Abstract

Objective

The objective of this experiment is to measure the bearing capacity of beams of different thicknesses made from uncooked spaghetti. Does the bearing capacity/strand increase as spaghetti is bundled together? You can also explore different fabrication methods to see which has the best strength-to-weight ratio.

Introduction

Engineers have many good reasons for testing the materials used to build structures and devices. Each of the following questions can be answered with well-designed materials tests:

• How do you choose which material to use for a particular purpose?
• How do you know that manufactured materials meet the advertised specifications?
• How do you know that the finished products have been fabricated properly?
• How long will the finished product last?
• For research and development of new materials, how do you measure progress?

Materials testing often involves deliberately breaking things, which can be fun, as we all know. In order to get good information about the strength and other properties of the material under study, it's important to carefully control the conditions of the test. Any applied force must be measured, for example. The "Stress, Strength and Strain" resource in the Bibliography is highly recommended for background information on how engineers measure and talk about material properties.

In this project, you'll be measuring the strength of beams made from strands of spaghetti. One strand of spaghetti snaps pretty easily (in fact, you'll find out just how much force it takes). What happens when you bundle spaghetti together? Does the bundle gain extra strength from numbers, or does strength simply increase proportionally with the number of strands?

You can find out making a test stand for breaking beams made from spaghetti—all you need is a gap between two tables or benches of equal height. Hang a cup or bucket from the beam, and gradually add weight until the beam breaks. Check out the Variations section for further ideas.

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• stress,
• strain,
• ductile,
• brittle,
• strength-to-weight ratio.

Questions

• What is the difference between compressive stress and tensile stress?
• When you hang a weight from the center of a beam which is supported at both ends, what stress(es) do you induce on the beam, and where?

Bibliography

• A good place to start is this Science Buddies resource written by Stanford Mechanical Engineering Professor Beth Pruitt and her students:
  Stress, Strain and Strength.
• This PBS website has great information on structural engineering, including online labs where you can learn about forces, materials, loads and structural shapes:
  WGBH, 2001. "Building Big: Bridges, Domes, Skyscrapers, Dams and Tunnels," PBS Online [accessed February 17, 2004] http://www.pbs.org/wgbh/buildingbig/index.html.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• 3 (or more) 16 oz packages of uncooked spaghetti (depends on size of beams tested),
• string or thread,
• paper clip (for hanging yogurt cup from weaker, slender beams),
• "S" hook (for hanging weight bucket from stronger, thicker beams),
• empty yogurt cup,
• sharp nail or push pin,
• plastic bucket,
• water,
• ruler,
• postal scale, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com
• test stand (two supports at equal height, with a gap between them).

Experimental Procedure

1. Do your background research and make sure that you understand the terms and concept and can answer the questions above.
2. Set up your test stand for supporting your spaghetti beams. You can use two tables, boxes, benches, etc.
3. For adding small amounts of weight (single or a few spaghetti strands), use an empty yogurt cup, some string and a paper clip.
   1. Punch three holes, 120° apart, near the top edge of the yogurt cup with a nail or a push pin.
   2. Tie string loops of equal length through each hole.
   3. Bend a paperclip into an S-shaped hook, and attach one end to the three loops. Hang the other end from your spaghetti beam for testing weight-bearing capacity.
4. For adding larger amounts of weight to thicker beams, get a sturdy S-hook from the hardware store, and hang a plastic bucket from it by the handle.
5. For both the yogurt cup and the large bucket, you can use water as the weight. The water may spill when the beam breaks. You may want to use a catch pan and have an old towel handy to clean up any spills.
6. Remember to include the weight of the empty cup or bucket in your measurements.
7. To make bundles of spaghetti strands, tie each end of the bundle together tightly with string or thread (see Variations, below, for more ideas).
8. Test at least 5 different beam sizes.
9. Test at least 3 beams of each size (5 or more is better).
10. Weigh the beam (or count # of strands), before testing.
11. Add water to the cup or bucket (in small, measured increments) until the beam breaks. Record the amount of weight needed to break each beam.
12. Watch carefully and record any observations in your lab notebook. Does breakage consistently start in a particular location on all of the beams?
13. Calculate the strength/weight ratio (or strength/# strands ratio) for each beam, and the average for each size of beam.
14. Graph your results.

Questions

• Does strength increase as a linear function of beam weight (or # of strands)?
• From your observations of beam failure, does spaghetti perform better, worse or about the same under compression vs. tension?

Variations

• How much can you increase the strength of your beams by binding with string or thread at closer intervals?
• What happens if you vary the width of the gap on your test stand?
• Instead of lashing spaghetti beams together with string or thread, explore the strength of beams held together with white glue.
  • Does the strength improve? Does the strength-to-weight ratio improve?
  • Try gluing at successively closer intervals along the length of the beam. After testing, examine the broken beams carefully. Are the glue joints stronger, weaker, or about the same strength as the spaghetti strands? Is the relationship the same for beams with different gluing intervals?
  • Use a ribbon-like pasta (like linguine) to explore the effect of geometry. Linguine I-beams might prove hard to make because of rounded edges, but you could compare beams with square cross-section vs. equilateral triangle cross-section, for example. Again, examine the broken beams to determine whether glue joints or pasta fail first.
• Use these methods to investigate the strength of materials other than spaghetti. For example, see: Stressed Out? Take a Break with this Project!.
• If you'd like to try building something more elaborate with spaghetti, see: The Leaning Tower of Pasta.
  • For more science project ideas in this area of science, see Materials Science Project Ideas.

  Credits

  Andrew Olson, Ph.D., Science Buddies

  
  Last edit date: 2011-11-18 12:52:36