1. I. Energy and Work (p.124-131) Energy Work Conservation of Energy
Ch. 5 - Energy
I. Energy and Work (p )
Energy
Work
Conservation of Energy

2. A. Energy ENERGY THERMAL The ability to cause change. MECHANICAL
internal motion of particles
ENERGY
MECHANICAL
NUCLEAR
motion of objects
changes in the nucleus
ELECTRICAL
joules (J)
CHEMICAL
motion of electric charges
bonding of atoms

3. A. Energy Kinetic Energy (KE) energy in the form of motion
depends on mass and velocity
80 km/h
50 km/h
Which has the most KE?
Which has the least KE?
80 km/h truck
50 km/h motorcycle

4. 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?

5. W = Fd B. Work Work transfer of energy through motion
force exerted through a distance
W = Fd
W: work (J)
F: force (N)
d: distance (m)
1 J = 1 N·m
Distance must be in direction of force!

6. 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 F W d

7. d B. Work W F GIVEN: m = 40 kg d = 1.4 m - during d = 2.2 m - after
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 = ?
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. F W d

8. 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

9. C. Conservation of Energy
PE  KE
View pendulum animation.
View roller coaster animation.

10. C. Conservation of Energy
Mechanical  Thermal
View rolling ball animations.
View skier animation.