Energy &
Work
Energy
is the ability to do work
whenever you do
work, you transfer energy
from one thing to another
energy is measured in units
called joules
Energy can be classified as
Potential or Kinetic
Potential Energy is stored energy (Ep)
~the amount of potential energy
depends on its position
~ Ex: a rock at the edge of a cliff
Kinetic Energy is energy in motion (Ek)
~ the amount of kinetic energy
depends on the mass of the moving
object and its speed
~ Ex: a moving skateboard
Kinetic and Potential Energy
Conversions
Describe the energy
conversions in this picture:
at the top: All PE, no KE
¼ of the way down: 3/4 PE, 1/4 KE
½ way down: 1/2 PE, 1/2 KE
¾ down 1/4 PE, 3/4 KE
at the bottom: No PE, All KE
Types of Potential Energy
Elastic Potential Energy-energy stored by
things that stretch or compress
Chemical Potential Energy-energy stored in
chemical bonds between atoms
Gravitational Potential Energy-energy stored
in things that are above Earth
– The amount of GPE depends on its mass,
the acceleration due to gravity, and its
height above ground
Gravitational
Potential
Energy
The boulder has
more gravitational
potential energy when
measured from
point A compared to B.
What happens
when the cord
is cut?
Potential energy
is converted to
kinetic energy.
Kinetic and Potential energy
convert to one another
PE max
PE max
no KE no KE
KE max KE max
no PE no PE
POTENTIAL
OR
KINETIC
ACTIVITY
Forms of Energy
Electrical
Magnetic
Thermal (Heat)
Nuclear
Chemical
Mechanical
Mechanical Energy
the sum of the potential
energy and kinetic energy
in a system
Em = Ep + Ek
Thermal Energy
is the total energy of the particles in a
material
specific heat can be used to measure changes in
thermal energy
specific heat (Cp) is the amount of energy it
takes to raise the temperature of 1kg of
material 1 degree Kelvin
Thermal Energy
is the total energy of the
particles in a material
specific heat can be used to
measure changes in thermal energy
specific heat (Cp) is the amount of
energy it takes to raise the
temperature of 1kg of material 1
degree Kelvin
Electrical Energy
the energy of charged
particles that can travel
through empty space in
electromagnetic waves
Examples include:
Ultraviolet, X-rays, infrared (or heat),
radio waves, microwaves, and radar
Nuclear Energy
energy from changing the nucleus
of atoms
Can be either:
Fusion–two nuclei are fused together
(takes place in the sun)
Or
Fission-two nuclei are broken apart
Nuclear energy- clean power for
the world?
Law of Conservation
of Energy
energy can’t be
created or destroyed
the total energy
remains constant
it just changes form
How is mass related to energy?
Albert gave us
the answer!
E=mc2
Think you can design
your own roller
coaster?
Lets give it a try!!
http://www.learner.org/interactives/parkphysics/coaster.html
http://www.harcourtschool.com/activity/electromagnets/
Work
Work
When an Olympic weight lifter
presses a barbell over his
head,
He is doing work
When he holds the barbell
there until the judges say he
can put it down,
He is NOT doing work
Work
What is work to you?
To a scientist, work is done
when motion is involved.
WORK
is the transfer of energy through motion
in order for work to take place, a force
must be exerted through a distance
Ex: Lifting Boxes
work, like energy is measured in joules (J)
is force multiplied by distance
– Work=Force x Distance or W=Fxd
The amount of work
depends on two things:
1.The amount of force exerted
2.The distance over which the
force is applied
CALCULATING WORK
W=Fxd
Ex 1: A chair weighing 3.5 N is lifted 3m. How
much work was done?
10.5J
Ex 2: A force of 25N is used to push a box
along the floor a distance of 4 meters. How
much work was done?
100J
Ex 3: It took 75J to push a desk 5m across the
floor. With what force was the desk
pushed?
15N
Ex 4: A force of 300N was necessary to
lift a file cabinet. A total of 150J of
work was done. How far was the file
cabinet lifted?
.5m
Ex 5: A carpenter lifts a 35N beam 1.4m.
How much work is done on the beam?
49J
Ex 6: A student lifts a 10N stack of
books 2.1 meters. How much work is
done on the books?
21J
Calculating
Work
Independent
Practice
Power
is the amount of work done in a certain amount of
time; rate at which work is done
Power=work
time (sec)
is measured in Watts (W)
CALCULATING POWER
Power=work/time
Ex 1: A set of pulleys is used to lift a crate
weighing 1,500N. The crate is lifted 3
meters in 50 seconds. How much power is
used?
90W
Ex 2: How much power is used is a force of
45N is used to push a desk a distance of 15
meters in 5 seconds.
135W
Calculating
Power
Independent
Practice