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Energy
Forms of Energy
Energy is the ability or capacity of any
physical system to do work
 Work is done by forces
 Kinetic Energy – energy in motion
 Potential Energy – energy at rest or
stored energy
 Any form of energy can be converted
into another form

Types of Energy
Thermal – a.k.a. heat energy
 Electrical – from forces of the electrical
charges of subatomic particles (p & e)
 Light – radiant energy (makes up the
electromagnetic spectrum)
 Nuclear – stored in the bonds of an
atom’s nucleus (given off by breaking or
creating those bonds)

Transformation
Changing one form of energy into
another
 Ex: Hydroelectric dams use generators
to transform the kinetic mechanical
energy of falling water into kinetic
electrical energy

Law of Conservation of Energy
Energy is neither created nor destroyed,
it is changed from one form to another
 In a closed system, the amount of
energy remains constant. (Ex: the cells
in your body)
 In an open systems, energy is lost to
heat and other transformations.
 Explained by James Prescott Joule

Chemical & Mechanical
Chemical potential energy is stored in
the nutrients in food – your cells
transform it into kinetic energy
 Some of this energy is changed into
mechanical energy (Ex: when your
brain sends a signal to move your
muscle)
 Changes into Mechanical Energy

When you speak – mechanical
energy in your breath is
changed into sound energy by
your vocal chords
 Nerve cells transform chemical energy
into electrical energy that transmits
nerve signals to parts of the body
 When you eat, chemical energy from
food is turned into thermal energy (heat
energy)

Other animals do this too…
Electric eels – use electrical
energy to stun their prey or
keep predators away with
powerful shocks
 Fireflies – transform chemical
energy into light energy

Other uses…
Thermal energy keeps us warm
when its cold outside
 When a match is struck, friction
transforms mechanical energy into
enough thermal energy to ignite the
match
 Chemical energy stored in the wood of
the matchstick changes into more
thermal energy as the wood burns

Mass related to energy…
The more mass an object has, the more
energy it can absorb
 Ex: The ocean’s huge mass absorbs a
tremendous amount of heat during the
summer & releases it during the winter
– this helps keep coastal
climates more moderate
during both seasons

Lava lamps…
Transform electrical energy into light
energy, mechanical energy, and
thermal energy.
 These transformations happen
all day every day, in our bodies
and all around us

Mechanical Energy…2 parts
Kinetic energy
 Potential energy
 ME = KE + PE

Kinetic Energy
Energy in motion
 KE = ½ m v2
 KE = ½ • mass • velocity2

Figure it out…
What is the K.E. of a 10 kg mass
moving w/ a velocity of 10 m/s?
 KE=½ mv2
 KE=½ (10 kg) (10 m/s)2
 KE=500 kg•m2/s2
 1 kg•m2/s2 =1 J
 KE=500 J
 What if you double the mass?
 What if you double the velocity?

(5000 J)
(2000 J)
Potential Energy
Energy at rest = potential to move
 PEg = m g h
 g = gravitational acceleration = ?
 PEg = mass • 9.8 m/s2 • height
 Always measured in reference to the
height
 Different types of potential energy
 Involves mass, gravity, & height

Figure it out…
What is the PE of a 10 kg rock on top of
a 100 m hill?
 PEg = m g h
 PEg = (10 kg) (9.8 m/s2) (100 m)
 PEg = 9800 kg • m/s2 • m
 PEg = 9800 J

Reminder
ME = KE + PE
 N = kg • m/s2
J=N•m
 Acceleration due to Gravity = 9.8 m/s2


Ch 14 & 15 Review
Work, Power, Energy
Formulas
W=F•x
P=W/t
 PEg = m g h
 KE = ½ m v2


Facts
IMA vs. AMA
 Why?
 Newton’s laws of motion
 1st
 2nd
 3rd

