PHYS 2001 Lecture Notes - Lecture 13: Joule, Tennis Ball
Pterodactyls watch as an asteroid plunges thru Earth’s atmosphere. This is
an artist’s conception of a catastrophic event thought to have led to the
extinction of the dinosaurs. During an impact, an asteroid only 1 km across
releases its
energy
of motion as heat and light delivering the explosive
releases
its
energy
of
motion
as
heat
and
light
,
delivering
the
explosive
equivalent of 100 million atomic bombs.
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find more resources at oneclass.com
Chapter 6 – Work and Energy
6.1 Work done b
y
a constant force
y
Energy. What is it??? You all probably have an idea of what energy is.
It comes in many forms: mechanical, chemical, heat, light, nuclear, etc.
And energy comes in two types:
Kinetic Energy – Energy of motion
Potential Energy
Energy due to position
Potential
Energy
–
Energy
due
to
position
Energy is governed by certain laws which we will learn in this chapter.
And we will find that solving certain problems with an energy approach is
And
we
will
find
that
solving
certain
problems
with
an
energy
approach
is
often much easier than using Newton’s Laws.
But both of these very different approaches are linked through a common
concept and that is the concept of
Work
concept
,
and
that
is
the
concept
of
Work
.
We all have our own ideas about what work means to us, but in physics,
work is very explicitly defined.
I
t
i
s
de
fin
ed
in
te
rm
s
o
f F
o
r
ce
a
n
d
Di
sp
l
ace
m
e
n
t
.
tsde ed te so
oce
ad
sp ace e t
Work done on an object by a constant force:dFd
⋅
=
W
(*Note: Do not confuse work with weight!)
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dFd⋅=WIn words, Work is equal to Force times distance.
Units?
[]
ent)(displacemForce)( ×
[
]
mN
⋅
≡
[
]
J≡(Joules)
N tht k ht ki liitl dfi E
N
ow
th
a
t
we
k
now w
h
a
t
wor
k
i
s, we can more exp
li
c
itl
y
d
e
fi
ne
E
nergy:
En
e
r
gy
i
s
t
h
e
ab
ili
ty
to
do
w
o
rk.
In the equation for work,
F
d
is not necessarily the total force on the object, but it is
e gy s t e ab ty to do o
In
the
equation
for
work,
F
d
is
not
necessarily
the
total
force
on
the
object,
but
it
is
the net force (or component of the force) along the direction of motion, i.e. either
in the same direction as the displacement, d, or in the opposite direction of the
displacement, d.
Work is a scalar, not a vector, but it can be either positive or negative.
Work is positive if the force and displacement are in the same direction.
Work is negative if the force and displacement are in opposite directions.
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Document Summary
Pterodactyls watch as an asteroid plunges thru earth"s atmosphere. This is an artist"s conception of a catastrophic event thought to have led to the extinction of the dinosaurs. During an impact, an asteroid only 1 km across releases its energy of motion as heat and light delivering the explosive releases its energy of motion as heat and light, delivering the explosive equivalent of 100 million atomic bombs. 6. 1 work done by a constant force y. You all probably have an idea of what energy is. It comes in many forms: mechanical, chemical, heat, light, nuclear, etc. Energy is governed by certain laws which we will learn in this chapter. And we will find that solving certain problems with an energy approach is. And we will find that solving certain problems with an energy approach is often much easier than using newton"s laws.
