Ib Lab - 05 Hacksaw Blade Oscillation (dc Dpp Ce)

International Baccalaureate Physics

4/PSOW

To Measure the Stiffness of Steel by the Oscillations of a Hacksaw Blade 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. Diagram:

IB Criteria Assessed Data Collection, Data Processing, Evaluation Criteria assessed

Aspect 1

2

3

Level awarded

Pl (a) Pl (b) DC DPP CE

Hacksaw blade Magnets M

Clamp

x

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:

16π 2 M  3 T2 = x 3  bd E  •

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.

© 2006 - Mike Dickinson

8266766.doc

International Baccalaureate Physics

•

4/PSOW

Suggest modifications to the practical to minimise any errors and shortcomings.

© 2006 - Mike Dickinson

8266766.doc

International Baccalaureate Physics

4/PSOW

Internal Assessment Marking Form Crit.

Pl(a)

Pl(b)

DC

DPP

CE

Aspects Research Question: Hypothesis: Variables: c. Identifies a focused c. Relates the hypothesis or c. Selects the problem or research prediction directly to the relevant question. research question and independent p. States the problem or explains it, quantitatively and controlled research question, but it where appropriate. variable(s). is unclear or incomplete. p. States the hypothesis or p. Selects some n. Does not state the prediction but does not relevant problem or research explain it. variables. question or repeats the n. Does not state a n. Does not select general aim provided by hypothesis or prediction. any relevant the teacher. variables. Materials / Control of Variables: Collecting Data: Apparatus: c. Describes a method c. Describes a method that c. Selects appropriate that allows for the allows for the collection apparatus or control of the of sufficient relevant materials. variables. data. p. Selects some p. Describes a method p. Describes a method that appropriate that makes some allows for the collection apparatus or attempt to control the of insufficient relevant materials. variables. data. n. Does not select n. Describes a method n. Describes a method that any apparatus or that does not allow for does not allow any materials. the control of the relevant data to be variables. collected. Collecting / Recording Raw Data: Organising / Presenting Raw c. Records appropriate raw data (qualitative Data: and/or quantitative), including units and c. Presents raw data clearly, uncertainties where necessary. allowing for easy p. Records some appropriate raw data. interpretation. n. Does not record any appropriate raw data. p. Presents raw data but does not Aspect 1 includes units, uncertainties, allow for easy interpretation. significant digits n. Does not present raw data or presents it incomprehensibly. Processing Raw Data: Presenting Processed Data: c. Processes the raw c. Presents processed data appropriately, helping data correctly. interpretation and, where relevant, takes into p. Some raw data is account errors and uncertainties. processed correctly. p. Presents processed data appropriately but with some n. No processing of raw errors and/or omissions. data is carried out or n. Presents processed data inappropriately or major errors are made incomprehensibly in processing. Aspect 2 includes uncertainty bars, max / min slopes (HL), axes with labels and units, best fit line drawn Drawing Conclusions: Evaluating procedure(s) Improving the c. Gives a valid and results: investigation: conclusion, based on the c. Evaluates procedure(s) c. Identifies correct interpretation of and results including weaknesses and the results, with an limitations, states realistic explanation and, where weaknesses or errors. suggestions to appropriate, compares p. Evaluates procedure(s) improve the results with literature and results but misses investigation. values. some obvious p. Suggests only p. States a conclusion that limitations or errors. simplistic has some validity. n. The evaluation is improvements. n. Draws a conclusion that superficial or n. Suggests unrealistic

© 2006 - Mike Dickinson

Level ccc 3 ccp 2 ccn 2 cpp 2 ppp 1 cpn 1 cnn 1 ppn 1 pnn 0 nnn 0

Grade

ccc 3 ccp 2 ccn 2 cpp 2 ppp 1 cpn 1 cnn 1 ppn 1 pnn 0 nnn 0

cc 3 cp 2 cn 1 pp 1 pn 0 nn 0

cc 3 cp 2 cn 1 pp 1 pn 0 nn 0

ccc 3 ccp 2 ccn 2 cpp 2 ppp 1 cpn 1 cnn 1 ppn 1 pnn 0 nnn 0

8266766.doc

International Baccalaureate Physics

misinterprets the results.

© 2006 - Mike Dickinson

4/PSOW

irrelevant.

improvements.

8266766.doc