Strength in Numbers: Spaghetti Beams
IntroductionHave you ever helped your parents cook a pot of spaghetti? Strands of spaghetti are pretty long, so sometimes people break them in half so they fit into the pot more easily. How exactly does the 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. While professional engineers might be more concerned with steel beams in a bridge, you can still do a fun experiment with some pasta in your kitchen.
What happens when you bend a piece of spaghetti (or anything else, for that matter)? Two things happen when you bend a material. Parts of it are put under tension, meaning it is being pulled apart. Other parts are put under compression, meaning it is 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, so they can 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. This puts the materials in the bridge in both tension and compression. Engineers have to design the bridge to make sure it can handle the weight.
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 in tension or compression? Try this project to find out!
- Box of spaghetti
- Two equal-height chairs, tables, or large cardboard boxes
- Paper clip
- Large plastic or paper cup
- Something to use as weight (either water or coins work well, but if you are using water, do the project outside or be prepared to clean up spills)
- Rubber bands or tape
- Recommended: safety goggles (to protect your eyes from flying pieces of spaghetti)
- Set up two equal-height chairs, tables, benches, or cardboard boxes so they are next to each other, with a gap in between them that is a few centimeters less than the length of a piece of spaghetti.
- If you will be using water as a weight, set up the experiment outside so it will be easy to clean up.
- Cut two small holes towards the top of your plastic or paper cup, just under the rim, on opposite sides from each other. Tie a loop of string through the two holes to form a "handle" (like a little bucket).
- Bend a paper clip into either a "C" or "S" hook-shape. This will allow you to hang the string from strands of spaghetti.
- Place a single piece of spaghetti across the gap between your chairs (or tables, boxes, etc.)
- Hang your cup from the strand of spaghetti using the paper clip hook that you made.
- Slowly start adding weight (either coins or water) 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 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, as this could cause the spaghetti to break more easily.
- Keep adding weight until the strand of spaghetti breaks. If the piece of spaghetti bends and falls through the gap without breaking, move your chairs closer together and try again.
- Now, bundle together 5 pieces of spaghetti, by wrapping their ends in either rubber bands or tape to hold them together.
- Place the bundled strands of spaghetti across the gap, and repeat the experiment. 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 than that?
- 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 break before the entire bundle breaks? Are the strands that break at the top or at the bottom or 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, or a bucket you can put water in).
- Are the strands that break first at the top or bottom of the bundle? Are these strands in tension or compression?
Extra: does how you bundle the strands of spaghetti together affect how much weight they can hold? What happens if you loosely tie the strands of spaghetti together with string (just enough to hold them together) vs. tightly wrapping them together with rubber bands?
Extra: continue the test with larger bundles of spaghetti. You may need to use a larger container (like a bucket instead of a plastic
Observations and ResultsYou should find that the strands of spaghetti towards 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 like 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 like bridges. A rapid, catastrophic failure of a structure (like quickly snapping pasta) can be very dangerous.
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- Clean up any broken bits of spaghetti or spilled water from the floor.