2. Stress = Force/Area
Force is measured in units of mass*acceleration
1 N (Newton) = 1 kg * m * s-2
another common unit for force is the pound

5. Pressure is a number. It corresponds to a special kind of stress.
Stress is a tensor, but it has the same units as pressure (Pa)
1000 Pa = 1 kPa
1,000,000 Pa = 1 MPa (about 10 bars)

6. Traction is a Vector Tractions are vectors = force/area
Traction can be resolved into two components
Normal component to plane = normal stress
Tangential component = shear stress

8. The stress tensor The stress tensor is symmetric
The stress tensor has 3 principal axes
The principal axes are mutually orthogonal
principal axis = direction in which the traction vector is parallel to normal to plane => no shear stress resolved on that plane

9. = maximum compressive principal stress
= intermediate compressive principal stress
= minimum compressive principal stress

10. Normal Stress and Shear Stress
= Normal Stress resolved on plane
= shear stress resolved on plane

13. n = (1+3)/2 - [(1-3)/2] cos 2
 = [(1-3)/2] sin 2
THESE ARE ALSO THE EQUATIONS FOR A CIRCLE WITH A RADIUS OF (1-3)/2
AND A CENTER (1+3)/2 TO THE RIGHT OF WHERE THE AXES CROSS!!!!