Matter deforms when stressed. Stress is defined as:
$$
\sigma=F / A
$$
where F is the force applied to an object and A is the cross-sectional area that experiences the force. Three stresses are commonly defined: tension stress, which elongate an object; compression stress, which compresses an object; and shear stress, which is the application of scissors-like forces.
The deformations produced are called strains. Strains are fractional changes in lengths:
$$
\varepsilon=\frac{\Delta \mathrm{L}}{\mathrm{~L}}
$$
where $L$ is the original length of the object.
Stress and strain are linearly related (over a given range of stresses) by Young's modulus, a material's physical property:
$$
Y=\frac{\sigma}{\varepsilon}
$$
Table 1 lists some Young's moduli for various materials, as well as their ultimate tension stresses and ultimate compression stresses (the maximum stress that a material can tolerate):
$$
\begin{array}{|l|c|c|c|}
\hline \text { Material } & \begin{array}{c}
\text { Young's } \\
\text { Modulus } \\
\left(\mathrm{N} / \mathrm{m}^2\right)
\end{array} & \begin{array}{c}
\text { Tension } \\
\text { Strength } \\
\left(\mathrm{N} / \mathrm{m}^2\right)
\end{array} & \begin{array}{c}
\text { Compression } \\
\text { Strength } \\
\left(\mathrm{N} / \mathrm{m}^2\right)
\end{array} \\
\hline \text { Aluminum } & 7 \times 10^{10} & 2 \times 10^8 & 2 \times 10^8 \\
\text { Steel } & 2 \times 10^{11} & 5 \times 10^8 & 5 \times 10^8 \\
\text { Glass } & 7 \times 10^{10} & 5 \times 10^7 & \text { not measured } \\
\text { Brass } & \text { not measured } & 2.5 \times 10^8 & 2.5 \times 10^8 \\
\text { Copper } & 9.65 \times 10^{10} & \text { not measured } & \text { not measured } \\
\text { Concrete } & \text { not measured } & 2 \times 10^6 & 2 \times 10^7 \\
\text { Bone } & 1.6 \times 10^{10} & 1.3 \times 10^8 & 1.7 \times 10^8 \\
\hline
\end{array}
$$
Table 1
A group of students decide to study the relationship between stress and strain. They do two experiments.
Experiment 1
A 5-meter-long thin steel wire is hung vertically. The wire has a cross-sectional area of $7.85 \times 10^{-7} \mathrm{~m}^2$. A $10-\mathrm{N}$ weight is hung at the lower end. The position of the lower end of the wire is read on a scale. As more load is added to the wire, the students record their data (Table 2).
$$
\begin{array}{|c|c|}
\hline \text { After Load (N) } & \text { Scale Reading (cm) } \\
\hline 0 & 4.000 \\
10 & 4.032 \\
20 & 4.064 \\
30 & 4.096 \\
40 & 4.128 \\
50 & 4.160 \\
60 & 4.192 \\
70 & 4.224 \\
\hline
\end{array}
$$
Table 2
Experiment 2
Students observe the mechanical properties of thin rods of equal size, constructed from either concrete, brass, or steel. The rods either support loads at their middle sections when oriented horizontally, or loads at their upper end when oriented vertically.
When comparing the ultimate compression and the ultimate tension strengths given in the passage the:
A. two values are always equal.
B. ultimate compression strength are always larger than the ultimate tension strength.
C. ultimate compression strength is independent of the ultimate tension strength.
D. ultimate compression force and ultimate tension force are equal only if the material is homogeneous.