Thermal Conduction (14.6)
Fouriers Law of Heat Conduction (also called Newtons Law)
W = J/s
= thermal conductivity
Property of material, table 14.5 Pg 507
A = cross-sectional area (^ heat flow)
T = TH TC
Heat flows from hot to cold
Example
Water is bein
Zeroeth Law of Thermodynamics: objects in thermal
equilibrium with a third object are in thermal equilibrium
with each other
Same temperature
Temperature Scales (12.2)
Freezing water @ Patm: 0C = 32F
Boiling water @ Patm: 100C = 212F
F = (9/5)C + 32 but
Repeating motion, takes T = period = time for one cycle (s), f =
cycles per second = Hertz (Hz)
ft = cycles in t seconds, T = time for one cycle, fT = 1 so f
= 1/T, T = 1/f
Consider x component of
Uniform Circular Motion
(UCM) with radius A
x = Acos, a =
Stefans Law
e: emissivity, how efficient a radiator is it
o
0e1
o
1 = perfect radiator and absorber (black body)
o
0 = no radiation, no absorption (mirror)
o
good vacuum thermos has mirrored walls
N/S pole snow & ice e .2 but water .8 so global
warming s
Grandfather clock
Two meanings for here: careful!
Rate of change of (varies)
2/T (constant for given L)
SHM is still the basis for timekeeping
Applications
Physical Pendulum: object with
rotational inertia I around a pivot,
C.G. d from pivot
T = 2(I/mgd)
Elasticity and Oscillations
Background
Deformation changed shape of object by forces exerted on it
Elastic deformation: object returns to original shape if
forces are removed (inelastic)
Tensile force stretching
Compressive force the opposite, in a line
N
Area and Volume Expansion
L = L + L = L0(1 + T)
Area: ab = a0b0(1 + T)2 cfw_(1+x)2 1 + 2x
A = A0(2T) or
Volume: abc = a0b0c0(1 + T)3
Find if 0.025 m3 of water expands 3.110-4 m3 from 20C
to 80C: = 3.110-4/(.02560)
= 2.07 10-4
PHY 2130
Class 36, 11/19
Sec
o
Sound: Amplitude & Intensity (12.3)
Can show that pressure amplitude p0 =
(Pm P0) and displacement amplitude s0 related by p0 = vs0
Intensity I = p02/2v (= P/A)
But perception of loudness more accurately given on
logarithmic scale in dB (decibel)
dB = 1
Bernoullis Equation (9.8)
Flow through a pipe with
changing area and height
for an ideal fluid
Bernoullis Equation (1738):
Conservation of energy
Example 1: water flows out of a large tank through a hole in the
side at the bottom. If the water level is 3
Power and Intensity
For sound, I is loudness
If wave spreads out over a cone of angles, A r 2, I 1/r2,
doubling distance cuts intensity by 4
If wave spreads out in all directions, A = 4r2 (surface area of
sphere)
Intensity can be less than this if energy