Hooke's Law.

Experiment 7
HOOKE’S LAW
EQUIPMENT
Cricket Graph program
1 right angle clamp
1 rubber band, long
1 pan mass
1 set slotted masses
INTRODUCTION
1 long metal rod
1 table clamp
1 short metal rod
1 spring
1 meter stick
1 c-clamp
The purpose of this experiment is to investigate the
relationship between the change in length of a spring
and the force applied to it.
An applied force may deform an object in several ways.
The object may be compressed, stretched, bent or
twisted. Hooke’s law describes the relationship
between the applied force and the amount of
deformation of the object. The stretching of a spring is a
good example of Hooke’s law. A mass hanging on a
spring causes the spring to stretch. More mass will
cause the spring to stretch still more. Hooke’s law
indicates that the elongation of the spring, x, is directly
proportional to the force applied by the hanging mass.
We can write this as an equality given by
4. Place a 150g mass on the pan and read and record
the new position of the pan. Also record the mass
and calculate the force it causes on the spring.
(Use g = 10 m/s 2 ; then the force of the spring
(weight) is m * g or m * 10 m/s 2 .)
5. Subtract the value of the position of the pan with no
load from the position found in Step 3. The
difference is the elongation of the spring. Record
this elongation.
6. Place additional masses in 50-gram increments on
the pan and record the new positions. Calculate
and record the force caused by the total mass on
the pan. Also calculate and record the elongation
of the spring.
F = kx
where k is a constant called the “spring constant” whose
value depends on the type of spring used.
In this experiment you will study Hooke’s law by
observing the change in length of a spring when masses
are suspended from it. Care must be taken to insure
that too great a force is not applied to the spring. When
a spring is stretched beyond its elastic limit, it will not
return to its original length when the force is removed. It
will be permanently deformed.
PROCEDURE
A. Spring
1. Suspend a spring and a weight pan from the short
rod as shown in the illustration.
2. Place a meter stick along the long metal rod so that
the end marked 0 cm is toward the ceiling. Use a
to hold the meter stick in place as shown.
3. Read the position of the bottom of the weight pan
by looking at the markings on the meter stick. This
is the reading with no load on the pan. Record this
reading on the data sheet.
7. Use your data and the CRICKET GRAPH to
construct a graph of force vs. elongation. Select
Curve Fit/Simple from the main menu. The
equation for a line is y = mx + b where m is the
slope.
B. Rubber Band
8. Repeat Steps 1 - 7 replacing the spring with a
rubber band and using mass increments of 50
grams.
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Experiment 7
DATA SHEET
Name: __________________________
Section: ________________________
Elastic Spring
Reading with no load __________ (cm)
Mass
(g)
Mass on spring
(kg)
Force on
spring
(N)
Reading with
load
(cm)
Elongation
of spring
(cm)
0 0 0 0
150
200
250
300
350
400
450
500
QUESTIONS (Answer on back of Data Sheet)
1. What is the relationship between the elongation of the spring and the weight attached to the spring? How does your
graph support or refute your answer?
2. What is the spring constant for your spring?
3. Looking at your graph for the spring, what do you predict to be the elongation of your spring when loaded with a
weight of 0.2, 2.0, and 4.0 newtons?
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Experiment 7
DATA SHEET
Rubber Band
Reading with no load __________ (cm)
Mass
(g)
Mass on spring
(kg)
Force on
spring
(N)
Reading with
load
(cm)
Elongation
of spring
(cm)
0 0 0 0
150
200
250
300
350
400
450
500
QUESTIONS (Answer on back of Data Sheet)
4. Was the graph of elongation versus force for the rubber band a straight line? In other words, is the
elongation of your rubber band proportional to the force exerted? If not, then it doesn’t follow Hooke’s
law; state a reason why.
5. Can you find a “spring constant” for the rubber band? If not, why?
6. What would finally happen to the spring if you continue to add additional weights to the spring? What
do we call this effect? And to the rubber band?
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