Download thermal energy

Section 1: The Nature of Energy
• Energy is the ability to cause change.
• There are many different forms of energy:
– chemical
– thermal
– kinetic
– potential
– electrical
Potential and Kinetic Energy
Kinetic Energy
• energy in the form of motion
• KE = ½ mass x velocity2
KE = ½ m x v2
• SI unit—Joule (J)
Potential Energy
• stored energy due to position
• types of potential energy
– elastic: energy stored by something that can
stretch or compress (ex. rubber band, spring)
– chemical: energy stored in chemical bonds
(ex. gasoline, food)
– gravitational: energy stored by objects that
are above Earth’s surface
(ex. apple or leaf in tree)
Gravitational Potential Energy
(GPE)
• GPE = mass x 9.8 m/s2 x height
• SI unit—Joule (J)
• Bjorn is holding a tennis ball outside a 2nd story
window (3.5 m from the ground) and Billie Jean
is holding one outside a 3rd story window (6.25
m from the ground). How much more GPE does
Billie Jean’s tennis ball have? (Each tennis ball
has a mass of 0.06 kg).
Section 2: Conservation of Energy
• Energy is most noticeable as it transforms
from one form to another.
• mechanical energy = total energy (kinetic
+ potential)
Bonus: How do your
kinetic and potential
energy relative to an
elevator change as
you go up?
Energy Conversion
Law of Conservation of Energy
• Energy cannot be created or destroyed.
• The total amount of energy in the universe
remains constant.
Work
(Chapter 5-1)
• Work is the transfer of energy that occurs
when a force makes an object move.
• Two conditions must be met for work to be
done on an object:
– the object has to move
– the movement must be in the direction of the
force
Work and Energy
• When work is done, a transfer of energy
always occurs.
Calculating Work
• Work = force x distance
W=Fxd
• SI unit: Joules (J)
• One joule is about the amount of work
required to lift a baseball a vertical
distance of 0.7m.
Example Problems
• You move a 75 kg refrigerator 35 m. This
requires a force of 90 N. How much work
was done while moving the refrigerator?
– 3150 J
• When you and a friend move a 45 kg
couch to another room, you exert a force
of 75 N over 5 m. How much work did you
do?
– 375 J
Bonus
• Suppose you used a force of 50 N to shoot
an arrow, and the arrow flew 25 meters.
As you shot the arrow, the bow string
moved the arrow 1 m. Did you do 1250 J
of work or 50 J of work? Explain.
– You did 50 J of work, because
after the arrow left the bow, it
flying loose in the air and
not experiencing any
force from you.
was
was
Power
• Power is the amount of work done in a
certain amount of time (the rate at which
work is done).
• Power = work / time
P=W/t
• SI unit: watts
• Example: How much power is required to
push a car for 10 s if the amount of work
done during that time is 5,500 J?
– 550 W
Temperature and Heat
(Chapter 6)
• All matter is made up of tiny particles in
constant motion, meaning that they have
kinetic energy.
• temperature: average kinetic energy of the
particles
• thermal energy: total energy of all the
molecules in an object
• A larger mass has more thermal energy
than a smaller mass at the same
temperature, because there are more
particles in the larger mass.
• When the temperature of an object
increases, the average kinetic energy of
the molecules increase, so the thermal
energy increases.
Heat
• heat: energy that is transferred from an
object at a high temperature to one at a
lower temperature
• Heat and work are similar. Both are
energy being transferred. Both are
measured in joules.
• calorimeter: instrument used to measure
changes in thermal energy
Transferring Thermal Energy
Conduction
• conduction: transfer of energy through
matter by the direct contact of particles
• Conduction occurs because of the
collisions between particles.
• insulators: material that doesn’t allow heat
to flow through it easily
Convection
• fluid: anything that flows (liquids, gases)
• convection: transfer of energy in a fluid by
the movement of the heated particles
• Convection currents are rising-and-sinking
actions that transfer heat from warmer to
cooler parts of a fluid.
Radiation
• radiation: transfer of energy by electromagnetic
waves
• Electromagnetic waves can travel through space
even when no matter is present.
• When radiation strikes a material, some of the
energy is absorbed, some is reflected and some
may be transmitted through the material.