1. 9 Solids & Fluids elasticity of solids pressure and pascal’s principle
buoyancy and archimedes’ principle
Homework:
1, 3, 5, 37, 39, 56, 69, 70.

2. Solid Deformation stress = force/area = pressure
strain = fractional change in length
Solid Moduli ~ stress/strain ~ stiffness

3. Solid Deformation Length Change: stress = F/A, strain = DL/Lo,
Young’s Modulus, Y = stress/strain.
Volume Change:
stress = F/A = p, strain = -DV/Vo,
Bulk Modulus, B = -Dp/(DV/Vo)

4. Pressure, p p = force/area Unit: pascal, Pa 1 Pa = 1N/m2.
Example: 100N applied to 0.25m2. Pressure = 100/0.25 = 400N/m2.

5. Density r = mass/volume SI Unit: kg/m3 common unit: g/cm3
1,000 kg/m3 = 1 g/cm3

6. Gauge Pressure is Differential Pressure

7. Depth and Fluid Pressure
P = Po + rgd
P is the pressure at depth d.
Po is the pressure at the fluid surface
r is the fluid density
Example: increase in pressure at a depth of 1m in water = (1,000)(9.8)(1.0) Pa

8. Barometer

9. Pascal’s Principle
Example:
A2/A1 = 100
F2/F1 = 100

10. Buoyancy and Archimedes’ Principle

11. L=0.5m cube of steel in water
Vo = L3 = (0.5m)3 = m3
FB = (fl.density)(Vo)(g)
= (1,000kg/m3 )(0.125 m3 )(9.8N/kg)
= 1225N
Compare FB to W of object:
W = mg = (ob.density)(ob.volume)(g)
= (7,800)(0.125)(9.8)
= 9555N
What is its weight when under water?
W’ = W – FB = 8330N

12. 1kg object is weighed in water
W’ = 9.2N. What is its density?
FB = W – W’ = 9.8N – 9.2N = 0.6N
FB = (fl.den.)(ob.vol.)(g) = 0.6N
FB = (1000)(ob.vol.)(g) = 0.6N
(ob.vol.) = 6.12x10-5cubic meter
(ob.den.) = mass/vol. = 1kg/(6.12x10-5)
16,333 kg/m3. = g/cm3.
This is not pure gold.

14. End

15. Example: Object mass 0.150kg density 2g/cm3 is weighed in water.

17. Example: calculate speed water exits the hole in terms of the given parameters.