Key concepts
Nanotechnology
Matter
Strength
Engineering
 
Introduction
Have you ever seen a superhero movie where the superhero relies on a superstrong material such as Wolverine's adamantium claws, Captain America's vibranium shield or Iron Man's suit of armor? Whereas scientists and engineers in comic books work on creating fictional materials to help superheroes win the day, real-world scientists and engineers are actually already creating superstrong materials that could have a variety of uses—from improved bulletproof vests to stronger ropes to lighter bikes to better spaceships. In this activity you'll explore how simply the shape of molecules in a material can dramatically affect its strength, using nothing more than sheets of paper. Who knows, maybe this will set you on the path to designing your own super powers!
 
Background
Nanotechnology is the science of studying materials at the "nano" scale, or the scale of individual atoms and molecules. Just how small is the nanoscale? A nanometer is one billionth of a meter. A typical human hair is about 100,000 nanometers wide—so a nanometer is really small!
 
The structure of a material at the nanoscale can dramatically change how it behaves. For example, pencils contain graphite, which is made up of carbon atoms that are arranged in sheets and can easily slide around. It's easy to write with a pencil because the graphite sheets easily rub off onto paper. Carbon atoms, however, also make up some of the world's strongest materials—diamonds! In diamonds, carbon atoms are tightly packed together, making them so hard that they can cut steel.
 
Scientists are working on another superstrong version of carbon atoms called carbon nanotubes, which consist of sheets of carbon atoms rolled into tiny cylinders! Although this makes individual carbon nanotubes incredibly strong, mass-producing carbon nanotubes remains a challenge. In this activity you'll compare the strength of paper that is stacked in sheets versus rolled in tubes to simulate the difference between flaky graphite and carbon nanotubes.
 
Materials

  • Two tables, chairs or desks of equal height
  • 12 pieces of paper
  • Scotch tape or rubber bands
  • Plastic cup
  • Sturdy string or thin ribbon
  • Hole punch or sharp knife (Please use adult supervision when using the knife.)
  • Many coins, all of the same type (for example, about 250 pennies or about 100 quarters)
 
Preparation
  • Set up your two identical tables, chairs or desks so they are next to one another, with a two- to three-inch gap in between.
  • Roll six of your pieces of paper into tubes about one inch in diameter. Use Scotch tape or rubber bands to hold the paper in tube shapes.
  • Use the hole punch or knife to punch two holes on opposite sides of the cup, near the rim at the top. Cut a piece of string several feet long and tie one end of the string securely to each hole.
 
Procedure
  • Stack six sheets of paper on top of one another so they bridge the gap between your two tables. Center the sheets across the middle of the gap.
  • Hang the plastic cup from the sheets of paper so the string goes directly across the middle of the sheets (centered in the gap between the tables) and tie the two ends of the string in a knot to secure it. Do the papers sag at all under the weight of the plastic cup alone?
  • One by one, add pennies to the plastic cup until the paper falls (Note: if the string breaks before the paper, retie the knot or use a thicker string, then restart the activity). How many coins does it take to make the paper fall? What happens to the paper? Does it bend gradually or does it fold sharply in the middle?
  • Now, lay your six tubes of paper next to one another, with each one crossing the gap between the tables. Center the tubes across the middle of the gap. Make sure the tubes are pressed up against one another with no space in between.
  • Hang the plastic cup from the tubes so the string goes around all six tubes and is centered in the gap between the tables. Tie the string ends in a knot. Do the tubes sag at all under the weight of the plastic cup alone?
  • One by one, add your coins to the plastic cup until the tubes fall (Note: if the string breaks before the paper, retie the knot or use a thicker string, then restart the activity from the beginning). How many coins does it take to make the tubes fall? What happens to the tubes? Do they bend gradually? Do they fold sharply in the middle?
  • Which structure could hold more coins, the flat sheets of paper or the paper tubes? How do you think this relates to what you read about graphite and carbon nanotubes in the Background section?
  • Extra: Repeat this activity but tape the flat sheets of paper together at the edges so they cannot slide with respect to one another. You can also try taping the paper tubes together. How does this change your results? Do the structures get stronger or weaker when they are taped together?
  • Extra: Repeat the activity with different diameter paper tubes, for example half-inch- and two-inch-diameter tubes. As the tubes get bigger (or smaller) can they hold more or less weight?
  • Extra: Repeat the activity with other folded or rolled structures that you invent. For example, what happens if you fold a sheet of paper into a rectangular tube instead of a cylindrical one?  How does the strength of the tubes change as you vary their shapes? Which shape is the strongest?


Observations and results
Were the rolled sheets of paper stronger than the stacked sheets of paper?
 
You should have found that sheets of paper rolled into tubes were much stronger, and therefore could hold the weight of more coins, than sheets of paper that were simply stacked on top of one another. Just like the sheets of carbon atoms in the graphite of a pencil, stacked sheets of paper are "flaky"—they can easily slide around on top of one another, which makes them very weak and unable to hold a lot of weight. When a sheet of paper is rolled into a tube, it becomes much stronger, even though it is still the same sheet of paper. This is similar to how carbon atoms become much stronger when they form tiny cylinders in carbon nanotubes. Note that in this activity you modeled the differences between graphite sheets versus carbon nanotubes by comparing paper sheets versus paper tubes. Although physics behaves differently at the nanoscale of individual atoms compared with the "macroscale" (or the scale of everyday objects that we are used to), the general principle is still the same—you can drastically change the strength of a material simply by changing its shape.
 
More to explore
Exploring Nanotechnology: Fold, Roll & Stack Your Way to Super-Strong Materials, from Science Buddies
Nanotechnology, by Chris Woodford at Explain That Stuff!
Nanotechnology, Big Things from a Tiny World (pdf), from National Nanotechnology Coordination Office
Science Activities for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies