At-Home Experiment
Soap boat Derby
What’s special about detergent? You know, of
course, that liquid detergent is great for washing
dishes. But did you know that you can use liquid
detergent to stage a unique boat race?
Question
How does detergent affect things floating
on water?
StuFF You’ll Need
•paper clip
Things to do — Paper clip diver
1.Fill in the Question, Research, and Hypothesis
sections of your lab report.
•toothpick
•liquid dish-washing
detergent
•cup or glass
filled with
water
2.Float the paper clip on the surface of the water in
the cup. To do this, very gently and slowly lay the
paper clip on the water’s surface. (If you are having
trouble making it float, cut a small bit of paper
towel, lay the paper clip on top of the towel and
float that on the water’s surface. Then carefully
slide the towel out from under the paper clip.)
3.Dip the toothpick in the detergent. Place one
drop of detergent into the water. Record your
observations in the Data section of your lab report.
Things to do — Soaped-up Boat
1.Glue the boat pattern on page 5 onto the index
card. Carefully cut out the cardboard boat.
Figure 1
StuFF You’ll Need
•paper clip
•toothpick
•liquid dish-washing
detergent
2.Fill the pan with water (or you can plug up your
sink and fill it with water).
•water
•index cards
•scissors
3.Gently place your boat in the water so it floats.
•glue
•boat patterns
(see page 5)
•a large pan or bowl
4.Dip the toothpick into the liquid detergent.
5.Place one drop of detergent into the triangular
hole in the boat’s stern (back) and watch what
happens to the boat! Record your observations in
the Data section of your lab report.
6.Wash and dry the pan completely each time you
repeat this experiment. Don’t forget to replace
your soggy boat with a fresh, dry one. Use another
pattern and index card to make more boats.
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Figure 2
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Soap boat Derby
Lab Report
Question
Find the question on the previous page and write it here.
__________________________________________________
Research
Procedure
Look up water surface tension and water striders
online or in the library. Write some facts you
learned here.
Step-by-step, list what you did in this experiment.
(Hint: Check out the Things To Do section.)
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Book or Internet site(s) you used:
____________________________________________
____________________________________________
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Hypothesis
____________________________________________
Based on your research, what do you think will
happen when:
____________________________________________
A. you put a drop of detergent in the water with
the floating paper clip?
Data
____________________________________________
Record any observations you made.
____________________________________________
____________________________________________
B. you put a drop of detergent in the back
of your boat?
____________________________________________
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____________________________________________
____________________________________________
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Materials
____________________________________________
List what you used to perform this experiment.
____________________________________________
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____________________________________________
____________________________________________
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Lab Report
Soap boat Derby
Conclusion
Real world Example
Water striders can actually walk on water.
Sometimes people dump detergent in water. What
do you think happens to a water strider when
detergent is dumped in the water where it lives?
Extra Credit
Have a soap boat race with a friend. Float two
boats side-by-side in a pan. Drop two different
types of detergent into the stern holes of each
boat at exactly the same time and see which
detergent propels the winning boat.
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Answer SHEET
Soap boat Derby
Answers
Question
When the detergent is added, the paper clip sinks
and the cardboard boat zooms forward.
Real World Example
Detergent causes water striders to sink just as
the paper clip sinks. Water striders eat mosquito
larva and other insects. In what ways do you think
detergent spilled into our waterways affects our
ecosystem?
Explanation
Water molecules “stick” together. The positive
hydrogen atoms on one water molecule are
attracted to the negative oxygen atom on the next
water molecule. When they stick together at the
surface, this is called surface tension. Paper clips
don’t really float (they are more dense than water).
But by laying one carefully on the water’s surface,
you can get it to rest on the surface because the
water’s surface tension doesn’t allow the paper clip
to pass through.
a dry paper towel. If you wet the paper towel, its
ability to support the weight is weakened, and the
fruit falls through. Wetting the paper towel is similar
to breaking up the surface tension with detergent
so the paper clip falls through.
The cardboard boat floats on water. Before the
detergent was added, surface tension pulled on
the boat in all directions equally so it didn’t move.
When detergent was added to the back, the surface
tension broke apart locally as the water molecules
separated. The force pulling the boat was uneven
in the forward direction, forcing the boat to move
forward.
Detergent breaks the surface tension of water.
When the detergent was added to the cup with
the paper clip, the soap molecules squeezed in
between the water molecules, pushing them farther
apart. Because of the greater separation distance
between water molecules, their attractive force
(surface tension) is weaker. The paper clip was then
able to pass through the surface and sink to the
bottom. Picture a grapefruit being supported by
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The detergent dissolves in the water very quickly,
breaking up the surface tension everywhere in the
water within seconds. For this reason, you must
clean out the pan and put in fresh, detergent-free
water to repeat the experiment.
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Boat Pattern
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Soap boat Derby
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