About elastic properties of solids

1. -Elastic Properties of Solids
AP Physics C
Mrs. Coyle

2. • Real objects are not rigid but can deform
under the influence of an external force.
• Remember: Hooke’s Law F=-kx

3. Elastic Properties of Solids
• Length (Tensile Stress- Strain)
• Shape (Shear Stress-Strain)
• Volume (Bulk Stress-Strain)

4. Elasticity of Length- Characteristics
•
∆L
Tensile Strain=
L
Tensile
Stress=F/A

5. Elasticity in Length
•
Tensile Stress = Y x Tensile Strain
F
∆L
=Y
A
L
• Y is known as Young’s Modulus
• Units of Y are N/m2

6. Tensile Strength
Test
• Tensile Strength
Sample

8. Ex: #30
• A steel wire of diameter 1mm can
support a tension of 0.2kN. A cable to
support a tension of 20kN should have a
diameter of what order of magnitude?
• Ans: 1cm

9. Elasticity in Shape - Shear Stress= F / A

10. Example: Shear Stress
http://www.fema.gov/plan/prevent/earthquake/fema74/chapter2_2.shtm

11. http://www.fema.gov/plan/prevent/earthquake/fema74/chapter2_2.shtm

12. Shear Stress and Shear Strain
F
∆x
=S
A
h
S is the Shear
Modulus,
Unit : N/m 2

13. Ex: #33
If the shear stress in steel exceeds 4.00x108 N/m2
the steel ruptures.
a)Determine the shearing force necessary to shear a
steel bolt 1.00cm in diameter.
Ans: a) 3.14x104 N

14. Ex: #33 cont’d
b)Determine the shearing force necessary punch
a 1.00cm diameter hole in a steel plate
0.500cm thick.
Ans: b) 6.28x104 N

15. Elasticity in Volume
∆F
∆V
= −B
A
V
B is the Bulk
Modulus
Unit: N/m2

16. • Note that ΔF/A is pressure.

17. Ex:#35
When water freezes, it expands by about 9%.
What pressure increase would occur inside
your automobile engine block if the water in it
froze?
(The bulk modulus of ice is 2.00x109 N/m2 )
Ans: 1.65 x 108 N/m2

18. Explaining the inertia ball tensions.

19. • How is ΔL affected
when you have
two same springs
in series or in
parallel pulled by
the same force?