PHYS 1405 Elasticity
Name ________________
Materials
(5) Equal Sized Rubber Bands
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)
(2.5/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)
(2.5/change in length)
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 change in side-by-side stiffness of rubber bands is roughly
__ inverse proportional to the number used
__ inverse-square proportional to the number used
__ proportional to the number used
4. The decrease in link-to-link stiffness of rubber bands in relation to the number used is
__ above inverse proportional
__ close to inverse proportional
__ less than inverse proportional