Download 15.1 Energy and Its Forms

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.
http://phun.physics.virginia.edu/demos/double.html
15.1 Energy and Its Forms
Energy and Work
Work and energy are closely related.
• Work is done when a force moves an object through a
distance.
• Energy is transferred by a force moving an object
through a distance.
• Work and energy are 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.
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.
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
Forms of Energy
What are the major forms of energy?
1. Mechanical Energy
a. Kinetic
b. Potential
2. Thermal energy
3. Chemical Energy
4. Electrical Energy
5. Electromagnetic Energy
6. Nuclear Energy
15.1 Energy and Its Forms
1. Mechanical Energy
• Energy associated with the motion and position of
objects.
• potential energy + kinetic energy.
15.1 Energy and Its Forms
2. Thermal Energy
The total potential and kinetic
energy of all the microscopic
particles in an object.
If atoms move faster, its
thermal energy increases, and
the object becomes warmer.
15.1 Energy and Its Forms
3. Chemical Energy
Energy stored in chemical bonds.
When bonds are broken, the released energy can do
work. All chemical compounds store energy.
Ex: use the chemical energy
of burning wood to produce
thermal energy for roasting
marshmallows.
15.1 Energy and Its Forms
4. Electrical Energy
Energy associated with electric charges.
15.1 Energy and Its Forms
5. Electromagnetic Energy
A form of energy that travels through space in the
form of waves.
15.1 Energy and Its Forms
5. Electromagnetic Energy
More examples:
A. Lightning bolts
B. Galaxies contain billions of
stars. The stars give off
electromagnetic energy.
15.1 Energy and Its Forms
6.Nuclear Energy
The energy stored in the nucleus of an atom
• Nuclear fission releases
energy by splitting nuclei apart.
• Nuclear fusion releases
energy when nuclei combine.
15.1 Energy and Its Forms
2 Types of Mechanical Energy: Kinetic Energy &
Potential Energy
Kinetic Energy:
The energy of motion is called kinetic energy.
The kinetic energy depends on mass and velocity.
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
What information are you given?
15.1 Energy and Its Forms
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?
Answer:
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?
Answer:
KE = (0.50)(70.0 kg)(2.0 m/s)2 = 140 J
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?
Answer:
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?
Answer:
= (0.50)(1400 kg)(25 m/s)2
= 437,500 J
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.)
Answer:
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.)
Answer:
15.1 Energy and Its Forms
Potential Energy
Energy that is stored as a result of position or shape.
2 types:
1. Potential Energy
2. Gravitational Potential Energy
An object’s gravitational potential energy
depends on its mass, its height, and the
acceleration due to gravity.
15.1 Energy and Its Forms
REVIEW
Major forms of energy
1. Mechanical Energy
a. Kinetic
b. Potential
2. Thermal energy
3. Chemical Energy
4. Electrical Energy
5. Electromagnetic Energy
6. Nuclear Energy
15.1 Energy and Its Forms
REVIEW
Mechanical Energy =
Kinetic Energy + Potential Energy
or
ME = KE + PE
KE is the energy of _____________
motion
15.1 Energy and Its Forms
Potential Energy
Potential Energy: energy stored as a result of position.
2 types of PE:
1. Gravitational PE
2. Elastic PE
15.1 Energy and Its Forms
Question…..
Assuming your mass is
50 kg, would you rather –
1. Fall off a 5 meter tower
on the moon.
Or
2. Fall off a 0.5 meter tall
desk on earth with 20
kg (about 44 lbs) of
rocks in your pockets.
15.1 Energy and Its Forms
Gravitational Potential Energy
PE depends upon an object’s height
As height increases, PE increases.
15.1 Energy and Its Forms
Gravitational Potential Energy
PE depends upon an object’s mass
As mass increases, PE increases.
15.1 Energy and Its Forms
Gravitational Potential Energy
PE depends upon gravity
As gravity increases, PE increases.
15.1 Energy and Its Forms
Summary:
If height increases, then PE increases
If mass increases, then PE increases
If gravity increases, then PE increases
Let’s put it all together in 1 equation!!
15.1 Energy and Its Forms
• Mass = kilograms (kg)
• Height = meters (m)
• Gravity: g = 9.8 m/s2
The unit for gravitational potential energy = joules.
15.1 Energy and Its Forms
Gravitational Potential Energy
1. What is the potential energy of a 50 kilogram diver
at the top of a 10 meter high diving board?
PE = ?
m = 50 kg
g = 9.8 m/s2
h = 10 m
PE = mgh
= (50 kg)(9.8 m/s2)(10 m)
= 4900 kg•m2/s2 = 4900 J
15.1 Energy and Its Forms
2. A car that is to be transported by ship is
raised 7 m above the dock. If its mass is
1000 kg, what is the car’s gravitational
potential energy?
PE = ?
m = 1000 kg
g = 9.8 m/s2
h=7m
PE = mgh
= (1000 kg)(9.8 m/s2)(7 m)
= 68,600 kg•m2/s2 = 68,600 J
15.1 Energy and Its Forms
3. A small airplane and a helicopter have the same mass.
The airplane’s altitude is 3 times higher than 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
Question…..
Assuming your mass is
50 kg, would you rather –
1. Fall off a 5 meter tower
on the moon.
Or
2. Fall off a 0.5 meter tall
desk on earth with 20
kg (about 44 lbs) of
rocks in your pockets.
15.1 Energy and Its Forms
Moon
Earth
PE = ?
m = 50 kg
g = 1.6 m/s2
h=5m
PE = ?
m = 50 kg + 20 kg=70 kg
g = 9.8 m/s2
h = 0.5 m
PE = mgh
PE = mgh
= (50 kg)(1.6 m/s2)(5 m)
= (70 kg)(9.8 m/s2)(0.5 m)
= 400 J
= 343 J
15.1 Energy and Its Forms
Homework
Due Wednesday March 25
15.1 Energy and Its Forms
Potential Energy
When this musician pulls the
string of her cello to one side,
the string is stretched and
gains potential energy.
The stored energy is converted
into kinetic energy when the
string is released and it
vibrates.
15.1 Energy and Its Forms
Elastic Potential Energy
The potential energy of an object that is stretched
or compressed.
Ex: shock absorber, spring, slingshot
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
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