lecture 17: giving scientific presentationsbelz/phys3719/lecture17.pdflecture 17: giving scientific...

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.