Key concepts
Physics
Materials science
Engineering
Tension
Compression

Introduction
Have you ever helped cook a pot of spaghetti? Strands of spaghetti are pretty long, so sometimes people break them in half so they more easily fit into the pot. How exactly does spaghetti break? And what does this have to do with science? It turns out engineers and materials scientists study how materials break when they are bent. Although professional engineers might be more concerned with steel beams in a bridge, you can do a fun experiment with pasta in your kitchen!

Background
What happens when you bend a piece of spaghetti (or another item)? Two things happen when you bend a material: Parts of it are put under tension, meaning they are being pulled apart. Other parts are put under compression, or being squished together. Certain materials tend to break more easily under either tension or compression, so it is important for engineers and material scientists to study how materials break. Better understanding these details allows them to build structures that won't break. Bridges are a great example—when cars drive over a bridge, their weight pushes downward, causing the bridge to bend slightly. This puts the materials in the bridge in both tension and compression. Engineers have to design the bridge to make sure it can handle these forces.

In this project you will make a "beam" from bundled-together strands of spaghetti. As you hang weights from it, the beam will start to bend—putting some of the strands in tension and some in compression. Which ones break first depends on the physical properties of pasta. Do you think pasta will break first in tension or compression? Try this project to find out!

Materials

  • Box of spaghetti
  • Two objects of equal height, such as chairs, tables or large cardboard boxes
  • Scissors (and adult's help when using them)
  • String
  • Paper clip
  • Large plastic or paper cup
  • Objects to use as weights (such as coins)
  • Rubber bands or tape
  • Recommended: safety goggles (to protect your eyes from flying fragments of broken spaghetti)

Preparation

  • Set up two equal-height chairs, tables or cardboard boxes so they are next to one another, with a gap in between them that is just a few centimeters less than the length of a piece of spaghetti.
  • Have an adult help to cut two small holes toward the top of your plastic or paper cup, just under the rim, on opposite sides from one another.
  • Tie a loop of string through the two holes in your cup to form a "handle" (turning the cup into a mini-bucket).
  • Bend a paper clip into either a "C"- or "S"-hook shape. This will allow you to hang the string handle from strands of spaghetti.

Procedure

  • Place a single piece of spaghetti across the gap between your chairs (or tables, boxes, etcetera).
  • Hang your cup from the strand of spaghetti using the paper clip hook that you made.
  • Slowly start adding weight (such as coins) to the cup. How much weight do you think the cup will hold before the strand of spaghetti breaks?
  • Continue adding weight slowly. If you are using heavy items such as coins, support the cup with your hand when you drop in a coin, then gently lower the cup until the string pulls on the spaghetti. (Do not just drop or throw coins into the cup unsupported, as this could cause the spaghetti to break more easily.)
  • Keep adding weight until the strand of spaghetti breaks. (If it bends and falls through the gap without breaking, move your chairs closer together and try again.)
  • Now, bundle together five pieces of spaghetti. Do this by wrapping their ends in either rubber bands or tape to hold them together. How much weight do you think the bundled strands of spaghetti will hold? Will it be approximately five times the amount a single strand could hold, more than that or less?
  • Place the bundled strands of spaghetti across the gap and repeat the weight test. Remember to add weight slowly. Watch and listen to what happens as you add weight. Can you see or hear any individual strands of spaghetti snap before the entire bundle breaks? Are the first strands that break at the top or bottom of the bundle?
  • Try the test again with a bundle of 10 strands of spaghetti (or more, if you have a large cup and lots of coins).
  • Observe carefully where the strands that broke are located. Are the strands that fracture first at the top or bottom of the bundle? Do you think these are in tension or compression?
  • Extra: Does how you bundle the spaghetti strands together affect how much weight they can hold? What happens if you loosely tie them with string (just enough to hold them together) versus tightly wrapping them with rubber bands or tape?
  • Extra: Continue the test with larger bundles of spaghetti. You might need to use a larger container (such as a bucket instead of a plastic cup) to break the larger bundles. You can also perform this activity using water as a weight—just be sure the setup is located outside or where spills can easily be cleaned up.

[break]
Observations and results
You should find that the spaghetti strands toward the bottom of your bundle start to break first. These are the strands that are under tension (being pulled apart). Dry pasta is brittle, meaning it tends to break very rapidly instead of bending permanently (as opposed to a ductile material such as clay, which can be stretched a lot and will change its shape before it breaks). So, when one piece of spaghetti breaks, all the other pieces might follow in quick succession. This type of brittle failure is what engineers want to avoid in structures, such as bridges. Many other factors also go into bridge design to keep them safe and standing—even under heavy weight.

More to explore
How Bridges Work, from How Stuff Works
Strength in Numbers?, from Science Buddies
Feel the Forces of a Suspension Bridge, from Scientific American
Paper Bridges, from Scientific American
Popsicle Stick Trusses: What Shape Is Strongest?, from Scientific American

 

This activity brought to you in partnership with Science Buddies

Science Buddies