Transcript I. Energy & Work

Ch. 5 - Energy
I. Energy and Work (p.124-131)



Energy
Work
Conservation of Energy
A. Energy
THERMAL
The ability to
cause change.
internal motion of
particles
MECHANICAL
NUCLEAR
ENERGY
motion of objects
changes in the
nucleus
ELECTRICAL
CHEMICAL
bonding of atoms
joules (J)
motion of electric
charges
A. Energy

Kinetic Energy (KE)
 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

Potential Energy (PE)
 stored energy
 depends on position or
configuration of an object
• Which boulder has greater
gravitational PE?
• What other ways can an
object store energy?
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.