1405 12 2008c Name ________________________________________
Elasticity
Materials
5 Equal Sized Rubber Bands
1 5N spring scale
Objectives
Explore elasticity and force-deformation behavior
Determine “stiffness” and its dependence of on size of object.
Introduction
The stiffness of an elastic object is found by dividing the change in its length into
the force that caused the length change. The units we will use will be N/cm. If N
is large and cm are small then the object will have a high stiffness. If N is small
but causes a large cm change in length, then the object will have a small
stiffness.
Procedure
Link the rubber bands as noted in each table.
Pull until about 0.2N registers. Place the 0cm at that point. Pull until 2.5N is
registered. Record the change in length and calculate the stiffness.
Table 1:
2.5N Stretching Force
#bands
change in length (cm)
side-by-side
stiffness (N/cm)
(Force/change in length)
1
2
3
4
5
Table 2:
2.5N Stretching Force
#bands
link-to-link
1
2
3
4
5
change in length (cm)
stiffness (N/cm)
(Force/change in length)
1405 12 2008c Name ________________________________________
Summing Up
1. What arrangement of rubber bands is about 3x stiffer than one single rubber
band? Explain referring to your data.
2. What arrangement of rubber bands is about 1/3 as stiff as one single rubber
band? Explain referring to your data.
3. The increase in side-by-side stiffness of rubber bands in relation to the
number used is
__ above proportional
__ proportional
__ less than proportional
4. The decrease in link-to-link stiffness of rubber bands in relation to the number
used is
__ above inverse proportional
__ inverse proportional
__ less than inverse proportional