1 Energy and Its Forms
Potential Energy
• m is mass in kilograms (kg)
• g is acceleration due to gravity (9.8 m/s2)
• h = height in meters (m)
15.1 Energy and Its Forms
Potential Energy
Height is measured from the ground or floor or
some other reference level.
Doubling either the mass of the object or its
height doubles its gravitational potential
energy.
15.1 Energy and Its Forms
Potential Energy
What is the potential energy relative to the
water surface of a diver at the top of a 10.0meter-high diving platform. Suppose she has a
mass of 50.0 kilograms.
PE = mgh
= (50.0 kg)(9.8 m/s2)(10.0 m)
= 4900 kg•m2/s2 = 4900 J
15.1 Energy and Its Forms
Potential Energy
Elastic Potential Energy
The potential energy of an object that is
stretched or compressed is known as
elastic potential energy.
Something that is elastic springs back to
its original shape after it is stretched or
compressed.
15.1 Energy and Its Forms
Potential Energy
A compressed bicycle shock absorber and a
wound-up toy robot both have elastic potential
energy.
15.1 Energy and Its Forms
Forms of Energy
What are the major forms of energy?
The major forms of energy are mechanical
energy, thermal energy, chemical energy,
electrical energy, electromagnetic energy,
and nuclear energy.
15.1 Energy and Its Forms
Forms of Energy
All energy can be considered to be one of
three forms:
• kinetic energy,
• potential energy, and
• energy in fields such as those produced by
electromagnetic waves.
Each of these forms of energy can be
converted into other forms of energy.
15.1 Energy and Its Forms
Forms of Energy
Mechanical Energy
The energy associated with the motion and position
of everyday objects is mechanical energy.
Mechanical energy is the sum of an object’s potential
energy and kinetic energy.
Examples are speeding trains, bouncing balls and
runners.
15.1 Energy and Its Forms
Forms of Energy
Thermal Energy
The total potential and kinetic energy of all the
microscopic particles in an object make up its thermal
energy.
When an object’s atoms move faster, its thermal
energy increases, and the object becomes warmer.
Examples are molten metal, volcanoes, the sun and
light bulbs.
Anything that is powered by electricity, gasoline or
natural gas has heat (thermal energy) as a waste
product.
15.1 Energy and Its Forms
Forms of Energy
This molten metal is
extremely hot. It
contains a great deal
of thermal energy.
15.1 Energy and Its Forms
Forms of Energy
Chemical Energy
Chemical energy is the energy stored in chemical
bonds.
When bonds are broken, the released energy can do
work. All chemical compounds, including fuels such
as coal and gasoline, store energy.
Examples include batteries, hand warmers and the
chemical energy stored in wood.
15.1 Energy and Its Forms
Forms of Energy
Electrical Energy
Electrical energy is the energy associated with
electric charges.
Electric charges can exert forces that do work.
Examples are generators, lightning, appliances, and
cell phones.
15.1 Energy and Its Forms
Forms of Energy
Electromagnetic Energy
Electromagnetic energy is a form of energy that
travels through space in the form of waves.
Examples include stars, visible light, x-rays,
microwaves, infrared rays, ultraviolet rays, radio
waves and sound.
15.1 Energy and Its Forms
Forms of Energy
A. Lightning bolts transfer
electric charge.
B. Galaxies are giant
structures in space that
typically contain billions
of stars. The stars give
off enormous amounts
of electromagnetic
energy.
15.1 Energy and Its Forms
Forms of Energy
Nuclear Energy
The nucleus of an atom is held together by
strong and weak nuclear forces, which can
store an enormous amount of potential energy.
• The energy stored in atomic nuclei is known as
nuclear energy.
• Nuclear fission releases energy by splitting nuclei
apart.
• Nuclear fusion releases energy when less
massive nuclei combine to form a more massive
nucleus.
• Examples are the sun and atomic bombs
15.1 Energy and Its Forms
Assessment Questions
1. How are work and energy related?
a.
b.
c.
d.
Energy is the rate of doing work.
Work is a form of energy.
Work is the transfer of energy.
Energy is created by work.
15.1 Energy and Its Forms
Assessment Questions
1. How are work and energy related?
a.
b.
c.
d.
Energy is the rate of doing work.
Work is a form of energy.
Work is the transfer of energy.
Energy is created by work.
ANS: C
15.1 Energy and Its Forms
Assessment Questions
2. A moving object with a mass of 10 kg has 320 J of
kinetic energy due to its motion. How fast is the
object moving?
a.
b.
c.
d.
64 m/s
32 m/s
8 m/s
10 m/s
15.1 Energy and Its Forms
Assessment Questions
2. A moving object with a mass of 10 kg has 320 J of
kinetic energy due to its motion. How fast is the
object moving?
a.
b.
c.
d.
64 m/s
32 m/s
8 m/s
10 m/s
ANS:
C
15.1 Energy and Its Forms
Assessment Questions
3. Which of these is an example of elastic potential
energy?
a.
b.
c.
d.
a bow prepared to release an arrow
a rubber ball thrown into the air
a book about to fall from a table
a truck pulling a trailer
15.1 Energy and Its Forms
Assessment Questions
3. Which of these is an example of elastic potential
energy?
a.
b.
c.
d.
a bow prepared to release an arrow
a rubber ball thrown into the air
a book about to fall from a table
a truck pulling a trailer
ANS: A
15.1 Energy and Its Forms
Assessment Questions
4. A small airplane and a helicopter have identical
masses. If the airplane’s altitude compared to the
ground is three times that of the helicopter, how
much more gravitational potential energy does the
airplane have than the helicopter?
a.
b.
c.
d.
0.333 times as much
3 times as much
6 times as much
9 times as much
15.1 Energy and Its Forms
Assessment Questions
4. A small airplane and a helicopter have identical
masses. If the airplane’s altitude compared to the
ground is three times that of the helicopter, how
much more gravitational potential energy does the
airplane have than the helicopter?
a.
b.
c.
d.
0.333 times as much
3 times as much
6 times as much
9 times as much
ANS: B
15.1 Energy and Its Forms
Assessment Questions
5. The energy stored in the bonds between atoms of
a compound is called
a.
b.
c.
d.
electromagnetic energy.
chemical energy.
atomic energy.
thermal energy.
15.1 Energy and Its Forms
Assessment Questions
5. The energy stored in the bonds between atoms of
a compound is called
a.
b.
c.
d.
electromagnetic energy.
chemical energy.
atomic energy.
thermal energy.
ANS: B