Hooke’s Law Experiment
Introduction
Students will formulate a hypothesis based on the observation of stretching a rubber
band. Then they will design and perform a simple experiment to study the extension
of a spring and collect, interpret and analyse data. Based on the experimental results,
students can verify whether the hypothesis is accepted or rejected. At the end of the
activity, students will share their experimental results and conclusions, designs, and
the final products with teacher and classmates. Then teacher and classmates provide
appropriate feedback. Students will learn to work collaboratively and the teacher
stimulates students to think and solve scientific and technological problems.
Learning objectives
1.Identify the major steps in carrying out a scientific investigation.
2.Acquire the skills in performing a scientific investigation.
3.Collect, interpret, analyse and evaluate scientific information.
Work allocation
Students will work together in groups of 5 to 6 to carry out this scientific
investigation.
Activities
Making Observation
Stretch a rubber band with both hands and record your observations.
Formulating Hypothesis
Based on your observations, formulate a hypothesis.
Testing Hypothesis
You are provided with the following materials:
 Spiral spring with pointer.
 Stand with an adjustable mirrored scale (15 cm).
 Slotted weights (10 g, 20 g, 50 g).
Design an experiment to test the hypothesis.
(Hints on designing an experiment to test the hypothesis:
 You need to perform several measurements to collect a set of data correlating the
weights and the extension of spring. Then a graph of weight vs. extension of spring
is plotted in order to verify the formulated hypothesis.
Fx
A plot of weight, F vs. extension, x, should yield a straight line passing through the
origin.)
Data Analysis
1.
Tabulate the data as shown in the following table.
Weight, F (g)
2.
Length of spring (cm)
Extension of spring, x (cm)
Plot a graph of weight (in g) vs. extension of spring (in centimetres).
Weight, F (g)
A Plot of Weight vs. Extension of Spring
Extension of Spring, x (cm)
Drawing Conclusion
Would you accept or reject the hypothesis?
Why?
(Hints on drawing conclusion:
 When the plotted graph is a straight line passing through the origin, there is a direct
proportionality between the weight load, F, and the extension of a spring, x, i.e. F 
x. Hence, the hypothesis can be accepted.
 If the plotted graph is not a straight line, the hypothesis should be rejected.)
Principle of Experiment  Hooke’s Law
One of the properties of elasticity is that it takes about twice as much force to stretch a
spring twice as far. The linear dependence of displacement upon stretching force is
called Hooke’s Law. Hooke’s Law states that the force exerted by a spring (an elastic
material) is proportional to the distance the spring stretched or compressed from its
relaxed position.
Fx
where
F is the applied force (e.g. weight of hanging object from a
vertical spring)
x is the extension (or compression) of the spring
unstretched
spring
x
F x
F
It takes
twice as
much
force to
stretch a
spring
twice as
far.
2x
2F
If too large a force is exerted on a spring, the spring may be ruined. When this occurs,
the extension x increases to very large values, not according to Hooke’s Law. When
the force is removed, the spring does not return to its original length. We say that the
elastic limit is exceeded. So Hooke’s Law applies only if the elastic limit is not
exceeded.
Suggested Procedure for Testing Hypothesis
To verify the hypothesis derived from the observation of stretching a rubber band,
i.e., applied force (weight)  extension of elastic material.
Materials
 Spiral spring with pointer.
 Stand with an adjustable mirrored scale (15 cm).
 Slotted weights (10 g, 20 g, 50 g).
Procedure
1.Set up the apparatus as shown in Figure A1.
Figure A1.
2.Record the starting position of the spring at its relaxed state as indicated by the
marker attached to the spring.
3.Add 20 g slotted weight to extend spring to a measurable displacement (x).
Record the weight and the length of spring to calculate the extension x.
4.Repeat Step 3 for four more trials using different weight loads (e.g. 40, 60, 80, 100
g).