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Exploring Elasticity Lab
Activity 3B
Using equipment, a set of weights, and elastic tubes, students will
be able to:
Activity Overview
Activity Objectives:
Activity Description:
Students will investigate Hooke’s law by studying the elastic properties
of various sized tubing, especially the relationship between a force that
stretches an elastic body and the length the elastic body stretches.
Students will apply a known force to several elastic tubes and measure
resulting changes in the circumference and length. Once students
acquire a basic understanding of elasticity, they will relate this concept
to the cardiovascular system.
Activity Background:
A material that can resist stretching and return to its original size and
shape when a force is applied and then removed is elastic. An object is
more elastic if it returns more exactly to its original size and shape.
For example, think of a ponytail holder and a guitar string.
The guitar string resists stretching and returns to its original length even after continual usage. A ponytail holder
will lose its shape much faster under continual usage
and is thus less elastic than the guitar string. Using a
spring as an example of an elastic object, a weight hanging
on the end of the spring as shown in Figure 1, Spring Elasticity, applies
a stress to the spring. When the weight pulls on the spring, the spring
will pull back in an attempt to resist stretching, but will lengthen to
some degree under the stress of the weight. The stretch of an elastic
object due to an applied force is called strain. (See Figure 1, Spring
Elasticity). The same principle applies to other elastic bodies such as
the tubes used in this activity.
2005 PROTOTYPE
Positively Aging®/M.O.R.E.
2004©The University of Texas Health Science Center at San Antonio
INFLAMM-O-WARS
u investigate the properties of elastic bodies
u measure how changes in force may affect the amount of
extension (stretch) in an elastic body
u distinguish between extension (strain) and force of weight (stress)
u provide a definition of Hooke’s law
u apply the principle of elasticity to human blood vessels
u graph their data to find that strain is proportional to stress
LESSON 3
ACTIVITY 3B
1
x
It takes
twice as
much force
to stretch a
tube twice
as far.
2x
Figure 1 Spring Elasticity
Activity Overview
Unstretched
tube
How does elasticity relate to the human body? The cardiovascular
system consists of the heart and blood vessels (arteries, veins, and
capillaries) and elasticity is an important property that allows our blood
vessels to function properly. Arteries receive blood that is pumped away
from the heart under pressure – this stretches arterial walls. Elastic fibers
in arterial walls ensure that the vessel returns to its original shape.
Arterial Elasticity keeps pressure on the blood inside, smoothing out the
flow of the blood even when the heart relaxes; this pressure keeps the
blood moving. Elastic recoil keeps blood moving though the capillaries –
without it, the heart would have to work much harder. The elastic
properties of arteries change with age and with disease. Arteriosclerosis
is a disease in which arteries lose elasticity as their walls became stiff
and inflexible; often as a result of high blood pressure exerting excess
force against arterial walls. Atherosclerosis is a disease that begins with
inflammation and causes arteries to become blocked. Atherosclerosis
used to be considered an old person’s disease; however, it begins in
childhood and progresses through young adulthood to cause coronary
heart disease (CHD). Fatty streaks and lesions have been found in youth
as early as 15 years of age.
It is important to understand the elastic behavior of arteries in terms
of force and motion. In an elastic tube, such as an artery, the blood
inside exerts a force by pushing against the walls to create a stress.
The greater the force on artery walls, the less elastic and more stiff they
2005 PROTOTYPE
Positively Aging®/M.O.R.E.
2004©The University of Texas Health Science Center at San Antonio
INFLAMM-O-WARS
In an elastic material, strain is proportional to stress. This means that
the larger the weight (stress) hanging on a spring (or other elastic
material), the more it will stretch (strain). This principle of elasticity is
called Hooke’s Law. The point at which elastic materials do not obey
Hooke’s Law is known as the elastic limit. When the elastic limit of a
material is not exceeded, the material will go back to its original length
when the weight (stress) is removed. However, if too much weight is
added, the material will stretch without going back to its original length
when the weight is removed. A very large weight hanging on an elastic
object, will cause the object will get longer and longer until it breaks.
