1. PHYSICS 231 Lecture 23: material science and pressure
liquid
solid
gas
Remco Zegers
Walk-in hour: Monday 9:15-10:15 am
Helproom
PHY 231

2. States of matter
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3. Phase transformations
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4. solids
ordered
crystalline
amorphous
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5. The deformation of solids
Stress: Tells something about the force causing the
deformation
Strain: Measure of the degree of deformation
For small stress, strain and stress are linearly correlated.
Strain = Constant*Stress
Constant: elastic modulus
The elastic modulus depends on:
Material that is deformed
Type of deformation (a different modulus is defined for
different types of deformations)
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6. The Young’s modulus Beyond the elastic limit an object
is permanently deformed (it does
not return to its original shape if
the stress is removed).
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7. example An architect wants to design a 5m high circular pillar with
a radius of 0.5 m that holds a bronze statue that weighs
1.0E+04 kg. He chooses concrete for the material of the
pillar (Y=1.0E+10 Pa). How much does the pillar compress? 5m
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8. Ultimate strength
Ultimate strength: maximum force per unit area a material
can withstand before it breaks or fractures.
Different for
compression and tension.
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9. example A builder is stacking 1 m3 cubic concrete blocks. Each blocks
weighs 5E+03 kg. The ultimate strength of concrete for
compression is 2E+07 Pa. How many blocks can he stack
before the lowest block is crushed?
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10. The Shear Modulus x
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11. Moving earth crust
100 m
30 m
A tectonic plate in the lower crust (100 m deep) of
the earth is shifted during an earthquake by 30m.
What is the shear stress involved, if the upper layer
of the earth does not move? (S=1.5E+10 Pa)
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12. Bulk Modulus
Compressibility: 1/(Bulk modulus)
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13. example What force per unit area needs to be applied to compress
1 m3 water by 1%? (B=0.21E+10 Pa)
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14. Some typical elastic moduli
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15. Density
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16. Pressure
Pressure=F/A (N/m2=Pa)
Same Force, different pressure
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17. example A nail is driven into a piece of wood with a force of 700N.
What is the pressure on the wood if Anail=1 mm2?
A person (weighing 700 N) is lying on a bed of such
nails (his body covers 1000 nails). What is the pressure
exerted by each of the nails?
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18. Fpressure-difference= PA
Force and pressure
Air (P=1.0E+5 Pa)
P=0
Vacuum A F
What is the force needed to move the lit?
Force due to pressure difference: Fpressure=PA
If A=0.01 m2 (about 10 by 10 cm) then
a force F=(1.0E+5)*0.01=1000N is needed to pull
the lit.
Fpressure-difference= PA
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19. Magdeburg’s hemispheres
Otto von Guericke (Mayor of Magdeburg, 17th century)
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20. Pascal’s principle Pascal’s principle: a change in pressure applied
to a fluid that is enclosed is transmitted to the whole
fluid and all the walls of the container that hold the fluid.
HOLDS FOR A FLUID FULLY ENCLOSED ONLY
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21. Pascal’s principle
In other words then before: a change in pressure applied
to a fluid that is enclosed in transmitted to the whole
fluid and all the walls of the container that hold the fluid.
P=F1/A1=F2/A2
If A2>>A1 then
F2>>F1.
So, if we apply a small
force F1, we can exert
a very large Force F2.
Hydraulic press demo
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