LAB
I: ELASTICITY
Problem:
What is the relationship between the force applied to a spring
and the stretch of the spring?
NOTE: DO
NOT BEGIN YOUR EXPERIMENT UNTIL EACH PERSON IN THE GROUP HAS READ
THE BACKGROUND AND ANSWERED THE BACKGROUND QUESTIONS.
Background
and Inquiry: Today you will study some properties of elastic
bodies. An elastic body has the ability to regain its original
form after it is stretched. A spring is one example of an elastic
body. Observe the properties of the spring by pulling slowly on
the spring and observe the tension in the spring. DO NOT PULL
THE SPRING TO FULL EXTENSION!! If an elastic body is stretched
beyond a point called the elastic limit, it will no longer retain
its original properties. By feeling the tension on the spring
discuss with your group how changes in force may the affect the
amount of stretch observed.
Many things
in nature have elastic properties. A rubber band is one example.
A spring is another. Can you think of others? Discuss with your
group several other examples of elastic bodies.
Take the rubber
band and stretch it being careful not to extend it too far. Have
each person in the group observe the properties of the two elastic
bodies (spring and rubber band). Discuss any differences in their
properties.
Today you
will study the elastic properties of a spring and two different
types of rubber band. Your problem today is to determine the relationship
between the force needed to stretch an elastic body and the length
it stretches. For your hypothesis try to predict the type of behavior
you expect the spring and rubber band to follow as you change
the amount of force (mass weights) applied to the spring. For
example, would you expect if you double the weight the spring
will stretch twice as much? Or three times? What type of relationship
do you predict will occur?
Background
Questions:
1) What is
an elastic body?
2) Give 4 examples of elastic bodies.
3) Do you think the elastic properties of all elastic bodies are
the same? Why?
Hypothesis:
State your hypothesis to the problem. Justify your reason.
.
Materials:
ruler, spring, set of weights, ring stand, two different types
of rubber band
Procedure:
1)
Copy Table I, Table II, and Table III into your lab notebook.
2) Set
up the equipment as shown in in class.
3) Starting
with the smallest mass, measure the amount the spring is stretched
(difference in length between spring without mass and with mass).
See your class notes on how to measure this difference. Use additional
masses as shown in Table I below. For each mass measure the the
stretch. DO NOT EXCEED 500 GRAMS FOR THE SPRING.
3)
Repeat step 3 using the rubber bands, instead of the spring.
Results:
Note: To
simplify this lab we will only use mass in your tables and graph.
See your class notes for clarification.
TABLE I
SPRING
Mass (g.) 
Stretch (cm.) 
100 

200 

300 

400 

500 

TABLE II
RUBBER
BAND 1 (THIN)
Mass (g.) 
Stretch (cm.) 
100 

200 

300 

400 

500 

600 

700 

800 

TABLE III
RUBBER
BAND 2 (THICK)
Mass (g.) 
Stretch (cm.) 
100 

200 

300 

400 

500 

600 

700 

800 

Graph the
data from Table I and Table II drawing two graphs, both on the
same set of axis. Plot stretch (cm.) on the yaxis and mass
(grams) on the xaxis. Make sure to label each axis, and each
plot. Measure and record the slope of each plot Give the completed
set of graphs a title.
Discussion:
Be sure to
include the following:
1) What type of mathematical relationship is demonstrated in Graph
I? Why?
2) Does graph II and III show more than one relationship? For
example, does the graph start off linear then change? If so explain
why.
3) What
are the variables in this experiment? Which is the dependent
variable, which is the independent variable?
4) How are the variables changing with relationship to each other?
5) What are some factors that are held constant in this
experiment?
6) Can you predict what the stretch would be in Table I if 350
grams were attached to the spring? Why?
7) Can you predict what the stretch would be in Table I if 800
grams were attached? Why? or Why not?
Applications:
1) How can
your graph be used to find the force of an unknown object?
2) Design an experiment to predict if a spring has been overstretched
and is deformed.
3) Research Hooke's Law. How does it relate to this lab?