LESSON 3
ACTIVITY 3B
2
Activity Materials:
•
•
•
•
*
Ring stand
Clamp
Spring scale (compatible with range of weights)
Metric measuring tape
4 large binder clips*
4 medium binder clips*
(1) 10 cm and (1) 15 cm stretchy rubber tube with the same inside
and outside circumference, labeled A and B**
(2) 15 cm stretchy rubber tubes with different sized inside and
outside circumferences, labeled C and D**
tubes available at Analytical Scientific or other science
supply source
Set of weights (100 gram increments)
(available through science supply stores)
Safety goggles
1 set of task cards per group (these can be laminated and reused
from class to class)
By pinching sides together, the silver clasps are
removed from binder clips. Insert one clasp into
each end of the tube as shown in Figure 2. Pinch
the tip of the binder clip and push into the tube as
far as possible, then use the tip of a small knife to
make a very small hole that allows the end of the
clip to protrude through the tubing. Teacher
should prepare the tubes prior to doing activity.
Activity Management Suggestions:
Modifications:
Clasp from
binder clip
Tube
Clasp from
binder clip
Figure 2
This activity may be arranged as a center or as part of several lab stations around the classroom. The teacher can write up easy to follow
instructional cards, which guide the student and limit teacher direction.
Extensions:
Inquiry activity to determine other materials that obey Hooke’s Law.
2005 PROTOTYPE
Positively Aging®/M.O.R.E.
2004©The University of Texas Health Science Center at San Antonio
INFLAMM-O-WARS
•
•
•
•
•
•
•
(per group)
Activity Overview
become. If an artery wall goes beyond its elastic limit, a rupture may
cause bleeding which can result in irreparable damage or death.
Maintaining higher elasticity in the arteries is necessary for managing
vascular health. Blood vessel elasticity can be maintained by eating a
low-fat, healthy diet, exercising, maintaining a healthy body weight,
and keeping blood pressure within a healthy range. Teaching students
about the elastic properties of arteries will encourage them to make
positive changes that can affect their young lives.
LESSON 3
ACTIVITY 3B
3
Activity References Used:
Ovadia-Blechman, Z., Einav, S., Zaretsky, U., Castel, D., Eldar, M.
(2003).Characterization of arterial stenosis and elasticity by analysis of
high-frequency pressure wave components. Computers in Biology and
Medicine 33, 375-393.
Darvill, A. (2005). Springs: Hooke’s law and elastic limits. Retrieved July20,
2005 from GCSE Physics Website:
http://www.darvill.clara.net/enforcemot/springs.htm#top
Hoult, D. (2004). Mechanics. Retrieved July 19, 2005 from Ecole Active
Bilingue Jeannine Manuel in Paris, The Open Door Team Website :
http://www.saburchill.com/physics/practicals/004.html
Purchon, N.D. (1997-2000). Hooke’s Law. Retrieved from Gondor Design
Science Website: http://www.purchon.com/physics/hookeslaw.htm
White, H., Trenwith, F., Karalius, L., Sherlock, J., Berry, P. (1999).
Hooke’s Law. Retrieved June 9, 2005 from University of Liverpool,
MATTER Project Website:
http://schools.matter.org.uk/Content/HookesLaw/index.html
Activity Overview
McMahan, C.A., Gidding, S.S., Fayad, Z.A., Zieske, A.W., Malcom,
G.T.,Tracy, R.E., et al. (2005). Risk scores predict atherosclerotic lesions in
young people. Arch Intern Med., 165, 883-890. Retrieved June 6, 2005,
from www.archinternmed.com
Elasticity. (n.d.) Retrieved July 19, 2005 from Columbia Encyclopedia,
sixth edition Website: http://www.encyclopedia.com/html/e1/elastici.asp
2005 PROTOTYPE
Positively Aging®/M.O.R.E.
2004©The University of Texas Health Science Center at San Antonio
INFLAMM-O-WARS
Special thanks to Mary Poarch and her students at Alamo Heights ISD
for field testing this activity.
LESSON 3
ACTIVITY 3B
4