The Great Bungee Jump
- More of the Story. The motivation
for these first investigations.
- Background. Things to think about
as you mess around
- Questions. Challenge questions which
the messing around investigations are designed to answer
- Tools & Materials. List, description,
and suggestions for use of tools & materials need for messing around
- Investigations. Hands-on activities.
- Reporting. Suggestions for collecting,
synthesizing, and reporting the work done while messing around.
More of the Story: Initial Investigations
Our intrepid Hands on Physics students realized early in the investigation
that it would not be practical to experiment by dropping people out of
the window and decided to build a small scale model instead. After some
initial experimentation, they decided that they needed a way to accurately
measure how long it takes for the jumper to fall different distances. The
timer must be quick, accurate, and triggered automatically by the jumper.
Time is one of the most important quantities to measure in physics.
Unlike a lot of things, time can't be held in order to be measured. No
matter what you do time continues to pass. People have devised many ways
to measure time. A lot of these methods rely on either accumulating something,
like water in a water clock, or draining something like sand in an hourglass.
Water clocks and hourglasses are fine for things which happen at a leisurely
pace, but are far too slow to measure something like a falling bungee jumper.
In this section you will experiment with a time which accumulates electrons!
Electrons are small and quick, and like the water dripping into a water
clock the amount of electrons can be used to measure time. We will use
a capacitor to accumulate electrons. A capacitor is like a container
for electrons. It can be filled from a source of electrons like your low
voltage power supply, and it can be emptied by draining the electrons through
an electrical circuit. For our purposes, a voltage meter will give us an
indication of the number of electrons in the capacitor.
Tools & Materials
Activity 1: A First Model
- About 1 m of eleastic to model the bungee cord. This can be a chain
of rubber bands or a single rubber strip. (Hobby stores sell these for
- A mass. This can be a bolt, rock, a mass hanger, or a sinker used in
fishing. It should be heavy enough to stretch your eleastic to about 1.8
Activity 2: Capacitors
- Some very large capacitors. We recommend using four 1.0 F, 5.5 V electrolytic
- Two light emitting diodes (LEDs). Any LED is fine. (Radio Shack cat.
# 276-214 is a suitable red jumbo LED)
- A hand electric generator. We recommend the Genecon manual electric
generator by Nakamura Scientific Co., LTD. (available form Science Kit
& Boreal Laboratories, catalog # 64811-00. ph. 800-828-7777)
Activity 3: The Capacitor Timer
In this investigation you will need a low voltage power supply (LVPS).
Instructions for making this circuit are in the HOP unit "Introductory
Electronics: Security Systems." If you kept the LVPS from then, use
it here. If not, you have three options:
- Build the LVPS described in Introductory Electronics: Security Systems.
- Use a battery. Any small battery will work: best would be a 1.5 V "A",
"C" or "D" cell.
- Use any small lab power supply.
You will also need electronic breadboarding parts:
- A breadboard (a means of making reliable solderless connection.) If
you use the LVPS, there should be room on its breadboard.
- Wire. 22 gauge solid (not multi-strand) hook-up wire. A selection of
colors is helpful.
- Resistors: 10 Mohm, 4.7 Mohm, 1 Mohm. This circuit does not generate
much heat, so any power rating is fine, even as small as.1 W.
- Voltmeter. We suggest using a digital multimeter with high impedence
(>100 Mohm) on its low voltage range. The lowest-cost Radio Shack meter
has this property. If you are not sure, test
your capacitor and meter.
- Activity 1. A First Model Here
you simply attach a mass to a rubber band to make a scale model of the
bungee jump. You can learn a lot just by observing carefully how this acts.
- Activity 2. Capacitors To collect
accurate data on the bungee jump you need an electronic timer. You will
use a clever, low-cost time circuit based on a capacitor. Before building
the timing circuit, take some time to understand how a capacitor works.
In this activity you will investigate how capacitors store electric charge.
You will use a small, hand powered generator to make electricity which
can be held in a large capacitor. Light emitti ng diodes (LEDs) will be
used to show the direction of current.
- Activity 3. The Capacitor Timer
Here you build and test a timer capable of measuring accurately to .001
second. This is essential for studying the bungee jump scale model but
can be used in may other studies as well.
Keep a journal as scientists do, even when messing around. Record all
your questions and observations in a bound notebook. Don't erase p;
just cross out errors. Write enough so someone else could reproduce your
experiments. Diagrams can save lots of words and help make your ideas clear.
If you make measurements, record your data, with units. Tables are useful
for repeated similar measurements. To make the logic of any calcuations
clear, first record the formula you used, then show the numbers used to
evaluate the formula, and finally your answer.
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