International Baccalaureate Physics
4/PSOW
To Measure the Stiffness of Steel by the
Oscillations of a Hacksaw Blade
In this IB Lab you will be assessed on the following IB criteria:Data Collection, Data Processing and Evaluation
Aim:
This is to show that a concept difficult to measure can be easily calculated indirectly from a suitable
equation. Also this is further practice in plotting an appropriate graph and using the gradient to find a
constant - in this case the constant is the stiffness (E) of the steel. Also you will see how to use your
graph to obtain a  estimate of accuracy.
Apparatus:
Clamp, hacksaw blade, stop watch, 2 magnets, ruler, micrometer, digital scales, blocks of wood.
X
Diagram:
Magnets M
Hacksaw blade
Clamp
Method:
Clamp the hacksaw blade between the 2 blocks of wood with the blade vertical. Attach the 2 magnets
to the end of the blade, about 0.15 m from the blocks (distance x). Pull the magnets to one side and
release them so that the blade vibrates. Time the period T. Repeat this for various lengths of x up to
0.3 m. Also measure the mass of the magnets (M), the thickness of the hacksaw blade (d), and the
breadth (b).
Data Collection:
Period T, mass M and stiffness E are related by the equation:
16 2 M  3
T 
x
3
 bd E 
2

Draw a suitable table to include all of the variables together with their actual uncertainties and
percentage uncertainties due to the apparatus used.
Data Processing and Presentation:
 Plot a suitable graph that will allow you to find the stiffness E.
 What is the accuracy of your result?
 To estimate this, find the best-fit line on the graph and the worst fit line.
 Calculate a value for E from each gradient and so find a  value for your result for E.
Conclusion and Evaluation:
 What does the term “stiffness” mean?
 What is the value of the stiffness (E) for steel?
 How does this value compare with the one that you have obtained.
 Suggest reasons for any differences.
 Suggest areas where the procedures used in this practical may have been the cause of some of
these errors.
 Suggest modifications to the practical to minimise any errors and shortcomings.
Mike Dickinson
533576177