[LEAPSECS] props for talks?

[Poul-Henning Kamp]

In message <ED7551B7-2986-418C-9D96-224190E53537 at noao.edu>, Rob Seaman writes:


>I'm giving a colloquium in a couple of weeks and would welcome

>suggestions for neat timekeeping gizmos (borrowed or bought) to

>spark interest.


String out two naked wires across a table, preferably so they
hang 10-20 cm above the surface.

In one end you connect them to a small 3v light bulb or LED, in the
other connect them to two batteries and a switch.

Show them the light blinking.

Having a clockwork or a little motor flipping the switch on and off
every few seconds is a good stunt, otherwise have a volunteer do
the flipping on your command.

Tell them about the speed of light, tell them that the sun might
have taken a day off and we'll only know in 8 minutes time.

Next pull out your HP5370B, tell them what it does, show them how
to read the display, demonstrate it with two switches which you
press in rapid order.

Attach two scope-probes, measure the speed of light along a foot
of the wire.

Move the probes so they are two feet apart.

Etc.

The reason this is such a dramatic demonstration, is that people
hear about speed of light only in context of imense distances:
plants, spaceships or fibre-optics around the globe.

Seeing speed of light measured right in front of you, is something
few people forget easily.

Depending on the skill of the audience, you can do A-B/B-A probe-swap
and take the average, and explain that its necessary to compensate
for the difference in the probes.

Alternatively, use the SET REF to get a zero.

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