Floating Paperclip:
Name:
Is it magic or science?
Section:
Date:
Question: How can you float a paperclip on water?
Materials:
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Water
Paperclip
Plastic cup
Pipettes
Hypothesis (if-then statement):
____________________________________
____________________________________
Test Design (procedure)
You are the scientist…develop a procedure or method that allows the paperclip
to float on water. Write your procedure in the box below.
Pushing the limits – what are the limits to the experiment?
1. How many paperclips can you get to float at one time? ____________
2. Does the shape of the paperclip affect its floating ability? What shape(s) did
you try?
___________________________________________________________________
___________________________________________________________________
Conclusion – please answer the questions in complete sentences.
1.
2.
3.
Why were we able to get a paper clip to float on water?
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
How is this properties related to the states of matter?
_____________________________________________________________
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How might surface tension be used in the natural world?
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Going Further
 Sprinkle pepper on the surface of the water. Put a drop of liquid dish soap
into the center of the cup. What happens to the pepper?
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
 Why do you think this occurred?
_____________________________________________________________
_____________________________________________________________
Teacher notes:
What’s Going On?
Surface tension is due to an attraction between the molecules in water. Water is
a polar molecule. At different ends of the molecule, it has positive and negative
charges. Water molecules tend to arrange themselves so that the positive end of
one is next to the negative end of another. It is the attraction between polar
water molecules that is responsible for what is called surface tension, which
causes the surface to act in an elastic manner. When you put liquid dish soap
into water, it disrupts the order of the water molecules and weakens the
intermolecular forces. Now the surface tension isn’t strong enough to support the
weight of a paperclip.
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Water Strider
The amazing water strider doesn't just walk on water. It skips across it with the
grace of an Olympic skater and the power of a hockey player. The insect dances up
and down to avoid being submerged by raindrops, and it can pack 15 times its
body weight without sinking.
Until now, scientists thought this seemingly Biblical ability was due to a wax
secreted on the insect's legs combined with surface tension, a property of water that
makes its boundary behave something like stretched Saran Wrap for small things.
But new research finds the water strider's legs are covered with microscopic hairs
that trap tiny air bubbles, allowing the insect to simply float.
The discovery was made by Xuefeng Gao and Lei Jiang of the Chinese Academy
of Sciences and will be detailed in the Nov. 4 issue of the journal Nature.
The effect is like water off a duck's back, Lei told LiveScience.
The discovery could lead to new water-resistant textiles, the researchers say. "But
our finding might be more helpful in designing innovative miniature aquatic
devices with drag-reducing [properties] and fast propulsion," Lei said.
Microscopic images of the insect's legs revealed that the otherwise invisible hairs,
called microsetae, are oriented in one direction and involve several layers. The
needle-shaped microsetae are each less than 3 micrometers in diameter (a human
hair is 80-100 micrometers wide).
The microsetae are scored with grooves measured in nanometers, even smaller
units that represent billionths of a meter.
Air gets trapped in the spaces among the microsetae and nanogrooves to form an
air cushion, which prevents the legs from getting wet, Lei explained. "Duck
feathers are a similar matter, but they are not as effective as the striders' legs to
achieve super water-repellence."
Scientists call the hairy legs superhydrophobic.
To rule out wax and surface tension as a viable water-walking technique, the
researchers created an artificial strider's leg and coated it with wax. It worked well
enough to support a couch-potato strider, but "but not to enable it to glide or dart
around rapidly on the surface."
Water striders flit about quickly by using their legs like oars, according to a
discovery last year by MIT mathematician John Bush and colleagues. The MIT
team used dye in lab water and high-speed video cameras to record vortices
created as the striders strode.
It is critical that water striders legs not get wet, "in order to avoid penetrating the
surface during their rowing stroke," said David Hu, who worked on the MIT
research. "If they do happen to fall through, they must generate forces ten times
their body weight to return to the surface."
In an email interview, Hu said today's result is "consistent with our 2003 study."
Create your own insect that can float on
water.
Please include:
 common name
 scientific name
 picture (drawing)
 Brief description of where it lives and what it eats.