Transcript Energy and Its Forms

Energy and Its Forms
15.1 pg 446-452
Energy and Work
 Energy
is the ability to do work
– Energy is transferred by a force
moving an object through a
distance
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 Work
–
is a transfer of energy
When work is done on a n object,
energy is transferred to that object
Example of work and energy:
Carrying your backpack up stairs
Lift it -- AGAINST the force of gravity
 REQUIRES energy from your MUSCLES
 Muscles REQUIRE energy from FOOD
 Food REQURIES energy from plants and
other animals.

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Kinetic Energy (KE)
 Is
the energy of motion
– Depends on an objects velocity
(speed) and mass
 The kinetic energy of any moving
object depends upon its mass and
speed
 Kinetic Energy (KE) = 1/2 m x v2
– Where m = mass in kg and v =
velocity in m/s
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Sample Problem for KE:

A 0.1 kg bird is flying at a constant speed of 8
m/s. What is the bird’s kinetic energy?
–
Given info:


–
Step 1:

–
KE = 1/2 mv2
Step 2:

–
Mass = 0.1 kg
Speed or v = 8 m/s
KE = 1/2 (0.1 kg) (8 m/s)2
Step 3:
KE = 3.2 kgm2/sec2
= 3.2 kgm/sec2 m
And because kgm/sec2 is a Newton we can write…
KE = 3.2 Nm
And Nm is a Joule
so finally…KE = 3.2 Joules

Potential Energy (PE)

Energy that is stored because of position or
shape
– A stretched string on a guitar or a streched
rubber band has potential energy (PE)
 Two types of PE:
– Gravitational Potential Energy
– Elastic Potential Energy
Gravitational Potential
Energy(GPE)
Potential energy that depends upon an
object’s height
 An objects GPE depends on its mass, its
height, and acceleration due to gravity
 Increases when an object is raised to a
higher level
 GPE or PE = mgh

–
Where m is mass, g is gravity, and h is height
Sample Problem for PE

A 50 kg diver is at the top of a 10 meter high diving
platform. What is the diver’s potential energy?
–
Given info:



–
Step 1:

–
PE = mgh
Step 2:

–
Mass = 50 kg
Height = 10 m
Gravity = 9.8 m/sec2
PE = 50 kg (9.8m/sec2)(10m)
Step 3:
PE = 4900 kgm/sec2 m
And because kgm/sec2 is a Newton we can write…
PE = 4900 Nm
And Nm is a Joule
so finally…PE = 4900 Joules

Elastic Potential Energy (EPE)


The potential energy of an object that
is stretched or compressed
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Examples
–
Stretched
 Ukulele
–
string, rubber band, etc.
Compressed
 Bouncing
a ball, shocks on a car, etc.
Forms of Energy
1.
2.
3.
4.
5.
6.
Mechanical:
– Both Kinetic and Potential
together
Thermal
Chemical
Electrical
Electromagnetic
Nuclear
Mechanical Energy (ME)
The energy associated with the motion
and position of everyday objects
 Sum of an objects Potential and Kinetic
Energy
 Does not include thermal, chemical or
other forms of energy associated with
the motion or arrangement of atoms or
molecules
 ME = PE + KE

Thermal Energy
Atoms
in an object are
always in motion
The total PE and KE of the
molecules make up its
thermal energy
Faster motion, more thermal
energy
Chemical Energy
 Chemical
Energy is the energy
stored in chemical bonds.
– When broken they release
energy
– All chemical compounds store
energy
 Gives energy from food
 Warm from firewood
 Energy from coal
Electrical Energy
Energy
associated with
electric charges
– Batteries convert chemical
energy into electric
– Lightning bolts
Electromagnetic Energy
 Electromagnetic
energy is a
form that travels through space
in the form of waves
– Visible light
– X rays
– Gamma Rays
– Microwaves
Nuclear Energy
The
energy that is stored in
atomic nucleus
– Nuclear power plants fission - release energy
– The sun - Fusion - release
energy when nuclei
combine
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