The Great Bungee Jump
Interfacing a Computer
Extension 3: Interfacing a Computer
The timer we used in the core experiment can be greatly improved. It is
not handy to use wires that get bent and need to be replaced each time.
Also, it would be nice to get all the data pairs in one drop instead of
having to repeat the drop so many times. This is easy for a computer that
is connected to your experiment using photogates.
This technique is sometimes called "lab interfacing", "probeware",
"microcomputer-based labs", or "MBL".
You need two special kinds of electronics, a "picket fence" and
- Photogates. The wires can be replaced by a beam of light and
a light detector. The beam of light normally illuminates the light detector.
When something interrupts the light, the light detector instantly senses
the changed light level and generates a pulse.
- Picket fence. This is a transparent tape that has dark
lines drawn on it at regular intervals. When the picket fence is pulled
through the photogate, the photogate generates a series of electrical pulses.
Each pulse is caused by the movement of one line though the photogate.
- Interface. An electronic device called a lab interface can relay
the pulses from the photogate into a computer. Some interfaces attach to
your computer's serial port; others plug into a printer port or the computer
- Timing software. The computer needs special software designed
for recording and graphing the timing data generated by your photogates
and picket fence.
With the right setup, you should be able to collect all the data you
need in one drop. Attach the picket fence to weight that represents the
bungee jumper. Set up the experiment so that the picket fence is pulled
through the picket fence as the weight drops. A little friction on the
picket fence will be needed to insure that it does not fall by itself but
only when pulled by the bungee jumper. Does this friction upset the measurment?
Many brands of interface electronics and software are available. Look
here for current information on what is available.
Decide on your experiment and what data you will collect. Before you begin
experimenting, tell your instructor what you plan.
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