Download PPTintro - Dr. Robert MacKay

Work and Energy
Dr. Robert MacKay
Clark College
Introduction
What is Energy?
 What are some of the different forms of
energy?

Energy = $$$
Overview
Work (W)
Kinetic Energy (KE)
Potential Energy (PE)
 All Are measured in Units of Joules (J)
 1.0 Joule = 1.0 N m

W
KE
PE
Overview

Work Kinetic Energy
Potential Energy
Heat Loss
W
Heat Loss
KE
PE
Heat Loss
Work and Energy
Work = Force x distance
W=Fd
 Actually
 Work = Force x Distance parallel to force

d=4.0 m
F= 6.0 N
W= F d
= 6.0 N (4.0m)
= 24.0 J
Work and Energy

Work = Force x Distance parallel to force
d= 8.0 m
F= 10.0 N
W=?
Work and Energy

Work = Force x Distance parallel to force
d= 8.0 m
F= 10.0 N
W = 80 J
Work and Energy

Work = Force x Distance parallel to force
d= 8.0 m
F= - 6.0 N
W= F d
= -6.0 N (8.0m)
=-48 J
Work and Energy

Work = Force x Distance parallel to force
d= 6.0 m
F= - 5.0 N
W= F d
=?J
Work and Energy

Work = Force x Distance parallel to force
d= 6.0 m
F= - 5.0 N
W= F d
= -30 J
Work and Energy

Work = Force x Distance parallel to force
F= + 6.0 N
d= 8.0 m
W= 0
(since F and d are perpendicular
Kinetic Energy, KE
 KE
=1/2 m v2
m=2.0 kg and v= 5 m/s
KE= ?
Kinetic Energy
 KE
=1/2 m v2
m=2.0 kg and v= 5 m/s
KE= 25 J
Work Energy Theorm
 KE
=1/2 m v2

F=ma
Work Energy Theorm
K
=1/2 m v2

F=ma
Fd=m a d

Work Energy Theorm
 KE



=1/2 m v2
F=ma
F d =m a d
F d = m (v/t) [(v/2)t]
Work Energy Theorm
K
E=1/2 m v2

F=ma
Fd=mad
F d = m (v/t) [(v/2)t]
W = 1/2 m v2



Work Energy Theorm
 KE





=1/2 m v2
F=ma
Fd=mad
F d = m (v/t) [(v/2)t]
W = 1/2 m v2
W = ∆ KE
Potential Energy, PE
•
•
•
•
•
Gravitational Potential Energy
Springs
Chemical
Pressure
Mass (Nuclear)
• Measured in Joules
Potential Energy

Gravitational Potential Energy = weight x height
PE=(mg) h
4.0 m
m = 2.0 kg
Potential Energy
PE=(mg) h
PE=80 J
m = 2.0 kg
4.0 m
K=?
Conservation of Energy
Energy can neither be created nor destroyed only
transformed from one form to another
Total Mechanical Energy, E = PE +K
In the absence of friction or other non-conservative forces
the total mechanical energy of a system does not change
E f=Eo
Conservation of Energy
PE=100 J
K=0J
m = 1.02 kg
(mg = 10.0 N)
PE = 75 J
K = 25 J
10.0 m PE = 50 J
K = 50 J
PE= 25 J
PE = 0 J
Constant E
{E = K + PE}
Ef = Eo
K= ?
K=?
No friction
No Air resistance
W  FD//
Crib Sheet
(JOULES)
1 2
KE  mv
2
GPE  mgh
1 2
SPE  kx
F  kx
2
W
P
(J / s  Watt)
t
Wnet  KE
E  KE  PE
E f  E 0  W NC