PHYSICS 534
R
E
W
S
N
EXERCISE-18
A
S
Elasticity
Max von Laue received
the Nobel prize for physics
in 1914 for his work with
crystal diffraction in X-rays.
von LAUE
Two equal but opposite applied forces acting in parallel produce what is called a "stress".
A stress can be considered as a force "inside" a solid material produced by two parallel forces acting on the material.
If the stress is within the “elastic limit” of the material, the material will return to its original shape when the stress is
removed. If the stress causes the material to deform beyond its elastic limit, the material will be permanently deformed
when the stress is removed.
Strain refers to the deformation a material undergoes due to a stress acting on it. The strain can be temporary when the
stress acts within the elastic limit, or permanent when the stress acts beyond the elastic limit. Strain is simply the shape
of the deformation.
S
T
R
E
S
S
W
ith
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le
as
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it
(R
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d
)
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ion
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tr
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 Note: A wire (or string or rope) is under "tension" when pulled
and has two equal but opposite forces acting on it. The
S
h
a
r
in
g
tension
ise
equal
to the applied force pulling the wire
(even though the resultant force is zero). In the illustration
on the right, a rope is attached to a wall and is pulled with
an applied force FA equal to 100 N.
1.
B
e
yon
de
las
ticlim
it
(D
e
for
m
e
d
)
S
T
R
A
I
N
W
a
l
l
W
a
l
l
f
o
r
c
e
W
a
r
p
e
d
F
=
1
0
0
N
W
A
p
p
l
i
e
d
f
o
r
c
R
o
p
e
Define elasticity.
______________________________________________________________________
The ability of a material to be stretched.
2.
Explain the difference between a perfectly elastic and a perfectly inelastic material.
______________________________________________________________________
In a perfectly elastic material, there is no energy loss.
In a perfectly inelastic material, there is total energy loss.
______________________________________________________________________
PHYSICS 534  STATICS  AnsPhysics Ex-18.DOC
© 1999 S. Lancione
Page 1 /2
F
=
1
0
0
N
A
3.
Define stress.
Two equal but opposite forces acting in parallel.
______________________________________________________________________
4.
Define strain.
______________________________________________________________________
The deformation that an object undergoes due to a stress.
5.
A 20 kg object is suspended from a ceiling by a wire.
What is the tension in the wire?
Ceiling
___________________________________________
Since the object is at rest, FR  0.
Thus,  FUP   FDOWN
___________________________________________
 FUP  (20 kg)(10 m / s 2 )  200 N
6.
Wire
20 kg
List the five types of stress, draw the forces corresponding to the stresses acting on an
object (under FORCES), and state the strain associated with each stress:
Write the
Draw the
Write the
STRESS
FORCES
STRAIN
a)
Tension
Stretched
b)
Compression
Shortened
c)
Bending
Bent
d)
Twisting
Twisted
e)
Shearing
Warped

PHYSICS 534  STATICS  AnsPhysics Ex-18.DOC  Elasticity
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