lecture 17: giving scientific presentationsbelz/phys3719/lecture17.pdflecture 17: giving scientific...
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Lecture 17: Giving Scientific Presentations
Physics 3719Spring Semester 2011
Announcements
● Class WILL MEET Wednesday March 30th ● Choose oral presentation times:
– Mon 04/04 Alex, Oscar, Jon – Wed 04/06 Jason, Lance, Eric– Mon 04/11 Dan R, Dan B, Matt Blackmon– Wed 04/13 Stein, Charles, Wade– Mon 04/18 Matt Baird, Hans, Joseph– Wed 04/20 Jordan, Jamie
Prologue: Giving Bad Talks
Topics
● General guidelines● Miscellaneous advice● Sample presentation
General Guidelines
● Title Page (1 slide)● Intro (background and theory) (~1-2
slides)● Experimental Method (~2-3 slides)● Data and Analysis (~2-3 slides)● Discussion (~1-2 slides)● Conclusion (1 slide)
Miscellaneous Advice
● Graphics– Readable– Balance text and figures
● Be aware of time– Overall length of presentation– Remember – multiple input paths– About one minute per slide– Rehearse!
● Nervousness
Sample Presentation
Measurement of the Acceleration Due to Gravity
John BelzMarch 28, 2011
Outline
● Acceleration due to gravity● Method: The simple pendulum● Description of data analysis● Discussion of results● Concluding remarks
Background● Galileo asserted that in the
absence of air resistance all objects fall with the same constant acceleration.
● More recent experiments have confirmed this to an accuracy of a few parts in a billion:
– S. Carusotto et al., Phys. Rev. Lett. (1992).
– S. Chu et al., Nature (1999).
● What is this acceleration g?
Measuring g; Free-Fall Experiments
● Measure distance fallen over some time interval
● d = ½ gt2
● Difficulties:– Precise
measurement of distance
– Wind resistance becomes significant
Measuring g; Pendulum Experiments
● The period of oscillation is dependent on g
● Air resistance negligible
● Random error can be controlled by averaging over many oscillations.
The Simple Pendulum
Data and Analysis
● Measure with a stopwatch the time it takes for the pendulum to complete 20 oscillations. Do this ten times, and take the average to find the period T of oscillation.
● Do this for several values of the length l.● Plot l versus T2, and g is proportional to
the slope.
Experimental Data
● Result of averaging over 10 20-oscillation trials.
Linearize and Fit to Extract g
● Perform unweighted linear least-squares fit to determine slope
● Best fit gives g = 979.3 ± 3.0 cm/s2
Discussion● Good agreement with
linear l vs T2 model. 2 = 4.8/(3 df).
● Residuals indicate random error well understood
● Uncertainty in length dominates; longer pendulum would have better error in relative height.
● Averaging over more periods can improve timing uncertainty.
Conclusion
● The simple pendulum is a useful tool for measuring the acceleration due to gravity.
● Measured g = 979.3 ± 3.0 cm/sec2
● Suggested improvements to statistics and systematics have the potential to improve precision of result.