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Mechanical
Energy
.
Summary: This activity shows mechanical energy being
converted to electrical energy.
Introduction:
Mechanical energy is simply
the energy of a moving object. This includes a moving piston,
the wheels of a moving locomotive, a hammer smashing down on
a nail, or even a rock flying through the air. This type of energy
is called "kinetic" energy. Scientists also believe
that another type of mechanical energy exists that is called
"potential" or stored energy. This type of energy is
ready for action. For example, anything that is high from the
ground has potential energy because gravity could make it fall
at anytime. In this activity you will be using kinetic mechanical
energy to light a bulb.
Materials:
- handheld generator (kit available
from Carolina Biological Cat. No. WW-95-5128)
- 2 bulb holders with bulbs and
wire connectors (Discovery Electricty kits available from Carolina
Biological Cat. No. WW-95-5060)
- voltage probe
- stop watch or clock with a second
hand
Classroom Management:
Sometimes handheld generators
and bulb kits are already available in upper level physics class.
If this is the case, try to borrow the equipment. A Genecon (which
is more expensive than the one listed in the materials list),
usually used in physics, is shown in the picture. The one suggested
in the materials list is relatively inexpensive and is often
used by younger students. Any handheld generator will work for
this activity.
Also, a set of mini "holiday
lights" can be cut easily into individual bulb sets with
the wire leads stripped so they can be easily attached in series
to the handheld generator.
Activity Steps:
1. What does a handheld generator
do?
- Connect the voltage probe to the
leads of the handheld generator.
- Turn the handle at different speeds
and observe the difference in voltage (measure of electric potential).
2. Can I make a bulb light with
a handheld generator?
- Connect the handheld generator
to the bulb holder. Slowly start to turn the handle. Caution
should be taken (depending on the type of bulb used) to not exceed
the limit of the bulb. Does the bulb light when the handle is
mo ved in the opposite direction?
- Count the number of rotations
in five seconds that it takes to just light the bulb. Compare
this to the number of rotations in 5 seconds it takes to make
the bulb glow the brightest (without blowing the bulb). How did
the number of rotations change with the brightness of the bulb?
- Repeat this process with the voltage
probe attached to the bulb holder. How did the amount of voltage
compare to the amount of mechanical work needed to light the
bulb at each brightness?
3. Make a general statement
about how mechanical energy can be converted to another form.
Extensions:
Is it harder to light more bulbs?
With your group members, design
an experiment that uses the voltage probe and two bulbs to determine
if more mechanical energy is needed to light both bulbs together
than if they were separated. Record your procedure. Repeat the
experiment three times using the voltmeter to measure the electric
potential. Average your results.
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