Re: [Phys-L] pendulum

[Todd Pedlar <pedlto01@luther.edu>]

In addition to Joe's suggestion, a very helpful thing is to just ask the
groups to measure the period of a pendulum (set them up to all have the
same length) and just let them do it.  Answer no questions about how to do
but just see what they do.

Then, compare all the results from various groups.

Invariably, some will just try to measure one oscillation (usually starting
when they drop and then trying to stop their stopwatches at the moment the
pendulum is at rest again, which is very hard to do with any precision),
etc  Some will likely try to measure N individual swings and then take the
average, and some may measure the total elapsed time for N swings and
divide by N, etc.  But don't instruct them to do that.

The scatter of results will startle many - and it gives you a good
chance to talk about what gives the most precise results, and why.

Todd

On Wed, Mar 5, 2025 at 12:21 PM Joseph Bellina via Phys-l <
phys-l@mail.phys-l.org> wrote:

> You might want to open the experiment a bit and just ask what might affect
> the period first. You  could get a list of ideas from the class….likely
> mass and amount of swing will come up. Then have different groups test what
> does affect the period by looking at one variable holding the others
> constant. Discuss why the others are held constant.  So large mass small
> mass with same length and amount of swing. They quickly find the biggest
> influence is length. Then raise the question of the pattern of that
> influence.
> Best
> Joe
> Sent from my iPhone
>
> > On Mar 5, 2025, at 10:34 AM, Shahram Mostarshed via Phys-l <
> phys-l@mail.phys-l.org> wrote:
> > The idea here is to 'linearize' the graph, since it is easier to measure
> > the slope of a straight line, unless your question is about something
> else
> > (?)
> >
> > Shahram Mostarshed
> > Physics Instructor, Stanford OHS
> >
> > > On Wed, Mar 5, 2025 at 3:02 AM Anthony Lapinski via Phys-l <
> > > phys-l@mail.phys-l.org> wrote:
> > >
> > > I might try a pendulum lab in my (high school) class when I teach about
> > > waves. Will have them time the swings, change the length, and determine
> the
> > > period. Why are most graphs online for this period squared vs length?
> > > (slope = 4pi^2/g) Since length is the independent variable, it should
> go on
> > > the y-axis - plot length vs period squared. Then the slope would be
> g/4pi^2
> > > - in m/s^2). Is there some historical tradition here, or am I missing
> > > something simple?
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-- 
Todd K. Pedlar
Professor of Physics and Physics Department Head
Luther College, Decorah, IA
pedlto01@luther.edu
(563) 387-1628
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