Transcript I. Energy & Work

Ch. 5 - Energy
I. Energy & Work (pp. 256-332)
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Energy
Work
Conservation of Energy
Thermal Energy
Make a table in your notes
Type of Energy
Description
Examples
A. Energy Types
THERMAL
HEAT
ELECTROMAGNETIC
internal energy of transfer of energy b/c of a El’c and mag’c energy in the
difference in temp.
form of waves
particles
NUCLEAR
ENERGY
MECHANICAL
Energy released b/c of
changes in the nucleus
(fission or fusion)
The ability to
cause change.
Energy of moment/
potential movement
CHEMICAL
Measured
in joules (J)
PE held in bonds
between atoms
SOUND
Mechanical wave through medium
RADIANT/LIGHT
“visible;” emitted by
moving charged particles
ELECTRICAL
motion of electric charges
A. Energy

Potential Energy (PE = mgh)
 stored energy
 depends on position or
configuration of an object
• Which boulder has greater
gravitational PE?
• What other ways can an
object store energy?
A. Energy

Kinetic Energy (KE = ½ mv2)
 energy in the form of motion
 depends on mass and velocity
• Which has the most KE?
80 km/h truck
• Which has the least KE?
50 km/h motorcycle
80 km/h
50 km/h
80 km/h
A. Energy Problems

Calculate the KE of a 40 kg girl
running on a track at 15 m/s.

Calculate the gravitational PE of a
50 kg boy at the top of the stadium
(12.5 m).
B. Work

Work
 transfer of energy through motion
 force exerted through a distance
W = Fd
W:
F:
d:
work (J)
force (N)
distance (m)
1 J = 1 N·m
Distance must be in direction of force!
B. Work

Brett’s backpack weighs 30 N. How much
work is done on the backpack when he lifts
it 1.5 m from the floor to his back?
GIVEN:
F = 30 N
d = 1.5 m
W=?
WORK:
W = F·d
W = (30 N)(1.5 m)
W = 45 J
W
F d
B. Work

A dancer lifts a 40 kg ballerina 1.4 m in the air
and walks forward 2.2 m. How much work is
done on the ballerina during and after the lift?
GIVEN:
m = 40 kg
d = 1.4 m - during
d = 2.2 m - after
W=?
W
F d
WORK:
W = F·d
F = m·a
F =(40kg)(9.8m/s2)=392 N
W = (392 N)(1.4 m)
W = 549 J during lift
No work after lift. “d” is not
in the direction of the force.
C. Conservation of Energy

Law of Conservation of Energy
 Energy may change forms, but it
cannot be created or destroyed
under ordinary conditions.

EX:
 PE  KE
 mechanical  thermal
 chemical  thermal
C. Conservation of Energy
PE  KE
View pendulum animation.
View roller coaster animation.
C. Conservation of Energy
Mechanical  Thermal
View rolling ball animations.
View skier animation.