Questions and Vocabulary

• How do we figure out if a structure is going to break?
• What are different structures made out of and what are their properties?
• What words do we use to describe these properties?
• How do we test these properties?

Magnitudes

Metric Prefixes Yotta- Y 1024 1 000 000 000 000 000 000 000 000 Zetta- Z 1021 1 000 000 000 000 000 000 000 Exa- E 1018 1 000 000 000 000 000 000 Peta- P 1015 1 000 000 000 000 000 Tera- T 1012 1 000 000 000 000 Giga- G 109 1 000 000 000 Mega- M 106 1 000 000 kilo- k 103 1000 hecto- h 102 100 deka- da 10 10 – – – – deci- d 10-1 0.1 centi- c 10-2 0.01 milli- m 10-3 0.001 micro- μ 10-6 0.000 001 nano- n 10-9 0.000 000 001 pico- p 10-12 0.000 000 000 001 femto- f 10-15 0.000 000 000 000 001 atto- a 10-18 0.000 000 000 000 000 001 zepto- z 10-21 0.000 000 000 000 000 000 001 yocto- y 10-24 0.000 000 000 000 000 000 000 001

In the U.S. we use the English system, but everyone else in the world (including England!) uses the metric system. You've certainly seen some of these metric prefixes before, for example: millimeters, Gigabytes, nanoseconds.

For an interesting exercise on the magnitudes of things, try and think of different measurements for which each of the above prefixes would be convenient. Here are some references:

• Eames, L., 2006. "Powers of 10," Eames Office [accessed February 16, 2006] http://powersof10.com/index.php?mod=power_detail&id_power=0..
• Lyman, P. and H.R. Varian, 2000. "How Much Information? Data Powers of Ten," School of Information Management and Systems, University of California at Berkeley [accessed February 16, 2006] http://www.sims.berkeley.edu:8000/research/projects/how-much-info/datapowers.html.

Is this stress??

When you hear the word "stress," what do you usually think of?

No, this is stress!

In terms of materials science and mechanical engineering, stress is defined as the force on a material divided by the material's cross-sectional area (A in the diagram above). We can talk about different types of stress, depending on how the force is applied. For example, if the force is tending to stretch out the material (as in the diagram on the left), we call it tensile stress. If the force is tending to squish the material (as in the diagram on the right), we call it compressive stress.