On a bumpy surface, little rocks or twigs can create obstacles for your
model. Unfortunately, its engine isn’t powerful enough to overcome
them.
On a smooth surface, your solar vehicle runs flawlessly. Of course, the
Sun has to be shining brightly enough.
A Drive in the Sunshine
In the next experiments, we will see how your tractor
drives in the sunlight.
Experiment 14
>
You will need: your model, bright sunlight, the
back side of a large 11 x 17-inch pad of drawing paper
or other large, solid, smooth piece of cardboard
Instructions
Lay a pad of drawing paper with its back side up, or
some other smooth, strong cardboard, in bright sun-
light. Orient the module toward the Sun. Be sure that
the cardboard is lying flat. Then let your solar tractor
drive on it.
Results
As soon as enough sunlight hits the solar module,
the engine starts to run, which turns the axles and the
wheels. The power of the sunlight is enough to run
your tractor on a smooth, even surface — your tractor
is running on solar power.
A Drive on Bumpy Ground
Up to now, you have only run your vehicle on a
smooth surface — the back side of the drawing pad.
Now we’ll see how it does on a bumpy surface.
Experiment 15
>
You will need: bright sunlight, solar model, level
but bumpy ground (e.g. a level gravel path or a lawn
that isn’t too steep)
Instructions
Let your solar tractor run in bright sunlight on a
bumpy surface. Make sure that it isn’t going uphill or
downhill. How does it perform now?
Results
Your tractor either won’t start correctly or won’t move
at all. As soon as the tires hit any little obstacle, you
have to give the model a push to get it moving again.
The engine isn’t powerful enough to overcome these
little obstacles. The solar cells simply produce too lit-
tle electricity to drive the tractor over level but bumpy
ground. The same goes for all of the model vehicles
in this experiment kit. In order to get the models to
run well on bumpy ground, you would need much
larger and more powerful solar cells. But they would
be very costly.
A Downhill Drive
You know from riding a bicycle that you have to use
much less energy to go downhill. Does the same ap-
ply to your solar vehicle? You will find out in an experi-
ment on an “inclined plane.” An inclined plane is a
firm, flat surface that can be used to make a downhill
slope.
Experiment 16
>
You will need: light, solar model, large drawing
pad or other strong cardboard
Instructions
Let your solar tractor drive down the inclined plane.
Use the back side of a drawing pad, lifting the end of
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